Synchronize v2.x With Changes from v1.x (#3581)

* docs(tasks): v1.x inventory, triage template, merge report; update task checklist

- Record merge-base and export v1-only commits (v2..v1)
- Document failed merge attempt: v2 file tree diverges from v1
- Mark completed checklist items 0.x, 1.x, merge report draft (5.2)

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* fix(pattern): %z with UTC pattern time shows +00:00 (port v1 09a674b7)

- z_formatter takes pattern_time_type; emit +00:00 when pattern uses UTC
- Track port in tasks/commits-ported.txt and merge-report; update checklist

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* fix(os): Windows utc_minutes_offset via mktime/_mkgmtime (port v1 b656d1ce)

- Replace GetTimeZoneInformation-based offset with v1.x mktime/_mkgmtime approach
- Add tests/test_timezone.cpp and extend pattern_formatter tests; update os.h comment

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* test(timezone): POSIX TZ with DST rules; include fcntl in tcp_client_unix (v1 ports)

- 0f7562a0: EST5EDT / IST-2IDT macros for POSIX vs Windows
- d2100d5d: fcntl.h for Unix tcp client header (v2 path)

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* feat(tcp): connect timeouts and socket IO timeouts; ci: checkout@v6 (v1 ports)

- 9ecdf5c8: connect_socket_with_timeout on Unix/Windows; tcp_sink timeout_ms
- 3c61b051: actions/checkout@v6 on all workflows
- tcp_sink: remove duplicate #pragma once

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* feat(dup_filter_sink): ctor with sink list (v1 45b67eee); add full v1 SHA triage table

- tasks/v1-triage-complete.md: 245 commits PORTED/PENDING/N/A for PRD 3A tracking
- Merge report and task checklist updated

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* feat(level): case-insensitive level_from_str; cmake: BUILD_TYPE only if top-level (v1 ports)

- 566b2d14: common.cpp + test_misc (SUPERSEDED note for d5af52d9 in triage)
- dd3ca04a: guard default CMAKE_BUILD_TYPE for add_subdirectory consumers
- Update v1-triage-complete.md counts and statuses

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* v1 parity: MSVC UTF-8, ansicolor/syslog/os, getenv, triage docs

- CMake: SPDLOG_MSVC_UTF8 + /utf-8 for real MSVC only
- ansicolor: protected target_file_; fix set_color_mode_ lock nesting
- os: drop redundant fileapi.h; spdlog::details::os::getenv via std::getenv
- tests: stopwatch waits 500ms; includes/triage/commits-ported/merge-report updates
- Reclassify superseded v1 SHAs (Sep, syslog, stopwatch ms, utf8 tests, etc.)

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* parity: ringbuffer zero capacity, utf8 assert; v1 triage sync

- ringbuffer_sink: throw if n_items==0 (#3436); test expects spdlog_ex
- utf8_to_wstrbuf: assert compares int to static_cast<int>(target.size()) (#3479)
- Triage: PORTED ad725d34 getenv, 677a2d93 stopwatch, 3f7e5028, a6215527;
  SUPERSEDED a45c9390, eeb22c13, 5673e9e5, fe4f9952, 287333ee
- tasks: 27 PORTED / 26 SUPERSEDED / 78 PENDING; merge-report + commits-ported

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* docs(tasks): note regular commits and push after parity ports

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* parity: dup_filter_sink notification level from last duplicate (#3390)

- Remove notification_level ctor arg; track skipped_msg_log_level_ on duplicate skips
- Test: skipped summary line uses same short level as duplicated messages
- Triage: 847db337 PORTED; 28/26/77 counts; merge-report + commits-ported

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* parity: UWP getenv (WINAPI_FAMILY); triage fmt/cfg/no-except

- os_windows: detect non-desktop/UWP for empty getenv (#3489)
- Triage: PORTED 8806ca65; SUPERSEDED e3f5a4fe e655dbb6; N/A ae1de0dc 548b2642
- Counts 29/28/116/72; merge-report + commits-ported

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* parity: qt_sinks sign casts (#3487); triage 9c582574 superseded

- qt_color_sink: qsizetype for UTF-8 color range lengths; index colors_ with size_t
- SUPERSEDED: 9c582574 — os_unix utc_minutes_offset already matches #3366
- Counts 30/29/70; merge-report + commits-ported

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* parity: SPDLOG_NO_TZ_OFFSET (#3483); triage #3360 superseded

- CMake: option SPDLOG_NO_TZ_OFFSET; PUBLIC compile definition when ON
- z_formatter: +??:?? when macro; else keep UTC +00:00 and local offset
- utc_minutes_offset: stub on Unix/Windows when macro
- test_pattern_formatter: %z UTC case matches placeholder when NO_TZ
- SUPERSEDED 10320184 (ScopedPadder / %D already in v2)
- Triage 31/30/68; merge-report + commits-ported

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* triage: supersede 5931a3d6 ba508057 47b7e7c7 (already on v2 tree)

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* tasks: sync 5.1 triage counts (33 superseded, 65 pending)

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* parity: MSVC/clang hygiene #3515–#3519 #3521; triage batch

- dup_filter_sink: filter_ const, const filter_duration (#3515)
- logger: should_flush uses flush_level() (#3516)
- daily_file_sink: new_filename locals (#3516)
- spdlog::should_log(level log_level) (#3519)
- example my_type value_ / ctor param (#3521)
- Triage: PORTED 1774e700 309204d5 f2a9dec0 472945ba; N/A d299603e 57505989;
  SUPERSEDED 1ef8d3ce 8cfd4a7e; fix ba508057 row

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* parity: udp_sink const udp_sink_config& (#3520); triage fc7e9c87 1685e694

- dist_sink already used std::move(sinks)
- SUPERSEDED: no common-inl.h on v2; log_with_format_ avoids fmt copy path (#3541)

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* parity: README fmt::format_to (#3259); triage 2670f47d d276069a 951c5b99

- Document ambiguous format_to fix in README user-defined type example
- SUPERSEDED: z_formatter warning, fmt11 const formatter, rotate_now + test

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* parity: lock rotate_now mutex (#3281); triage a2b42620 f355b3d5 d276069a

- rotating_file_sink::rotate_now matches #3281 (sync with sink_it_)
- SUPERSEDED: CMake 3.10..3.21 (v2 uses 3.23); daily test fmt::format; fmt11 const row

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* parity: basic_file_sink::truncate (#3280); triage fwrite/fmt/test batch

- truncate(): lock + file_helper::reopen(true)
- test basic_file_sink_truncate
- SUPERSEDED: b7e0e2c2 71925ca3 fa6605dc 885b5473 96c9a62b 1e6250e1 d7155530

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* parity: test_sink/callback iterator cast (#3315); triage Catch2 #3038

- difference_type cast for formatted.end() - eol_len (ad0f31c0)
- SUPERSEDED: c1569a3d Catch2 v3.5.0, 73e2e02b wstr_to_utf8buf bounds

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* parity: SPDLOG_WCHAR_CONSOLE WriteConsoleW path (#3092); triage b6da5944

- WIN32 option SPDLOG_WCHAR_CONSOLE; SPDLOG_UTF8_TO_WCHAR_CONSOLE in private defs
- wincolor print_range_: utf8_to_wstrbuf + WriteConsoleW when defined
- N/A: async_msg flush_callback move-assign (no v1 shape on v2)

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* triage: v1 async_logger/thread_pool + fmt 11.1 batch (15 SHAs)

- N/A: fe79bfcc 6725584e async tests 16e0d2e7 63d18842 d8e0ad46 1e7d7e07 3c23c27d
- SUPERSEDED: faa0a7a9 85bdab0c 276ee5f5 7f8060d5 96a8f625
- Counts: 58 SUPERSEDED, 129 N/A, 17 PENDING; merge-report subsection

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* Port v1 TSAN CMake (#3237); close 3A triage (MDC N/A, fmt 5A)

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* docs(triage): note 3A table complete

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* 5A: bundle fmt 12.1.0 (match v1.x), FMT_INSTALL, MSVC /wd4834, find_dependency(fmt 12)

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* docs(5.4): migration and release notes for v1 parity integration branch

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* docs: cross-link migration notes; refresh PRD/tasks/merge-report for completed 5A/3A

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* revert: remove README and PRD cross-links to migration notes

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* docs(merge-report): audit — add 9fe79692 to ports table; fix 6004e3d1 paths

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* Remove tasks

* PR comment fixes

* Fix small random issues

* Fix PR comments - un-remove the comment and allow any fmt library version

---------

Co-authored-by: Jan Moravec <jan.moravec@hidglobal.com>

.github/workflows/linux.yml

@@ -28,7 +28,7 @@ jobs:
       image: ${{ matrix.config.compiler == 'clang' && 'teeks99/clang-ubuntu' || matrix.config.compiler }}:${{ matrix.config.version }}
     name: "${{ matrix.config.compiler}} ${{ matrix.config.version }} (C++${{ matrix.config.cppstd }} ${{ matrix.config.build_type }} ${{ matrix.config.asan == 'ON' && 'ASAN' || '' }}${{ matrix.config.tsan == 'ON' && 'TSAN' || '' }})"
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Setup
         run: |
           apt-get update

.github/workflows/macos.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: macOS-latest
     name: "macOS Clang (C++17, Release)"
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Build
         run: |
           mkdir -p build && cd build

.github/workflows/windows.yml

@@ -33,7 +33,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: CMake ${{ matrix.config.GENERATOR }} CXX=${{matrix.config.CXX_STANDARD}}
         shell: pwsh
@@ -85,7 +85,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: CMake ${{ matrix.config.GENERATOR }} CXX=${{matrix.config.CXX_STANDARD}}
         shell: pwsh

CMakeLists.txt

@@ -1,45 +1,38 @@
-# Copyright(c) 2019 spdlog authors Distributed under the MIT License (http://opensource.org/licenses/MIT)
-
-cmake_minimum_required(VERSION 3.14)
-
 # ---------------------------------------------------------------------------------------
-# Start spdlog project
+# Copyright(c) 2019-present by spdlog authors.
+# Distributed under the MIT License (http://opensource.org/licenses/MIT)
 # ---------------------------------------------------------------------------------------
+cmake_minimum_required(VERSION 3.23)
 include(cmake/utils.cmake)
 include(cmake/ide.cmake)
-
 spdlog_extract_version()
-
 project(spdlog VERSION ${SPDLOG_VERSION} LANGUAGES CXX)
-
 include(GNUInstallDirs)
-
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
-
 # ---------------------------------------------------------------------------------------
 # Set default build to release
 # ---------------------------------------------------------------------------------------
 if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
-    set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose Release or Debug" FORCE)
+    # Set CMAKE_BUILD_TYPE only if this project is top-level (avoid overriding parent)
+    if ((DEFINED PROJECT_IS_TOP_LEVEL AND PROJECT_IS_TOP_LEVEL) OR
+        (NOT DEFINED PROJECT_IS_TOP_LEVEL AND CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR))
+        set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose Release or Debug" FORCE)
+    endif ()
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # Compiler config
 # ---------------------------------------------------------------------------------------
-# c++ standard >=17 is required
+# C++ standard >=17 is required
 if (NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 17)
 elseif (CMAKE_CXX_STANDARD LESS 17)
     message(FATAL_ERROR "Minimum supported CMAKE_CXX_STANDARD is 17, but it is set to ${CMAKE_CXX_STANDARD}")
 endif ()
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
-
 set(CMAKE_CXX_EXTENSIONS OFF)
-
 if (CMAKE_SYSTEM_NAME MATCHES "CYGWIN" OR CMAKE_SYSTEM_NAME MATCHES "MSYS" OR CMAKE_SYSTEM_NAME MATCHES "MINGW")
     set(CMAKE_CXX_EXTENSIONS ON)
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # Set SPDLOG_MASTER_PROJECT to ON if we are building spdlog
 # ---------------------------------------------------------------------------------------
@@ -51,95 +44,86 @@ if (NOT DEFINED SPDLOG_MASTER_PROJECT)
         set(SPDLOG_MASTER_PROJECT OFF)
     endif ()
 endif ()
-
+# ---------------------------------------------------------------------------------------
+# Options
+# ---------------------------------------------------------------------------------------
 option(SPDLOG_BUILD_ALL "Build all artifacts" OFF)
-
-# build shared option
 option(SPDLOG_BUILD_SHARED "Build shared library" OFF)
-
-# example options
 option(SPDLOG_BUILD_EXAMPLE "Build example" ${SPDLOG_MASTER_PROJECT})
-
-# testing options
 option(SPDLOG_BUILD_TESTS "Build tests" OFF)
-
-# bench options
 option(SPDLOG_BUILD_BENCH "Build benchmarks (Requires https://github.com/google/benchmark.git to be installed)" OFF)
-
+option(SPDLOG_SANITIZE_ADDRESS "Enable address sanitizer for the spdlog library and anything that links it" OFF)
-# sanitizer options
+option(SPDLOG_SANITIZE_THREAD "Enable thread sanitizer for the spdlog library and anything that links it" OFF)
-option(SPDLOG_SANITIZE_ADDRESS "Enable address sanitizer in tests" OFF)
+if (SPDLOG_SANITIZE_ADDRESS AND SPDLOG_SANITIZE_THREAD)
-
+    message(FATAL_ERROR "SPDLOG_SANITIZE_ADDRESS and SPDLOG_SANITIZE_THREAD are mutually exclusive")
-# warning options
+endif ()
 option(SPDLOG_BUILD_WARNINGS "Enable compiler warnings" OFF)
-
-# install options
 option(SPDLOG_SYSTEM_INCLUDES "Include as system headers (skip for clang-tidy)." OFF)
 option(SPDLOG_INSTALL "Generate the install target" ${SPDLOG_MASTER_PROJECT})
 option(SPDLOG_FMT_EXTERNAL "Use external fmt library instead of of fetching from gitub." OFF)
-
 if (${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
     option(SPDLOG_CLOCK_COARSE "Use CLOCK_REALTIME_COARSE instead of the regular clock," OFF)
 else ()
     set(SPDLOG_CLOCK_COARSE OFF CACHE BOOL "non supported option" FORCE)
 endif ()
-
 option(SPDLOG_PREVENT_CHILD_FD "Prevent from child processes to inherit log file descriptors" OFF)
 option(SPDLOG_NO_THREAD_ID "prevent spdlog from querying the thread id on each log call if thread id is not needed" OFF)
 option(SPDLOG_DISABLE_GLOBAL_LOGGER "Disable global logger creation" OFF)
 option(SPDLOG_NO_TLS "Disable thread local storage" OFF)
-
+option(SPDLOG_NO_TZ_OFFSET "Omit %z timezone offset (use on platforms without tm_gmtoff / full offset)" OFF)
-# clang-tidy
 option(SPDLOG_TIDY "run clang-tidy" OFF)
-
+set(SPDLOG_DEBUG_POSTFIX "-${SPDLOG_VERSION_MAJOR}.${SPDLOG_VERSION_MINOR}d" CACHE STRING
+        "Filename postfix for libraries in debug builds (empty string allowed)")
+option(SPDLOG_MSVC_UTF8 "Enable/disable MSVC /utf-8 flag (recommended for fmt)" ON)
+if (WIN32)
+    option(SPDLOG_WCHAR_CONSOLE "Decode UTF-8 and write with WriteConsoleW (Unicode console output)" OFF)
+else ()
+    set(SPDLOG_WCHAR_CONSOLE OFF CACHE BOOL "non supported option" FORCE)
+endif ()
 if (SPDLOG_TIDY)
     set(CMAKE_CXX_CLANG_TIDY "clang-tidy")
     set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
     message(STATUS "Enabled clang-tidy")
 endif ()
-
 if (SPDLOG_BUILD_SHARED)
     set(BUILD_SHARED_LIBS ON)
     set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 endif ()
-
 if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     # place dlls and libs and executables in the same directory
     set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin/$<CONFIG>)
     set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin/$<CONFIG>)
     set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin/$<CONFIG>)
     set(CMAKE_PDB_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin/$<CONFIG>)
-
     # make sure __cplusplus is defined
     add_compile_options(/Zc:__cplusplus)
     # enable parallel build for the solution
     add_compile_options(/MP)
 endif ()
-
 message(STATUS "spdlog version: ${SPDLOG_VERSION}")
 message(STATUS "spdlog build type: " ${CMAKE_BUILD_TYPE})
 message(STATUS "spdlog build shared: " ${BUILD_SHARED_LIBS})
 message(STATUS "spdlog fmt external: " ${SPDLOG_FMT_EXTERNAL})
-
 # ---------------------------------------------------------------------------------------
 # Find {fmt} library
 # ---------------------------------------------------------------------------------------
 if (SPDLOG_FMT_EXTERNAL)
-    find_package(fmt REQUIRED)
+    find_package(fmt REQUIRED CONFIG)
     message(STATUS "Using external fmt lib version: ${fmt_VERSION}")
 else ()
     include(cmake/fmtlib.cmake)
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # Threads library is required
 # ---------------------------------------------------------------------------------------
 find_package(Threads REQUIRED)
-
 # ---------------------------------------------------------------------------------------
 # Library sources
 # ---------------------------------------------------------------------------------------
 set(SPDLOG_HEADERS
         "include/spdlog/common.h"
+        "include/spdlog/file_event_handlers.h"
+        "include/spdlog/filename_t.h"
         "include/spdlog/formatter.h"
         "include/spdlog/fwd.h"
         "include/spdlog/logger.h"
@@ -182,7 +166,6 @@ set(SPDLOG_HEADERS
         "include/spdlog/sinks/tcp_sink.h"
         "include/spdlog/sinks/udp_sink.h"
         "include/spdlog/sinks/async_sink.h")
-
 set(SPDLOG_SRCS
         "src/common.cpp"
         "src/logger.cpp"
@@ -198,7 +181,6 @@ set(SPDLOG_SRCS
         "src/sinks/rotating_file_sink.cpp"
         "src/sinks/stdout_sinks.cpp"
         "src/sinks/async_sink.cpp")
-
 if (WIN32)
     list(APPEND SPDLOG_SRCS
             "src/details/os_windows.cpp"
@@ -218,7 +200,6 @@ else ()
             "include/spdlog/details/udp_client_unix.h"
             "include/spdlog/sinks/ansicolor_sink.h")
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # Check if fwrite_unlocked/_fwrite_nolock is available
 # ---------------------------------------------------------------------------------------
@@ -231,7 +212,6 @@ endif ()
 if (HAVE_FWRITE_UNLOCKED)
     set(SPDLOG_FWRITE_UNLOCKED 1)
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # spdlog library
 # ---------------------------------------------------------------------------------------
@@ -244,12 +224,12 @@ if (BUILD_SHARED_LIBS)
     target_compile_definitions(spdlog PUBLIC SPDLOG_SHARED_LIB)
     if (MSVC)
         # disable dlls related warnings on msvc
-        target_compile_options(spdlog PUBLIC $<$<AND:$<CXX_COMPILER_ID:MSVC>,$<NOT:$<COMPILE_LANGUAGE:CUDA>>>:/wd4251
+        target_compile_options(spdlog PUBLIC $<$<AND:$<CXX_COMPILER_ID:MSVC>,$<NOT:$<COMPILE_LANGUAGE:CUDA>>>:/wd4251 /wd4275>)
-                /wd4275>)
     endif ()
 else ()
     add_library(spdlog STATIC)
 endif ()
+set_target_properties(spdlog PROPERTIES CXX_VISIBILITY_PRESET hidden VISIBILITY_INLINES_HIDDEN ON)
 add_library(spdlog::spdlog ALIAS spdlog)
 target_sources(spdlog PRIVATE ${SPDLOG_SRCS})
 target_sources(
@@ -258,90 +238,88 @@ target_sources(
         TYPE HEADERS
         BASE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/include
         FILES ${SPDLOG_HEADERS})
-
 set(SPDLOG_INCLUDES_LEVEL "")
 if (SPDLOG_SYSTEM_INCLUDES)
     set(SPDLOG_INCLUDES_LEVEL "SYSTEM")
 endif ()
-
 target_include_directories(spdlog ${SPDLOG_INCLUDES_LEVEL} PUBLIC "$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>"
         "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>")
-
 target_link_libraries(spdlog PUBLIC Threads::Threads)
 target_link_libraries(spdlog PUBLIC fmt::fmt)
+if (MSVC)
+    if (SPDLOG_MSVC_UTF8)
+        # Pass /utf-8 only for real MSVC (not clang-cl); see fmtlib and #3260.
+        target_compile_options(spdlog PUBLIC $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:MSVC>>:/utf-8>)
+    endif ()
+endif ()
 spdlog_enable_warnings(spdlog)
+if (SPDLOG_SANITIZE_ADDRESS)
+    spdlog_enable_addr_sanitizer(spdlog)
+elseif (SPDLOG_SANITIZE_THREAD)
+    spdlog_enable_thread_sanitizer(spdlog)
+endif ()
 set_target_properties(spdlog PROPERTIES VERSION ${SPDLOG_VERSION} SOVERSION
         ${SPDLOG_VERSION_MAJOR}.${SPDLOG_VERSION_MINOR})
-
 set(SPDLOG_NAME spdlog-${SPDLOG_VERSION_MAJOR})
-set_target_properties(spdlog PROPERTIES DEBUG_POSTFIX "-${SPDLOG_VERSION_MAJOR}.${SPDLOG_VERSION_MINOR}d")
+set_target_properties(spdlog PROPERTIES DEBUG_POSTFIX "${SPDLOG_DEBUG_POSTFIX}")
-
 # ---------------------------------------------------------------------------------------
-# set source groups for visual studio
+# Set prefix and source group for visual studio
 # ---------------------------------------------------------------------------------------
 if (CMAKE_GENERATOR MATCHES "Visual Studio")
     source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR}/include PREFIX include FILES ${SPDLOG_HEADERS})
     source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR}/src PREFIX sources FILES ${SPDLOG_SRCS})
     source_group(sources FILES ${VERSION_RC})
 endif ()
-
 # ---------------------------------------------------------------------------------------
-# Add required libraries for Android CMake build
+# Android support
 # ---------------------------------------------------------------------------------------
 if (ANDROID)
     target_link_libraries(spdlog PUBLIC log)
 endif ()
-
 # ---------------------------------------------------------------------------------------
-# spdlog private defines according to the options
+# Private defines according to the options
 # ---------------------------------------------------------------------------------------
+set(SPDLOG_UTF8_TO_WCHAR_CONSOLE ${SPDLOG_WCHAR_CONSOLE})
 foreach (SPDLOG_OPTION
         SPDLOG_CLOCK_COARSE
         SPDLOG_PREVENT_CHILD_FD
         SPDLOG_NO_THREAD_ID
         SPDLOG_DISABLE_GLOBAL_LOGGER
         SPDLOG_NO_TLS
-        SPDLOG_FWRITE_UNLOCKED)
+        SPDLOG_FWRITE_UNLOCKED
+        SPDLOG_UTF8_TO_WCHAR_CONSOLE)
     if (${SPDLOG_OPTION})
         target_compile_definitions(spdlog PRIVATE ${SPDLOG_OPTION})
     endif ()
 endforeach ()
-
+if (SPDLOG_NO_TZ_OFFSET)
+    target_compile_definitions(spdlog PUBLIC SPDLOG_NO_TZ_OFFSET)
+endif ()
 # ---------------------------------------------------------------------------------------
 # Build binaries
 # ---------------------------------------------------------------------------------------
+# examples
 if (SPDLOG_BUILD_EXAMPLE OR SPDLOG_BUILD_ALL)
     message(STATUS "Generating example(s)")
     add_subdirectory(example)
     spdlog_enable_warnings(example)
 endif ()
-
+# tests
 if (SPDLOG_BUILD_TESTS OR SPDLOG_BUILD_ALL)
     message(STATUS "Generating tests")
     enable_testing()
     add_subdirectory(tests)
 endif ()
-
+# benchmarks
 if (SPDLOG_BUILD_BENCH OR SPDLOG_BUILD_ALL)
     message(STATUS "Generating benchmarks")
     add_subdirectory(bench)
 endif ()
-
 # ---------------------------------------------------------------------------------------
 # Install
 # ---------------------------------------------------------------------------------------
 if (SPDLOG_INSTALL)
     message(STATUS "Generating install")
-    set(project_config_in "${CMAKE_CURRENT_LIST_DIR}/cmake/spdlogConfig.cmake.in")
-    set(project_config_out "${CMAKE_CURRENT_BINARY_DIR}/spdlogConfig.cmake")
-    set(config_targets_file "spdlogConfigTargets.cmake")
-    set(version_config_file "${CMAKE_CURRENT_BINARY_DIR}/spdlogConfigVersion.cmake")
-    set(export_dest_dir "${CMAKE_INSTALL_LIBDIR}/cmake/${SPDLOG_NAME}")
-
-    # ---------------------------------------------------------------------------------------
-    # Include files
-    # ---------------------------------------------------------------------------------------
-    set(installed_include_dir "${CMAKE_INSTALL_INCLUDEDIR}/${SPDLOG_NAME}")
     install(
             TARGETS spdlog
             EXPORT spdlogTargets
@@ -351,20 +329,17 @@ if (SPDLOG_INSTALL)
             FILE_SET pub_headers
             DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${SPDLOG_NAME}")
     message(STATUS "Installing spdlog in ${CMAKE_INSTALL_LIBDIR}/${SPDLOG_NAME}")
-
+    # Install CMake spdlogConfig.cmake, spdlogConfigVersion.cmake and spdlogTargets.cmake
-    # ---------------------------------------------------------------------------------------
+    set(project_config_in "${CMAKE_CURRENT_LIST_DIR}/cmake/spdlogConfig.cmake.in")
-    # Install CMake config files
+    set(project_config_out "${CMAKE_CURRENT_BINARY_DIR}/spdlogConfig.cmake")
-    # ---------------------------------------------------------------------------------------
+    set(config_targets_file "spdlogConfigTargets.cmake")
+    set(version_config_file "${CMAKE_CURRENT_BINARY_DIR}/spdlogConfigVersion.cmake")
+    set(export_dest_dir "${CMAKE_INSTALL_LIBDIR}/cmake/${SPDLOG_NAME}")
     install(EXPORT spdlogTargets DESTINATION ${export_dest_dir} NAMESPACE spdlog:: FILE ${config_targets_file})
-
     include(CMakePackageConfigHelpers)
     configure_package_config_file("${project_config_in}" "${project_config_out}" INSTALL_DESTINATION ${export_dest_dir})
-
     write_basic_package_version_file("${version_config_file}" COMPATIBILITY SameMajorVersion)
     install(FILES "${project_config_out}" "${version_config_file}" DESTINATION "${export_dest_dir}")
-
+    # CPack
-    # ---------------------------------------------------------------------------------------
-    # Support creation of installable packages
-    # ---------------------------------------------------------------------------------------
     include(cmake/spdlogCPack.cmake)
 endif ()

README.md

@@ -41,7 +41,7 @@ see example [CMakeLists.txt](https://github.com/gabime/spdlog/blob/v2.x/example/
 ## Features
 * Very fast (see [benchmarks](#benchmarks) below).
 * Headers only or compiled
-* Feature-rich formatting, using the excellent [fmt](https://github.com/fmtlib/fmt) library.
+* Feature-rich formatting, using the excellent [fmt](https://github.com/fmtlib/fmt) library (bundled **12.1.0** by default; use `SPDLOG_FMT_EXTERNAL=ON` for a system **fmt**, **12.x** recommended).
 * Asynchronous mode (optional)
 * [Custom](https://github.com/gabime/spdlog/wiki/3.-Custom-formatting) formatting.
 * Multi/Single threaded loggers.
@@ -258,7 +258,7 @@ struct fmt::formatter<my_type> : fmt::formatter<std::string>
 {
     auto format(my_type my, format_context &ctx) const -> decltype(ctx.out())
     {
-        return format_to(ctx.out(), "[my_type i={}]", my.i);
+        return fmt::format_to(ctx.out(), "[my_type i={}]", my.i);
     }
 };
 

bench/async_bench.cpp

@@ -6,14 +6,14 @@
 //
 // bench.cpp : spdlog benchmarks
 //
+#include <algorithm>
 #include <atomic>
-#include <iostream>
 #include <fstream>
+#include <iostream>
+#include <locale>
 #include <memory>
 #include <string>
 #include <thread>
-#include <locale>
-#include <algorithm>
 
 #include "spdlog/sinks/async_sink.h"
 #include "spdlog/sinks/basic_file_sink.h"
@@ -21,8 +21,7 @@
 
 using namespace std;
 using namespace std::chrono;
-using namespace spdlog;
+using spdlog::sinks::async_sink;
-using namespace spdlog::sinks;
 
 void bench_mt(int howmany, std::shared_ptr<spdlog::logger> log, int thread_count);
 
@@ -50,8 +49,8 @@ using namespace spdlog::sinks;
 int main(int argc, char *argv[]) {
     // setlocale to show thousands separators
     std::locale::global(std::locale("en_US.UTF-8"));
-    int howmany = 1000000;
+    int howmany = 1'000'000;
-    int queue_size = std::min(howmany + 2, 8192);
+    int queue_size = async_sink::default_queue_size;
     int threads = 10;
     int iters = 3;
 
@@ -66,20 +65,23 @@ int main(int argc, char *argv[]) {
         if (argc > 2) threads = atoi(argv[2]);
         if (argc > 3) {
             queue_size = atoi(argv[3]);
-            if (queue_size > 500000) {
-                spdlog::error("Max queue size allowed: 500,000");
-                exit(1);
-            }
         }
 
         if (argc > 4) iters = atoi(argv[4]);
         // validate all argc values
-        if (howmany < 1 || threads < 1 || queue_size < 1 || iters < 1) {
+        if (howmany < 1 || threads < 1 || queue_size < 1 ||  iters < 1) {
             spdlog::error("Invalid input values");
             exit(1);
         }
 
-        auto slot_size = sizeof(details::async_log_msg);
+        constexpr int max_q_size = async_sink::max_queue_size;
+        if(queue_size > max_q_size)
+        {
+            spdlog::error("Queue size too large. Max queue size is {:L}", max_q_size);
+            exit(1);
+        }
+
+        auto slot_size = sizeof(spdlog::details::async_log_msg);
         spdlog::info("-------------------------------------------------");
         spdlog::info("Messages     : {:L}", howmany);
         spdlog::info("Threads      : {:L}", threads);
@@ -99,11 +101,11 @@ int main(int argc, char *argv[]) {
                 auto cfg = async_sink::config();
                 cfg.queue_size = queue_size;
                 cfg.sinks.push_back(std::move(file_sink));
-                auto async_sink = std::make_shared<sinks::async_sink>(cfg);
+                auto sink = std::make_shared<async_sink>(cfg);
-                auto logger = std::make_shared<spdlog::logger>("async_logger", std::move(async_sink));
+                auto logger = std::make_shared<spdlog::logger>("async_logger", std::move(sink));
                 bench_mt(howmany, std::move(logger), threads);
             }
-            //verify_file(filename, howmany); // in separate scope to ensure logger is destroyed and all logs were written
+            // verify_file(filename, howmany); // in separate scope to ensure logger is destroyed and all logs were written
         }
         spdlog::info("");
         spdlog::info("*********************************");
@@ -117,8 +119,8 @@ int main(int argc, char *argv[]) {
             cfg.queue_size = queue_size;
             auto file_sink = std::make_shared<basic_file_sink_mt>(filename, true);
             cfg.sinks.push_back(std::move(file_sink));
-            auto async_sink = std::make_shared<sinks::async_sink>(cfg);
+            auto sink = std::make_shared<async_sink>(cfg);
-            auto logger = std::make_shared<spdlog::logger>("async_logger", std::move(async_sink));
+            auto logger = std::make_shared<spdlog::logger>("async_logger", std::move(sink));
             bench_mt(howmany, std::move(logger), threads);
         }
         spdlog::shutdown();

bench/latency.cpp

@@ -124,7 +124,8 @@ int main(int argc, char *argv[]) {
         benchmark::RegisterBenchmark("basic_st", bench_logger, std::move(basic_st))->UseRealTime();
 
         // rotating st
-        auto rotating_st = spdlog::create<rotating_file_sink_st>("rotating_st", "latency_logs/rotating_st.log", file_size, rotating_files);
+        auto rotating_st =
+            spdlog::create<rotating_file_sink_st>("rotating_st", "latency_logs/rotating_st.log", file_size, rotating_files);
         benchmark::RegisterBenchmark("rotating_st", bench_logger, std::move(rotating_st))->UseRealTime();
 
         // daily st
@@ -142,7 +143,8 @@ int main(int argc, char *argv[]) {
         benchmark::RegisterBenchmark("basic_mt", bench_logger, std::move(basic_mt))->Threads(n_threads)->UseRealTime();
 
         // rotating mt
-        auto rotating_mt = spdlog::create<rotating_file_sink_mt>("rotating_mt", "latency_logs/rotating_mt.log", file_size, rotating_files);
+        auto rotating_mt =
+            spdlog::create<rotating_file_sink_mt>("rotating_mt", "latency_logs/rotating_mt.log", file_size, rotating_files);
         benchmark::RegisterBenchmark("rotating_mt", bench_logger, std::move(rotating_mt))->Threads(n_threads)->UseRealTime();
 
         // daily mt
@@ -151,7 +153,8 @@ int main(int argc, char *argv[]) {
     }
     using spdlog::sinks::async_sink;
     async_sink::config config;
-    config.queue_size = 3 * 1024 * 1024;;
+    config.queue_size = async_sink::default_queue_size;;
+
     config.sinks.push_back(std::make_shared<null_sink_st>());
     config.policy = async_sink::overflow_policy::overrun_oldest;
     auto async_logger = std::make_shared<spdlog::logger>("async_logger", std::make_shared<async_sink>(config));

cmake/fmtlib.cmake

@@ -3,13 +3,25 @@ include(FetchContent)
 FetchContent_Declare(
     fmt
     DOWNLOAD_EXTRACT_TIMESTAMP FALSE
-    URL https://github.com/fmtlib/fmt/archive/refs/tags/11.0.2.tar.gz
+    URL https://github.com/fmtlib/fmt/archive/refs/tags/12.1.0.tar.gz
-    URL_HASH SHA256=6cb1e6d37bdcb756dbbe59be438790db409cdb4868c66e888d5df9f13f7c027f)
+    URL_HASH SHA256=ea7de4299689e12b6dddd392f9896f08fb0777ac7168897a244a6d6085043fea)
 
 FetchContent_GetProperties(fmt)
 if(NOT fmt_POPULATED)
     # We do not require os features of fmt
     set(FMT_OS OFF CACHE BOOL "Disable FMT_OS" FORCE)
+    # fmt 12+ defaults FMT_INSTALL to OFF when built as a subproject; spdlog's
+    # install(EXPORT) requires fmt to participate in an export set (CMake 3.23+).
+    # Only enable fmt's install rules when spdlog installs
+    if(SPDLOG_INSTALL)
+        set(FMT_INSTALL ON CACHE BOOL "Generate the install target." FORCE)
+    else()
+        set(FMT_INSTALL OFF CACHE BOOL "Generate the install target." FORCE)
+    endif()
     FetchContent_MakeAvailable(fmt)
     set_target_properties(fmt PROPERTIES FOLDER "third-party")
+    # fmt 12.1.0: MSVC C4834 on locale_ref ctor (discarded [[nodiscard]] from isalpha); fixed on fmt master after 12.1.0.
+    if (MSVC)
+        target_compile_options(fmt PRIVATE /wd4834)
+    endif ()
 endif()

cmake/spdlogCPack.cmake

@@ -22,7 +22,7 @@ set(CPACK_DEBIAN_PACKAGE_SECTION "libs")
 set(CPACK_RPM_PACKAGE_URL ${CPACK_PROJECT_URL})
 set(CPACK_DEBIAN_PACKAGE_HOMEPAGE ${CPACK_PROJECT_URL})
 set(CPACK_RPM_PACKAGE_DESCRIPTION "Fast C++ logging library.")
-set(CPACK_DEBIAN_PACKAGE_DESCRIPTION "FastC++ logging library.")
+set(CPACK_DEBIAN_PACKAGE_DESCRIPTION "Fast C++ logging library.")
 
 if(CPACK_PACKAGE_NAME)
     set(CPACK_RPM_FILE_NAME "${CPACK_PACKAGE_NAME}-${CPACK_PACKAGE_VERSION}")

cmake/spdlogConfig.cmake.in

@@ -7,7 +7,7 @@ include(CMakeFindDependencyMacro)
 
 find_package(Threads REQUIRED)
 
-find_dependency(fmt 11 CONFIG)
+find_dependency(fmt CONFIG)
 
 set(config_targets_file @config_targets_file@)
 include("${CMAKE_CURRENT_LIST_DIR}/${config_targets_file}")

example/example.cpp

@@ -88,7 +88,7 @@ void stdout_logger_example() {
     // Create color multithreading logger.
     auto console = spdlog::create<stdout_color_sink_mt>("console");
     // or for stderr:
-    //auto console = spdlog::create<stderr_color_sink_mt>("console");
+    // auto console = spdlog::create<stderr_color_sink_mt>("console");
 }
 
 #include "spdlog/sinks/basic_file_sink.h"
@@ -203,15 +203,15 @@ void multi_sink_example() {
 
 // User defined types logging
 struct my_type {
-    int i = 0;
+    int value_ = 0;
-    explicit my_type(int i)
+    explicit my_type(int value)
-        : i(i) {}
+        : value_(value) {}
 };
 
 template <>
 struct fmt::formatter<my_type> : fmt::formatter<std::string> {
     auto format(my_type my, format_context &ctx) const -> decltype(ctx.out()) {
-        return fmt::format_to(ctx.out(), "[my_type i={}]", my.i);
+        return fmt::format_to(ctx.out(), "[my_type value={}]", my.value_);
     }
 };
 

include/spdlog/bin_to_hex.h

@@ -51,7 +51,7 @@ public:
     // do not use begin() and end() to avoid collision with fmt/ranges
     It get_begin() const { return begin_; }
     It get_end() const { return end_; }
-    size_t size_per_line() const { return size_per_line_; }
+    [[nodiscard]] size_t size_per_line() const { return size_per_line_; }
 
 private:
     It begin_, end_;
@@ -90,7 +90,7 @@ inline details::dump_info<It> to_hex(const It range_begin, const It range_end, s
 
 template <typename T>
 struct fmt::formatter<spdlog::details::dump_info<T>, char> {
-    const char delimiter = ' ';
+    char delimiter = ' ';
     bool put_newlines = true;
     bool put_delimiters = true;
     bool use_uppercase = false;
@@ -138,14 +138,14 @@ struct fmt::formatter<spdlog::details::dump_info<T>, char> {
         auto inserter = ctx.out();
         int size_per_line = static_cast<int>(the_range.size_per_line());
         auto start_of_line = the_range.get_begin();
-        for (auto i = the_range.get_begin(); i != the_range.get_end(); i++) {
+        for (auto i = the_range.get_begin(); i != the_range.get_end(); ++i) {
             auto ch = static_cast<unsigned char>(*i);
 
             if (put_newlines && (i == the_range.get_begin() || i - start_of_line >= size_per_line)) {
                 if (show_ascii && i != the_range.get_begin()) {
                     *inserter++ = delimiter;
                     *inserter++ = delimiter;
-                    for (auto j = start_of_line; j < i; j++) {
+                    for (auto j = start_of_line; j < i; ++j) {
                         auto pc = static_cast<unsigned char>(*j);
                         *inserter++ = std::isprint(pc) ? static_cast<char>(*j) : '.';
                     }
@@ -181,7 +181,7 @@ struct fmt::formatter<spdlog::details::dump_info<T>, char> {
             }
             *inserter++ = delimiter;
             *inserter++ = delimiter;
-            for (auto j = start_of_line; j != the_range.get_end(); j++) {
+            for (auto j = start_of_line; j != the_range.get_end(); ++j) {
                 auto pc = static_cast<unsigned char>(*j);
                 *inserter++ = std::isprint(pc) ? static_cast<char>(*j) : '.';
             }

include/spdlog/common.h

@@ -6,31 +6,33 @@
 #include <array>
 #include <atomic>
 #include <chrono>
+#include <cstdint>
 #include <exception>
 #include <functional>
 #include <initializer_list>
 #include <memory>
 #include <string>
 #include <string_view>
-#include <cstdint>
 
 #include "./source_loc.h"
 #include "fmt/base.h"
 #include "fmt/xchar.h"
 
-#if defined(SPDLOG_SHARED_LIB)
+// Define SPDLOG_API according to current build settings
-    #if defined(_WIN32)
+#ifndef SPDLOG_SHARED_LIB
-        #ifdef spdlog_EXPORTS
+    #define SPDLOG_API
-            #define SPDLOG_API __declspec(dllexport)
+#elif defined(_WIN32)
-        #else  // !spdlog_EXPORTS
+    #ifdef spdlog_EXPORTS
-            #define SPDLOG_API __declspec(dllimport)
+        #define SPDLOG_API __declspec(dllexport) // Export symbols when building the library
-        #endif
+    #else
-    #else  // !defined(_WIN32)
+        #define SPDLOG_API __declspec(dllimport) // Import symbols when using the library
-        #define SPDLOG_API __attribute__((visibility("default")))
     #endif
-#else  // !defined(SPDLOG_SHARED_LIB)
+#elif (defined(__GNUC__) || defined(__clang__))
+    #define SPDLOG_API __attribute__((visibility("default"))) // Export symbols for shared libraries
+#else
     #define SPDLOG_API
 #endif
+// End of SPDLOG_API definition
 
 #define SPDLOG_FMT_RUNTIME(format_string) fmt::runtime(format_string)
 #define SPDLOG_FMT_STRING(format_string) FMT_STRING(format_string)

include/spdlog/details/async_log_msg.h

@@ -4,29 +4,27 @@
 #pragma once
 
 #include <cstdint>
+
 #include "./log_msg.h"
 
 namespace spdlog {
 namespace details {
 
-
 // Extend log_msg with internal buffer to store its payload.
 // This is needed since log_msg holds string_views that points to stack data.
-
 class SPDLOG_API async_log_msg : public log_msg {
 public:
-    enum class type:std::uint8_t { log, flush, terminate };
+    enum class type : std::uint8_t { log, flush, terminate };
     async_log_msg() = default;
     explicit async_log_msg(type type);
     async_log_msg(type type, const log_msg &orig_msg);
-
     ~async_log_msg() = default;
     async_log_msg(const async_log_msg &other);
     async_log_msg(async_log_msg &&other) noexcept;
     async_log_msg &operator=(const async_log_msg &other);
     async_log_msg &operator=(async_log_msg &&other) noexcept;
+    [[nodiscard]] type message_type() const { return msg_type_; }
 
-    type message_type() const {return msg_type_;}
 private:
     type msg_type_{type::log};
     memory_buf_t buffer_;

include/spdlog/details/circular_q.h

@@ -7,6 +7,8 @@
 #include <cassert>
 #include <vector>
 
+#include <spdlog/common.h>
+
 namespace spdlog {
 namespace details {
 template <typename T>

include/spdlog/details/err_helper.h

@@ -3,21 +3,29 @@
 
 #pragma once
 
-#include <string>
+#include <chrono>
-#include <mutex>
 #include <exception>
+#include <mutex>
+#include <string>
+
 #include "spdlog/common.h"
 
-// by default, prints the error to stderr, thread safe
+// by default, prints the error to stderr, at max rate of 1/sec thread safe
 namespace spdlog {
 namespace details {
 class SPDLOG_API err_helper {
     err_handler custom_err_handler_;
+    std::chrono::steady_clock::time_point last_report_time_;
+    mutable std::mutex mutex_;
+
 public:
-    void handle_ex(const std::string& origin, const source_loc& loc, const std::exception& ex) const noexcept;
+    err_helper() = default;
-    void handle_unknown_ex(const std::string& origin, const source_loc& loc) const noexcept;
+    ~err_helper() = default;
+    err_helper(const err_helper& other);
+    err_helper(err_helper&& other) noexcept;
+    void handle_ex(const std::string& origin, const source_loc& loc, const std::exception& ex) noexcept;
+    void handle_unknown_ex(const std::string& origin, const source_loc& loc) noexcept;
     void set_err_handler(err_handler handler);
 };
-
+}  // namespace details
-
+}  // namespace spdlog
-}} // namespace spdlog::details

include/spdlog/details/fmt_helper.h

@@ -14,12 +14,12 @@ namespace details {
 namespace fmt_helper {
 
 inline void append_string_view(spdlog::string_view_t view, memory_buf_t &dest) {
-    auto *buf_ptr = view.data();
+    const auto *buf_ptr = view.data();
     dest.append(buf_ptr, buf_ptr + view.size());
 }
 
 template <typename T>
-inline void append_int(T n, memory_buf_t &dest) {
+void append_int(T n, memory_buf_t &dest) {
     fmt::format_int i(n);
     dest.append(i.data(), i.data() + i.size());
 }
@@ -36,14 +36,14 @@ constexpr unsigned int count_digits_fallback(T n) {
         if (n < 100) return count + 1;
         if (n < 1000) return count + 2;
         if (n < 10000) return count + 3;
-        n /= 10000u;
+        n /= 10000U;
         count += 4;
     }
 }
 
 template <typename T>
 inline unsigned int count_digits(T n) {
-    using count_type = typename std::conditional<(sizeof(T) > sizeof(uint32_t)), uint64_t, uint32_t>::type;
+    using count_type = std::conditional_t<(sizeof(T) > sizeof(uint32_t)), uint64_t, uint32_t>;
 
     return static_cast<unsigned int>(fmt::
 // fmt 7.0.0 renamed the internal namespace to detail.
@@ -59,8 +59,8 @@ inline unsigned int count_digits(T n) {
 inline void pad2(int n, memory_buf_t &dest) {
     if (n >= 0 && n < 100)  // 0-99
     {
-        dest.push_back(static_cast<char>('0' + n / 10));
+        dest.push_back(static_cast<char>('0' + (n / 10)));
-        dest.push_back(static_cast<char>('0' + n % 10));
+        dest.push_back(static_cast<char>('0' + (n % 10)));
     } else  // unlikely, but just in case, let fmt deal with it
     {
         fmt_lib::format_to(std::back_inserter(dest), SPDLOG_FMT_STRING("{:02}"), n);
@@ -69,18 +69,18 @@ inline void pad2(int n, memory_buf_t &dest) {
 
 template <typename T>
 inline void pad_uint(T n, unsigned int width, memory_buf_t &dest) {
-    static_assert(std::is_unsigned<T>::value, "pad_uint must get unsigned T");
+    static_assert(std::is_unsigned_v<T>, "pad_uint must get unsigned T");
-    for (auto digits = count_digits(n); digits < width; digits++) {
+    for (auto digits = count_digits(n); digits < width; ++digits) {
         dest.push_back('0');
     }
     append_int(n, dest);
 }
 
 template <typename T>
-inline void pad3(T n, memory_buf_t &dest) {
+void pad3(T n, memory_buf_t &dest) {
-    static_assert(std::is_unsigned<T>::value, "pad3 must get unsigned T");
+    static_assert(std::is_unsigned_v<T>, "pad3 must get unsigned T");
     if (n < 1000) {
-        dest.push_back(static_cast<char>(n / 100 + '0'));
+        dest.push_back(static_cast<char>((n / 100) + '0'));
         n = n % 100;
         dest.push_back(static_cast<char>((n / 10) + '0'));
         dest.push_back(static_cast<char>((n % 10) + '0'));
@@ -90,12 +90,12 @@ inline void pad3(T n, memory_buf_t &dest) {
 }
 
 template <typename T>
-inline void pad6(T n, memory_buf_t &dest) {
+void pad6(T n, memory_buf_t &dest) {
     pad_uint(n, 6, dest);
 }
 
 template <typename T>
-inline void pad9(T n, memory_buf_t &dest) {
+void pad9(T n, memory_buf_t &dest) {
     pad_uint(n, 9, dest);
 }
 
@@ -103,7 +103,7 @@ inline void pad9(T n, memory_buf_t &dest) {
 // e.g.
 // fraction<std::milliseconds>(tp) -> will return the millis part of the second
 template <typename ToDuration>
-inline ToDuration time_fraction(log_clock::time_point tp) {
+ToDuration time_fraction(log_clock::time_point tp) {
     using std::chrono::duration_cast;
     using std::chrono::seconds;
     auto duration = tp.time_since_epoch();

include/spdlog/details/mpmc_blocking_q.h

@@ -5,8 +5,8 @@
 
 // multi producer-multi consumer blocking queue.
 // enqueue(..) - will block until room found to put the new message.
-// enqueue_nowait(..) - will return immediately with false if no room left in
+// enqueue_nowait(..) - enqueue immediately; overruns oldest message if no
-// the queue.
+// room left.
 // dequeue_for(..) - will block until the queue is not empty or timeout have
 // passed.
 
@@ -47,20 +47,15 @@ public:
     }
 
     void enqueue_if_have_room(T &&item) {
-        bool pushed = false;
         {
-            std::unique_lock<std::mutex> lock(queue_mutex_);
+            std::unique_lock lock(queue_mutex_);
-            if (!q_.full()) {
+            if (q_.full()) {
-                q_.push_back(std::move(item));
+                ++discard_counter_;
-                pushed = true;
+                return;
             }
+            q_.push_back(std::move(item));
         }
-
+        push_cv_.notify_one();
-        if (pushed) {
-            push_cv_.notify_one();
-        } else {
-            ++discard_counter_;
-        }
     }
 
     // dequeue with a timeout.

include/spdlog/details/null_mutex.h

@@ -7,7 +7,6 @@
 #include <utility>
 
 // null, no cost dummy "mutex" and dummy "atomic" log level
-
 namespace spdlog {
 namespace details {
 struct null_mutex {
@@ -17,7 +16,7 @@ struct null_mutex {
 
 template <typename T>
 struct null_atomic {
-    T value;
+    T value{};
 
     null_atomic() = default;
 

include/spdlog/details/os.h

@@ -36,7 +36,7 @@ SPDLOG_API bool fopen_s(FILE **fp, const filename_t &filename, const filename_t
 // Return file size according to open FILE* object
 SPDLOG_API size_t filesize(FILE *f);
 
-// Return utc offset in minutes or throw spdlog_ex on failure
+// Return utc offset in minutes (0 on failure to compute offset)
 SPDLOG_API int utc_minutes_offset(const std::tm &tm = details::os::localtime());
 
 // Return current thread id as size_t

include/spdlog/details/tcp_client_unix.h

@@ -13,9 +13,13 @@
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <string.h>
+#include <sys/select.h>
 #include <sys/socket.h>
+#include <sys/time.h>
 #include <unistd.h>
+#include <fcntl.h>
 
+#include <cerrno>
 #include <string>
 
 #include "../common.h"
@@ -40,8 +44,67 @@ public:
 
     ~tcp_client_unix() { close(); }
 
+    static int connect_socket_with_timeout(int sockfd,
+                                             const struct sockaddr *addr,
+                                             socklen_t addrlen,
+                                             const struct timeval &tv) {
+        if (tv.tv_sec == 0 && tv.tv_usec == 0) {
+            int rv = ::connect(sockfd, addr, addrlen);
+            if (rv < 0 && errno == EISCONN) {
+                return 0;
+            }
+            return rv;
+        }
+
+        int orig_flags = ::fcntl(sockfd, F_GETFL, 0);
+        if (orig_flags < 0) {
+            return -1;
+        }
+        if (::fcntl(sockfd, F_SETFL, orig_flags | O_NONBLOCK) < 0) {
+            return -1;
+        }
+
+        int rv = ::connect(sockfd, addr, addrlen);
+        if (rv == 0 || (rv < 0 && errno == EISCONN)) {
+            ::fcntl(sockfd, F_SETFL, orig_flags);
+            return 0;
+        }
+        if (errno != EINPROGRESS) {
+            ::fcntl(sockfd, F_SETFL, orig_flags);
+            return -1;
+        }
+
+        fd_set wfds;
+        FD_ZERO(&wfds);
+        FD_SET(sockfd, &wfds);
+
+        struct timeval tv_copy = tv;
+        rv = ::select(sockfd + 1, nullptr, &wfds, nullptr, &tv_copy);
+        if (rv <= 0) {
+            ::fcntl(sockfd, F_SETFL, orig_flags);
+            if (rv == 0) {
+                errno = ETIMEDOUT;
+            }
+            return -1;
+        }
+
+        int so_error = 0;
+        socklen_t len = sizeof(so_error);
+        if (::getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &so_error, &len) < 0) {
+            ::fcntl(sockfd, F_SETFL, orig_flags);
+            return -1;
+        }
+        ::fcntl(sockfd, F_SETFL, orig_flags);
+        if (so_error != 0 && so_error != EISCONN) {
+            errno = so_error;
+            return -1;
+        }
+
+        return 0;
+    }
+
     // try to connect or throw on failure
-    void connect(const std::string &host, int port) {
+    void connect(const std::string &host, int port, int timeout_ms = 0) {
         close();
         struct addrinfo hints {};
         memset(&hints, 0, sizeof(struct addrinfo));
@@ -50,6 +113,11 @@ public:
         hints.ai_flags = AI_NUMERICSERV;  // port passed as as numeric value
         hints.ai_protocol = 0;
 
+        const int validated_timeout_ms = timeout_ms > 0 ? timeout_ms : 0;
+        struct timeval tv;
+        tv.tv_sec = validated_timeout_ms / 1000;
+        tv.tv_usec = (validated_timeout_ms % 1000) * 1000;
+
         auto port_str = std::to_string(port);
         struct addrinfo *addrinfo_result;
         auto rv = ::getaddrinfo(host.c_str(), port_str.c_str(), &hints, &addrinfo_result);
@@ -70,8 +138,11 @@ public:
                 last_errno = errno;
                 continue;
             }
-            rv = ::connect(socket_, rp->ai_addr, rp->ai_addrlen);
+#ifndef SOCK_CLOEXEC
-            if (rv == 0) {
+            ::fcntl(socket_, F_SETFD, FD_CLOEXEC);
+#endif
+            if (connect_socket_with_timeout(socket_, rp->ai_addr, rp->ai_addrlen, tv) == 0) {
+                last_errno = 0;
                 break;
             }
             last_errno = errno;
@@ -83,6 +154,11 @@ public:
             throw_spdlog_ex("::connect failed", last_errno);
         }
 
+        if (validated_timeout_ms > 0) {
+            ::setsockopt(socket_, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+            ::setsockopt(socket_, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
+        }
+
         // set TCP_NODELAY
         int enable_flag = 1;
         ::setsockopt(socket_, IPPROTO_TCP, TCP_NODELAY, reinterpret_cast<char *>(&enable_flag), sizeof(enable_flag));

include/spdlog/details/tcp_client_windows.h

@@ -58,8 +58,76 @@ public:
 
     SOCKET fd() const { return socket_; }
 
+    int connect_socket_with_timeout(SOCKET sockfd,
+                                    const struct sockaddr *addr,
+                                    int addrlen,
+                                    const timeval &tv) {
+        if (tv.tv_sec == 0 && tv.tv_usec == 0) {
+            int rv = ::connect(sockfd, addr, addrlen);
+            if (rv == SOCKET_ERROR && WSAGetLastError() == WSAEISCONN) {
+                return 0;
+            }
+            return rv;
+        }
+
+        u_long mode = 1UL;
+        if (::ioctlsocket(sockfd, FIONBIO, &mode) == SOCKET_ERROR) {
+            return SOCKET_ERROR;
+        }
+
+        int rv = ::connect(sockfd, addr, addrlen);
+        int last_error = WSAGetLastError();
+        if (rv == 0 || last_error == WSAEISCONN) {
+            mode = 0UL;
+            if (::ioctlsocket(sockfd, FIONBIO, &mode) == SOCKET_ERROR) {
+                return SOCKET_ERROR;
+            }
+            return 0;
+        }
+        if (last_error != WSAEWOULDBLOCK) {
+            mode = 0UL;
+            if (::ioctlsocket(sockfd, FIONBIO, &mode)) {
+                return SOCKET_ERROR;
+            }
+            return SOCKET_ERROR;
+        }
+
+        fd_set wfds;
+        FD_ZERO(&wfds);
+        FD_SET(sockfd, &wfds);
+
+        timeval tv_copy = tv;
+        rv = ::select(0, nullptr, &wfds, nullptr, &tv_copy);
+
+        mode = 0UL;
+        if (::ioctlsocket(sockfd, FIONBIO, &mode) == SOCKET_ERROR) {
+            return SOCKET_ERROR;
+        }
+
+        if (rv == 0) {
+            WSASetLastError(WSAETIMEDOUT);
+            return SOCKET_ERROR;
+        }
+        if (rv == SOCKET_ERROR) {
+            return SOCKET_ERROR;
+        }
+
+        int so_error = 0;
+        int len = sizeof(so_error);
+        if (::getsockopt(sockfd, SOL_SOCKET, SO_ERROR, reinterpret_cast<char *>(&so_error), &len) ==
+            SOCKET_ERROR) {
+            return SOCKET_ERROR;
+        }
+        if (so_error != 0 && so_error != WSAEISCONN) {
+            WSASetLastError(so_error);
+            return SOCKET_ERROR;
+        }
+
+        return 0;
+    }
+
     // try to connect or throw on failure
-    void connect(const std::string &host, int port) {
+    void connect(const std::string &host, int port, int timeout_ms = 0) {
         if (is_connected()) {
             close();
         }
@@ -71,13 +139,17 @@ public:
         hints.ai_flags = AI_NUMERICSERV;  // port passed as as numeric value
         hints.ai_protocol = 0;
 
+        const int validated_timeout_ms = timeout_ms > 0 ? timeout_ms : 0;
+        timeval tv;
+        tv.tv_sec = validated_timeout_ms / 1000;
+        tv.tv_usec = (validated_timeout_ms % 1000) * 1000;
+
         auto port_str = std::to_string(port);
         struct addrinfo *addrinfo_result;
         auto rv = ::getaddrinfo(host.c_str(), port_str.c_str(), &hints, &addrinfo_result);
         int last_error = 0;
         if (rv != 0) {
             last_error = ::WSAGetLastError();
-            WSACleanup();
             throw_winsock_error_("getaddrinfo failed", last_error);
         }
 
@@ -87,21 +159,25 @@ public:
             socket_ = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
             if (socket_ == INVALID_SOCKET) {
                 last_error = ::WSAGetLastError();
-                WSACleanup();
                 continue;
             }
-            if (::connect(socket_, rp->ai_addr, (int)rp->ai_addrlen) == 0) {
+            if (connect_socket_with_timeout(socket_, rp->ai_addr, (int)rp->ai_addrlen, tv) == 0) {
+                last_error = 0;
                 break;
-            } else {
-                last_error = ::WSAGetLastError();
-                close();
             }
+            last_error = WSAGetLastError();
+            ::closesocket(socket_);
+            socket_ = INVALID_SOCKET;
         }
         ::freeaddrinfo(addrinfo_result);
         if (socket_ == INVALID_SOCKET) {
-            WSACleanup();
             throw_winsock_error_("connect failed", last_error);
         }
+        if (validated_timeout_ms > 0) {
+            DWORD timeout_dword = static_cast<DWORD>(validated_timeout_ms);
+            ::setsockopt(socket_, SOL_SOCKET, SO_RCVTIMEO, (const char *)&timeout_dword, sizeof(timeout_dword));
+            ::setsockopt(socket_, SOL_SOCKET, SO_SNDTIMEO, (const char *)&timeout_dword, sizeof(timeout_dword));
+        }
 
         // set TCP_NODELAY
         int enable_flag = 1;

include/spdlog/details/udp_client_unix.h

@@ -70,9 +70,9 @@ public:
     // Send exactly n_bytes of the given data.
     // On error close the connection and throw.
     void send(const char *data, size_t n_bytes) {
-        ssize_t toslen = 0;
+        socklen_t tolen = sizeof(sockAddr_);
-        socklen_t tolen = sizeof(struct sockaddr);
+        if (::sendto(socket_, data, n_bytes, 0, reinterpret_cast<const sockaddr *>(&sockAddr_),
-        if ((toslen = ::sendto(socket_, data, n_bytes, 0, (struct sockaddr *)&sockAddr_, tolen)) == -1) {
+                     tolen) == -1) {
             throw_spdlog_ex("sendto(2) failed", errno);
         }
     }

include/spdlog/logger.h

@@ -42,7 +42,7 @@ public:
     logger(std::string name, sinks_init_list sinks)
         : logger(std::move(name), sinks.begin(), sinks.end()) {}
 
-    logger(const logger &other) ;
+    logger(const logger &other);
     logger(logger &&other) noexcept;
 
     ~logger() = default;
@@ -123,7 +123,7 @@ public:
 
     // return true if the given message should be flushed
     [[nodiscard]] bool should_flush(const details::log_msg &msg) const noexcept {
-        return (msg.log_level >= flush_level_.load(std::memory_order_relaxed)) && (msg.log_level != level::off);
+        return (msg.log_level >= flush_level()) && (msg.log_level != level::off);
     }
 
     // set the level of logging
@@ -200,7 +200,6 @@ private:
                 }
             }
         }
-
         if (should_flush(msg)) {
             flush_();
         }

include/spdlog/sinks/ansicolor_sink.h

@@ -69,15 +69,19 @@ public:
     static constexpr std::string_view red_bold = "\033[31m\033[1m";
     static constexpr std::string_view bold_on_red = "\033[1m\033[41m";
 
-private:
+protected:
-    void sink_it_(const details::log_msg &msg) override;
-    void flush_() override;
     FILE *target_file_;
+
+private:
     bool should_do_colors_;
     std::array<std::string, levels_count> colors_;
-    void print_ccode_(const string_view_t color_code);
+
-    void print_range_(const memory_buf_t &formatted, size_t start, size_t end);
+    void sink_it_(const details::log_msg &msg) override;
-    static std::string to_string_(const string_view_t sv);
+    void flush_() override;
+    void set_color_mode_(color_mode mode);
+    void print_ccode_(string_view_t color_code) const;
+    void print_range_(const memory_buf_t &formatted, size_t start, size_t end) const;
+    static std::string to_string_(string_view_t sv);
 };
 
 template <typename Mutex>

include/spdlog/sinks/async_sink.h

@@ -31,7 +31,8 @@ public:
         discard_new      // Discard the log message if the queue is full
     };
 
-    enum { default_queue_size = 8192, max_queue_size = 10 * 1024 * 1024 };
+    static constexpr size_t default_queue_size = 8192;
+    static constexpr size_t max_queue_size = 250'000;
 
     struct config {
         size_t queue_size = default_queue_size;
@@ -43,8 +44,46 @@ public:
     };
 
     explicit async_sink(config async_config);
+    async_sink(const async_sink &) = delete;
+    async_sink &operator=(const async_sink &) = delete;
+    async_sink(async_sink &&) = delete;
+    async_sink &operator=(async_sink &&) = delete;
+    ~async_sink() override;
 
-    // create an async_sink with one backend sink
+    // sink interface implementation
+    void log(const details::log_msg &msg) override;
+    void set_pattern(const std::string &pattern) override;
+    void set_formatter(std::unique_ptr<formatter> sink_formatter) override;
+    // enqueue flush request to the worker thread and return immediately(default)
+    // if you need to wait for the actual flush to finish, call wait_all() after flush() or destruct the sink
+    void flush() override;
+
+    // non sink interface methods
+
+    // wait until all logs were processed up to timeout millis and return false if timeout was reached
+    [[nodiscard]] bool wait_all(std::chrono::milliseconds timeout) const;
+
+    // wait until all logs were processed
+    void wait_all() const;
+
+    // return the number of overrun messages (effective only if policy is overrun_oldest)
+    [[nodiscard]] size_t get_overrun_counter() const;
+
+    // reset the overrun counter
+    void reset_overrun_counter() const;
+
+    // return the number of discarded messages (effective only if policy is discard_new)
+    [[nodiscard]] size_t get_discard_counter() const;
+
+    // reset the discard counter
+    void reset_discard_counter() const;
+
+    // return the current async_sink configuration
+    [[nodiscard]] const config &get_config() const;
+
+    // create an async_sink with one backend sink constructed with the given args.
+    // example:
+    // auto async_file = async_sink::with<spdlog::sinks::basic_file_sink_st>("mylog.txt");
     template <typename Sink, typename... SinkArgs>
     static std::shared_ptr<async_sink> with(SinkArgs &&...sink_args) {
         config cfg{};
@@ -52,34 +91,20 @@ public:
         return std::make_shared<async_sink>(cfg);
     }
 
-    ~async_sink() override;
-
-    // sink interface implementation
-    void log(const details::log_msg &msg) override;
-    void flush() override;
-    void set_pattern(const std::string &pattern) override;
-    void set_formatter(std::unique_ptr<formatter> sink_formatter) override;
-
-    // async sink specific methods
-    [[nodiscard]] size_t get_overrun_counter() const;
-    void reset_overrun_counter() const;
-    [[nodiscard]] size_t get_discard_counter() const;
-    void reset_discard_counter() const;
-    [[nodiscard]] const config &get_config() const;
-
 private:
     using async_log_msg = details::async_log_msg;
     using queue_t = details::mpmc_blocking_queue<async_log_msg>;
 
-    void send_message_(async_log_msg::type msg_type, const details::log_msg &msg) const;
+    void enqueue_message_(details::async_log_msg &&msg) const;
     void backend_loop_();
-    void backend_log_(const details::log_msg &msg) ;
+    void backend_log_(const details::log_msg &msg);
     void backend_flush_();
 
     config config_;
     std::unique_ptr<queue_t> q_;
     std::thread worker_thread_;
     details::err_helper err_helper_;
+    std::atomic_bool terminate_worker_ = false;
 };
 
 }  // namespace sinks

include/spdlog/sinks/base_sink.h

@@ -36,7 +36,7 @@ public:
 protected:
     // sink formatter
     std::unique_ptr<spdlog::formatter> formatter_;
-    Mutex mutex_;
+    mutable Mutex mutex_;
 
     virtual void sink_it_(const details::log_msg &msg) = 0;
     virtual void flush_() = 0;

include/spdlog/sinks/basic_file_sink.h

@@ -20,6 +20,7 @@ class basic_file_sink final : public base_sink<Mutex> {
 public:
     explicit basic_file_sink(const filename_t &filename, bool truncate = false, const file_event_handlers &event_handlers = {});
     const filename_t &filename() const;
+    void truncate();
 
 protected:
     void sink_it_(const details::log_msg &msg) override;

include/spdlog/sinks/daily_file_sink.h

@@ -55,7 +55,6 @@ struct daily_filename_format_calculator {
  * Rotating file sink based on date.
  * If truncate != false , the created file will be truncated.
  * If max_files > 0, retain only the last max_files and delete previous.
- * If max_files > 0, retain only the last max_files and delete previous.
  * Note that old log files from previous executions will not be deleted by this class,
  * rotation and deletion is only applied while the program is running.
  */
@@ -81,8 +80,8 @@ public:
         }
 
         auto now = log_clock::now();
-        auto filename = FileNameCalc::calc_filename(base_filename_, now_tm(now));
+        const auto new_filename = FileNameCalc::calc_filename(base_filename_, now_tm(now));
-        file_helper_.open(filename, truncate_);
+        file_helper_.open(new_filename, truncate_);
         rotation_tp_ = next_rotation_tp_();
 
         if (max_files_ > 0) {
@@ -100,8 +99,8 @@ protected:
         auto time = msg.time;
         bool should_rotate = time >= rotation_tp_;
         if (should_rotate) {
-            auto filename = FileNameCalc::calc_filename(base_filename_, now_tm(time));
+            const auto new_filename = FileNameCalc::calc_filename(base_filename_, now_tm(time));
-            file_helper_.open(filename, truncate_);
+            file_helper_.open(new_filename, truncate_);
             rotation_tp_ = next_rotation_tp_();
         }
         memory_buf_t formatted;
@@ -124,11 +123,11 @@ private:
         std::vector<filename_t> filenames;
         auto now = log_clock::now();
         while (filenames.size() < max_files_) {
-            auto filename = FileNameCalc::calc_filename(base_filename_, now_tm(now));
+            const auto new_filename = FileNameCalc::calc_filename(base_filename_, now_tm(now));
-            if (!path_exists(filename)) {
+            if (!path_exists(new_filename)) {
                 break;
             }
-            filenames.emplace_back(filename);
+            filenames.emplace_back(new_filename);
             now -= std::chrono::hours(24);
         }
         for (auto iter = filenames.rbegin(); iter != filenames.rend(); ++iter) {

include/spdlog/sinks/dup_filter_sink.h

@@ -5,8 +5,10 @@
 
 #include <chrono>
 #include <cstdio>
+#include <memory>
 #include <mutex>
 #include <string>
+#include <vector>
 
 #include "../details/log_msg.h"
 #include "../details/null_mutex.h"
@@ -20,8 +22,8 @@
 //     #include "spdlog/sinks/dup_filter_sink.h"
 //
 //     int main() {
-//         auto dup_filter = std::make_shared<dup_filter_sink_st>(std::chrono::seconds(5),
+//         auto dup_filter = std::make_shared<dup_filter_sink_st>(std::chrono::seconds(5));
-//         level::info); dup_filter->add_sink(std::make_shared<stdout_color_sink_mt>());
+//         dup_filter->add_sink(std::make_shared<stdout_color_sink_mt>());
 //         spdlog::logger l("logger", dup_filter);
 //         l.info("Hello");
 //         l.info("Hello");
@@ -40,21 +42,39 @@ template <typename Mutex>
 class dup_filter_sink final : public dist_sink<Mutex> {
 public:
     template <class Rep, class Period>
-    explicit dup_filter_sink(std::chrono::duration<Rep, Period> max_skip_duration, level notification_level = level::info)
+    explicit dup_filter_sink(std::chrono::duration<Rep, Period> max_skip_duration)
+        : max_skip_duration_{max_skip_duration} {}
+
+    // Optional: force the "Skipped N duplicate..." line to a fixed level.
+    template <class Rep, class Period>
+    explicit dup_filter_sink(std::chrono::duration<Rep, Period> max_skip_duration,
+                             level notification_level)
         : max_skip_duration_{max_skip_duration},
-          log_level_{notification_level} {}
+          use_fixed_notification_summary_level_{true},
+          fixed_notification_summary_level_{notification_level} {}
+
+    template <class Rep, class Period>
+    explicit dup_filter_sink(std::chrono::duration<Rep, Period> max_skip_duration,
+                             std::vector<std::shared_ptr<sink>> sinks)
+        : dist_sink<Mutex>(std::move(sinks)),
+          max_skip_duration_{max_skip_duration} {}
 
 protected:
     std::chrono::microseconds max_skip_duration_;
     log_clock::time_point last_msg_time_;
     std::string last_msg_payload_;
     size_t skip_counter_ = 0;
-    level log_level_;
+    level skipped_msg_log_level_{level::off};
+    bool use_fixed_notification_summary_level_{false};
+    level fixed_notification_summary_level_{level::info};
 
     void sink_it_(const details::log_msg &msg) override {
         bool filtered = filter_(msg);
         if (!filtered) {
             skip_counter_ += 1;
+            if (!use_fixed_notification_summary_level_) {
+                skipped_msg_log_level_ = msg.log_level;
+            }
             return;
         }
 
@@ -63,7 +83,10 @@ protected:
             char buf[64];
             auto msg_size = ::snprintf(buf, sizeof(buf), "Skipped %u duplicate messages..", static_cast<unsigned>(skip_counter_));
             if (msg_size > 0 && static_cast<size_t>(msg_size) < sizeof(buf)) {
-                details::log_msg skipped_msg{msg.source, msg.logger_name, log_level_,
+                const level summary_level = use_fixed_notification_summary_level_
+                                              ? fixed_notification_summary_level_
+                                              : skipped_msg_log_level_;
+                details::log_msg skipped_msg{msg.source, msg.logger_name, summary_level,
                                              string_view_t{buf, static_cast<size_t>(msg_size)}};
                 dist_sink<Mutex>::sink_it_(skipped_msg);
             }
@@ -77,8 +100,8 @@ protected:
     }
 
     // return whether the log msg should be displayed (true) or skipped (false)
-    bool filter_(const details::log_msg &msg) {
+    bool filter_(const details::log_msg &msg) const {
-        auto filter_duration = msg.time - last_msg_time_;
+        const auto filter_duration = msg.time - last_msg_time_;
         return (filter_duration > max_skip_duration_) || (msg.payload != last_msg_payload_);
     }
 };

include/spdlog/sinks/mongo_sink.h

@@ -16,11 +16,11 @@
 #include <mongocxx/client.hpp>
 #include <mongocxx/instance.hpp>
 #include <mongocxx/uri.hpp>
-
 #include <mutex>
-#include "../details/null_mutex.h"
+
 #include "../common.h"
 #include "../details/log_msg.h"
+#include "../details/null_mutex.h"
 #include "./base_sink.h"
 
 namespace spdlog {

include/spdlog/sinks/msvc_sink.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <mutex>
+
 #include "../details/null_mutex.h"
 #include "./base_sink.h"
 

include/spdlog/sinks/qt_sinks.h

@@ -154,8 +154,10 @@ protected:
             payload = QString::fromUtf8(str.data(), static_cast<int>(str.size()));
             // convert color ranges from byte index to character index.
             if (msg.color_range_start < msg.color_range_end) {
-                color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
+                color_range_start =
-                color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
+                    QString::fromUtf8(str.data(), static_cast<qsizetype>(msg.color_range_start)).size();
+                color_range_end =
+                    QString::fromUtf8(str.data(), static_cast<qsizetype>(msg.color_range_end)).size();
             }
         } else {
             payload = QString::fromLatin1(str.data(), static_cast<int>(str.size()));
@@ -165,7 +167,7 @@ protected:
                              qt_text_edit_,              // text edit to append to
                              std::move(payload),         // text to append
                              default_color_,             // default color
-                             colors_.at(msg.log_level),  // color to apply
+                             colors_.at(static_cast<size_t>(msg.log_level)),  // color to apply
                              color_range_start,          // color range start
                              color_range_end};           // color range end
 

include/spdlog/sinks/ringbuffer_sink.h

@@ -24,7 +24,11 @@ template <typename Mutex>
 class ringbuffer_sink final : public base_sink<Mutex> {
 public:
     explicit ringbuffer_sink(size_t n_items)
-        : q_{n_items} {}
+        : q_{n_items} {
+        if (n_items == 0) {
+            throw_spdlog_ex("ringbuffer_sink: n_items cannot be zero");
+        }
+    }
 
     void drain_raw(std::function<void(const details::async_log_msg &)> callback) {
         std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
@@ -46,7 +50,9 @@ public:
     }
 
 protected:
-    void sink_it_(const details::log_msg &msg) override { q_.push_back(details::async_log_msg{details::async_log_msg::type::log, msg}); }
+    void sink_it_(const details::log_msg &msg) override {
+        q_.push_back(details::async_log_msg{details::async_log_msg::type::log, msg});
+    }
     void flush_() override {}
 
 private:

include/spdlog/sinks/sink.h

@@ -17,8 +17,8 @@ public:
     virtual void set_formatter(std::unique_ptr<spdlog::formatter> sink_formatter) = 0;
 
     void set_level(level level) { level_.store(level, std::memory_order_relaxed); }
-    level log_level() const { return level_.load(std::memory_order_relaxed);}
+    level log_level() const { return level_.load(std::memory_order_relaxed); }
-    bool should_log(level msg_level) const {return msg_level >= level_.load(std::memory_order_relaxed);}
+    bool should_log(level msg_level) const { return msg_level >= level_.load(std::memory_order_relaxed); }
 
 protected:
     // sink log level - default is all

include/spdlog/sinks/syslog_sink.h

@@ -8,8 +8,8 @@
 #include <syslog.h>
 
 #include <array>
-#include <string>
 #include <mutex>
+#include <string>
 
 namespace spdlog {
 namespace sinks {
@@ -19,7 +19,7 @@ namespace sinks {
 template <typename Mutex>
 class syslog_sink final : public base_sink<Mutex> {
 public:
-    syslog_sink(std::string ident = "", int syslog_option = 0, int syslog_facility = LOG_USER, bool enable_formatting=false)
+    syslog_sink(std::string ident = "", int syslog_option = 0, int syslog_facility = LOG_USER, bool enable_formatting = false)
         : enable_formatting_{enable_formatting},
           syslog_levels_{{/* spdlog::level::trace      */ LOG_DEBUG,
                           /* spdlog::level::debug      */ LOG_DEBUG,

include/spdlog/sinks/tcp_sink.h

@@ -17,8 +17,6 @@
 #include <mutex>
 #include <string>
 
-#pragma once
-
 // Simple tcp client sink
 // Connects to remote address and send the formatted log.
 // Will attempt to reconnect if connection drops.
@@ -31,6 +29,7 @@ namespace sinks {
 struct tcp_sink_config {
     std::string server_host;
     int server_port;
+    int timeout_ms = 0;  // timeout for connect, send, and recv (milliseconds)
     bool lazy_connect = false;  // if true connect on first log call instead of on construction
 
     tcp_sink_config(std::string host, int port)
@@ -44,10 +43,22 @@ public:
     // connect to tcp host/port or throw if failed
     // host can be hostname or ip address
 
+    explicit tcp_sink(const std::string &host,
+                      int port,
+                      int timeout_ms = 0,
+                      bool lazy_connect = false)
+        : config_{host, port} {
+        config_.timeout_ms = timeout_ms;
+        config_.lazy_connect = lazy_connect;
+        if (!config_.lazy_connect) {
+            client_.connect(config_.server_host, config_.server_port, config_.timeout_ms);
+        }
+    }
+
     explicit tcp_sink(tcp_sink_config sink_config)
         : config_{std::move(sink_config)} {
         if (!config_.lazy_connect) {
-            this->client_.connect(config_.server_host, config_.server_port);
+            client_.connect(config_.server_host, config_.server_port, config_.timeout_ms);
         }
     }
 
@@ -58,7 +69,7 @@ protected:
         spdlog::memory_buf_t formatted;
         spdlog::sinks::base_sink<Mutex>::formatter_->format(msg, formatted);
         if (!client_.is_connected()) {
-            client_.connect(config_.server_host, config_.server_port);
+            client_.connect(config_.server_host, config_.server_port, config_.timeout_ms);
         }
         client_.send(formatted.data(), formatted.size());
     }

include/spdlog/sinks/udp_sink.h

@@ -36,7 +36,7 @@ template <typename Mutex>
 class udp_sink final : public base_sink<Mutex> {
 public:
     // host can be hostname or ip address
-    explicit udp_sink(udp_sink_config sink_config)
+    explicit udp_sink(const udp_sink_config &sink_config)
         : client_{sink_config.server_host, sink_config.server_port} {}
 
     ~udp_sink() override = default;

include/spdlog/spdlog.h

@@ -40,7 +40,7 @@ SPDLOG_API level get_level();
 SPDLOG_API void set_level(level level);
 
 // Determine whether the global logger should log messages with a certain level
-SPDLOG_API bool should_log(level level);
+SPDLOG_API bool should_log(level log_level);
 
 // Set flush level of the global logger.
 SPDLOG_API void flush_on(level level);

src/common.cpp

@@ -4,19 +4,41 @@
 #include "spdlog/common.h"
 
 #include <algorithm>
+#include <cctype>
 #include <iterator>
 
 namespace spdlog {
 
+namespace {
+bool iequals(const std::string &a, const std::string &b) {
+    return a.size() == b.size() &&
+           std::equal(a.begin(), a.end(), b.begin(), [](char ac, char bc) {
+               return std::tolower(static_cast<unsigned char>(ac)) ==
+                      std::tolower(static_cast<unsigned char>(bc));
+           });
+}
+}  // namespace
+
 spdlog::level level_from_str(const std::string &name) noexcept {
-    const auto it = std::find(std::begin(level_string_views), std::end(level_string_views), name);
+    const auto it =
-    if (it != std::end(level_string_views)) return static_cast<level>(std::distance(std::begin(level_string_views), it));
+        std::find_if(std::begin(level_string_views), std::end(level_string_views),
+                     [&name](const string_view_t &level_name) {
+                         return level_name.size() == name.size() &&
+                                std::equal(name.begin(), name.end(), level_name.begin(),
+                                           [](char a, char b) {
+                                               return std::tolower(static_cast<unsigned char>(a)) ==
+                                                      std::tolower(static_cast<unsigned char>(b));
+                                           });
+                     });
+    if (it != std::end(level_string_views)) {
+        return static_cast<level>(std::distance(std::begin(level_string_views), it));
+    }
 
     // check also for "warn" and "err" before giving up
-    if (name == "warn") {
+    if (iequals(name, "warn")) {
         return spdlog::level::warn;
     }
-    if (name == "err") {
+    if (iequals(name, "err")) {
         return level::err;
     }
     return level::off;

src/details/async_log_msg.cpp

@@ -6,7 +6,6 @@
 namespace spdlog {
 namespace details {
 
-
 async_log_msg::async_log_msg(const type type)
     : msg_type_{type} {}
 
@@ -15,21 +14,25 @@ async_log_msg::async_log_msg(const type type)
 // are compiler generated const chars* (__FILE__, __LINE__, __FUNCTION__)
 // if you pass custom strings to source location, make sure they outlive the async_log_msg
 async_log_msg::async_log_msg(const type type, const log_msg &orig_msg)
-    : log_msg{orig_msg}, msg_type_(type) {
+    : log_msg{orig_msg},
+      msg_type_(type) {
     buffer_.append(logger_name);
     buffer_.append(payload);
     update_string_views();
 }
 
 async_log_msg::async_log_msg(const async_log_msg &other)
-    : log_msg{other}, msg_type_{other.msg_type_} {
+    : log_msg{other},
+      msg_type_{other.msg_type_} {
     buffer_.append(logger_name);
     buffer_.append(payload);
     update_string_views();
 }
 
 async_log_msg::async_log_msg(async_log_msg &&other) noexcept
-    : log_msg{other}, msg_type_{other.msg_type_}, buffer_{std::move(other.buffer_)} {
+    : log_msg{other},
+      msg_type_{other.msg_type_},
+      buffer_{std::move(other.buffer_)} {
     update_string_views();
 }
 

src/details/err_helper.cpp

@@ -3,23 +3,42 @@
 
 #include "spdlog/details/err_helper.h"
 
-#include "iostream"
 #include "spdlog/details/os.h"
 
 namespace spdlog {
 namespace details {
 
+err_helper::err_helper(const err_helper &other) {
+    std::lock_guard lock(other.mutex_);
+    custom_err_handler_ = other.custom_err_handler_;
+    last_report_time_ = other.last_report_time_;
+}
+
+err_helper::err_helper(err_helper &&other) noexcept {
+    custom_err_handler_ = std::move(other.custom_err_handler_);
+    last_report_time_ = std::move(other.last_report_time_);
+}
+
 // Prints error to stderr with source location (if available). A stderr sink is not used because reaching
 // this point might indicate a problem with the logging system itself so we use fputs() directly.
-void err_helper::handle_ex(const std::string &origin, const source_loc &loc, const std::exception &ex) const noexcept {
+void err_helper::handle_ex(const std::string &origin, const source_loc &loc, const std::exception &ex) noexcept {
+    std::lock_guard lock(mutex_);
     try {
         if (custom_err_handler_) {
             custom_err_handler_(ex.what());
             return;
         }
+
+        const auto now = std::chrono::steady_clock::now();
+        if (now - last_report_time_ < std::chrono::seconds(1)) {
+            return;
+        }
+        last_report_time_ = now;
         const auto tm_time = os::localtime();
-        char date_buf[32];
+        char date_buf[64];
-        std::strftime(date_buf, sizeof(date_buf), "%Y-%m-%d %H:%M:%S", &tm_time);
+        if (std::strftime(date_buf, sizeof(date_buf), "%Y-%m-%d %H:%M:%S", &tm_time) == 0) {
+            std::snprintf(date_buf, sizeof(date_buf), "unknown time");
+        }
         std::string msg;
         if (loc.empty()) {
             msg = fmt_lib::format("[*** LOG ERROR ***] [{}] [{}] {}\n", date_buf, origin, ex.what());
@@ -29,17 +48,21 @@ void err_helper::handle_ex(const std::string &origin, const source_loc &loc, con
         }
         std::fputs(msg.c_str(), stderr);
     } catch (const std::exception &handler_ex) {
-        std::fprintf(stderr, "[*** LOG ERROR ***] [%s] caught exception during error handler: %s\n", origin.c_str(), handler_ex.what());
+        std::fprintf(stderr, "[*** LOG ERROR ***] [%s] exception during %s handler: %s\n", origin.c_str(), custom_err_handler_ ? "custom" : "default",
+                     handler_ex.what());
     } catch (...) {  // catch all exceptions
-        std::fprintf(stderr, "[*** LOG ERROR ***] [%s] caught unknown exception during error handler\n", origin.c_str());
+        std::fprintf(stderr, "[*** LOG ERROR ***] [%s] unknown exception during %s handler\n", origin.c_str(), custom_err_handler_ ? "custom" : "default");
     }
 }
 
-void err_helper::handle_unknown_ex(const std::string &origin, const source_loc &loc) const noexcept {
+void err_helper::handle_unknown_ex(const std::string &origin, const source_loc &loc) noexcept {
     handle_ex(origin, loc, std::runtime_error("unknown exception"));
 }
 
-void err_helper::set_err_handler(err_handler handler) { custom_err_handler_ = std::move(handler); }
+void err_helper::set_err_handler(err_handler handler) {
+    std::lock_guard lock(mutex_);
+    custom_err_handler_ = std::move(handler);
+}
 
 }  // namespace details
 }  // namespace spdlog

src/details/os_unix.cpp

@@ -127,10 +127,16 @@ size_t filesize(FILE *f) {
     return 0;  // will not be reached.
 }
 
-// Return utc offset in minutes or throw spdlog_ex on failure
+// Return utc offset in minutes (0 on failure to compute offset)
 int utc_minutes_offset(const std::tm &tm) {
-#if defined(sun) || defined(__sun) || defined(_AIX) || (defined(__NEWLIB__) && !defined(__TM_GMTOFF)) || \
+#if defined(SPDLOG_NO_TZ_OFFSET)
-    (!defined(_BSD_SOURCE) && !defined(_GNU_SOURCE))
+    (void)tm;
+    return 0;
+#else
+    #if defined(sun) || defined(__sun) || defined(_AIX) || \
+       (defined(__NEWLIB__) && !defined(__TM_GMTOFF)) ||  \
+       (!defined(__APPLE__) && !defined(_BSD_SOURCE) && !defined(_GNU_SOURCE) && \
+       (!defined(_POSIX_VERSION) || (_POSIX_VERSION < 202405L)))
     // 'tm_gmtoff' field is BSD extension and it's missing on SunOS/Solaris
     struct helper {
         static long int calculate_gmt_offset(const std::tm &localtm = details::os::localtime(),
@@ -163,6 +169,7 @@ int utc_minutes_offset(const std::tm &tm) {
     auto offset_seconds = tm.tm_gmtoff;
 #endif
     return static_cast<int>(offset_seconds / 60);
+#endif  // SPDLOG_NO_TZ_OFFSET
 }
 
 // Return current thread id as size_t
@@ -267,8 +274,8 @@ bool is_color_terminal() noexcept {
 bool in_terminal(FILE *file) noexcept { return ::isatty(fileno(file)) != 0; }
 
 std::string getenv(const char *field) {
-    char *buf = ::getenv(field);
+    char *buf = std::getenv(field);
-    return buf != nullptr ? buf : std::string{};
+    return buf != nullptr ? std::string(buf) : std::string{};
 }
 
 // Do fsync by FILE pointer

src/details/os_windows.cpp

@@ -6,10 +6,9 @@
 #endif
 
 // clang-format off
-#include "spdlog/details/windows_include.h" // must be included before fileapi.h etc.
+#include "spdlog/details/windows_include.h" // must be first; provides FlushFileBuffers via Windows headers
 // clang-format on
 
-#include <fileapi.h>  // for FlushFileBuffers
 #include <io.h>       // for _get_osfhandle, _isatty, _fileno
 #include <process.h>  // for _get_pid
 #include <sys/stat.h>
@@ -107,24 +106,27 @@ size_t filesize(FILE *f) {
     #pragma warning(pop)
 #endif
 
-// Return utc offset in minutes or throw spdlog_ex on failure
+// Compare the timestamp as local (mktime) vs UTC (_mkgmtime) to get the offset.
+// Matches v1.x behavior: better historical DST handling than GetTimeZoneInformation alone.
 int utc_minutes_offset(const std::tm &tm) {
-#if _WIN32_WINNT < _WIN32_WINNT_WS08
+#if defined(SPDLOG_NO_TZ_OFFSET)
-    TIME_ZONE_INFORMATION tzinfo;
+    (void)tm;
-    auto rv = ::GetTimeZoneInformation(&tzinfo);
+    return 0;
 #else
-    DYNAMIC_TIME_ZONE_INFORMATION tzinfo;
+    std::tm local_tm = tm;  // copy since mktime might adjust it (normalize dates, set tm_isdst)
-    auto rv = ::GetDynamicTimeZoneInformation(&tzinfo);
+    std::time_t local_time_t = std::mktime(&local_tm);
-#endif
+    if (local_time_t == static_cast<std::time_t>(-1)) {
-    if (rv == TIME_ZONE_ID_INVALID) throw_spdlog_ex("Failed getting timezone info. ", errno);
+        return 0;  // fallback
-
-    int offset = -tzinfo.Bias;
-    if (tm.tm_isdst) {
-        offset -= tzinfo.DaylightBias;
-    } else {
-        offset -= tzinfo.StandardBias;
     }
-    return offset;
+
+    std::time_t utc_time_t = _mkgmtime(&local_tm);
+    if (utc_time_t == static_cast<std::time_t>(-1)) {
+        return 0;  // fallback
+    }
+
+    const auto offset_seconds = utc_time_t - local_time_t;
+    return static_cast<int>(offset_seconds / 60);
+#endif
 }
 
 // Return current thread id as size_t
@@ -212,7 +214,7 @@ void utf8_to_wstrbuf(string_view_t str, wmemory_buf_t &target) {
         target.resize(result_size);
         result_size = ::MultiByteToWideChar(CP_UTF8, 0, str.data(), str_size, target.data(), result_size);
         if (result_size > 0) {
-            assert(result_size == target.size());
+            assert(result_size == static_cast<int>(target.size()));
             return;
         }
     }
@@ -220,21 +222,22 @@ void utf8_to_wstrbuf(string_view_t str, wmemory_buf_t &target) {
     throw_spdlog_ex(fmt_lib::format("MultiByteToWideChar failed. Last error: {}", ::GetLastError()));
 }
 
+#ifdef _MSC_VER
+    #pragma warning(push)
+    #pragma warning(disable : 4996)
+#endif
 std::string getenv(const char *field) {
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && defined(WINAPI_FAMILY) && defined(WINAPI_FAMILY_DESKTOP_APP) && \
-    #if defined(__cplusplus_winrt)
+    (WINAPI_FAMILY != WINAPI_FAMILY_DESKTOP_APP)
-    return std::string{};  // not supported under uwp
+    return std::string{};  // not supported on UWP / non-desktop WinRT targets (#3489)
-    #else
+#else
-    size_t len = 0;
+    char *buf = std::getenv(field);
-    char buf[128];
+    return buf != nullptr ? std::string(buf) : std::string{};
-    bool ok = ::getenv_s(&len, buf, sizeof(buf), field) == 0;
-    return ok ? buf : std::string{};
-    #endif
-#else  // revert to getenv
-    char *buf = ::getenv(field);
-    return buf != nullptr ? buf : std::string{};
 #endif
 }
+#ifdef _MSC_VER
+    #pragma warning(pop)
+#endif
 
 // Do fsync by FILE handlerpointer
 // Return true on success

src/pattern_formatter.cpp

@@ -60,6 +60,9 @@ public:
             pad_it(remaining_pad_);
         } else if (padinfo_.truncate_) {
             long new_size = static_cast<long>(dest_.size()) + remaining_pad_;
+            if (new_size < 0) {
+                new_size = 0;
+            }
             dest_.resize(static_cast<size_t>(new_size));
         }
     }
@@ -123,9 +126,8 @@ public:
 };
 
 ///////////////////////////////////////////////////////////////////////
-// Date time pattern appenders
+// Date time pattern formatters
 ///////////////////////////////////////////////////////////////////////
-
 static const char *ampm(const tm &t) { return t.tm_hour >= 12 ? "PM" : "AM"; }
 
 static int to12h(const tm &t) { return t.tm_hour > 12 ? t.tm_hour - 12 : t.tm_hour; }
@@ -248,7 +250,7 @@ public:
         : flag_formatter(padinfo) {}
 
     void format(const details::log_msg &, const std::tm &tm_time, memory_buf_t &dest) override {
-        constexpr size_t field_size = 10;
+        constexpr size_t field_size = 8;
         ScopedPadder p(field_size, padinfo_, dest);
 
         fmt_helper::pad2(tm_time.tm_mon + 1, dest);
@@ -494,10 +496,10 @@ public:
 template <typename ScopedPadder>
 class z_formatter final : public flag_formatter {
 public:
-    explicit z_formatter(padding_info padinfo)
+    explicit z_formatter(padding_info padinfo, pattern_time_type time_type)
-        : flag_formatter(padinfo) {}
+        : flag_formatter(padinfo),
+          time_type_(time_type) {}
 
-    z_formatter() = default;
     ~z_formatter() override = default;
     z_formatter(const z_formatter &) = delete;
     z_formatter &operator=(const z_formatter &) = delete;
@@ -507,6 +509,17 @@ public:
     void format(const details::log_msg &msg, const std::tm &tm_time, memory_buf_t &dest) override {
         constexpr size_t field_size = 6;
         ScopedPadder p(field_size, padinfo_, dest);
+
+#ifdef SPDLOG_NO_TZ_OFFSET
+        const char *const placeholder = "+??:??";
+        dest.append(placeholder, placeholder + 6);
+#else
+        if (time_type_ == pattern_time_type::utc) {
+            const char *zeroes = "+00:00";
+            dest.append(zeroes, zeroes + 6);
+            return;
+        }
+
         auto total_minutes = get_cached_offset(msg, tm_time);
         if (total_minutes < 0) {
             total_minutes = -total_minutes;
@@ -517,9 +530,11 @@ public:
         fmt_helper::pad2(total_minutes / 60, dest);  // hours
         dest.push_back(':');
         fmt_helper::pad2(total_minutes % 60, dest);  // minutes
+#endif
     }
 
 private:
+    pattern_time_type time_type_;
     log_clock::time_point last_update_{std::chrono::seconds(0)};
     int offset_minutes_{0};
 
@@ -742,12 +757,25 @@ private:
 
 // Full info formatter
 // pattern: [%Y-%m-%d %H:%M:%S.%e] [%n] [%l] [%s:%#] %v
-class full_formatter final : public flag_formatter {
+class default_format_formatter final : public flag_formatter {
 public:
-    explicit full_formatter(padding_info padinfo)
+    // clang-format off
+    // aligned level names
+    static constexpr std::string_view trace_str =    "[trace] ";
+    static constexpr std::string_view debug_str =    "[debug] ";
+    static constexpr std::string_view info_str  =    "[info ] ";
+    static constexpr std::string_view warn_str  =    "[warn ] ";
+    static constexpr std::string_view error_str =    "[error] ";
+    static constexpr std::string_view critical_str = "[crit ] ";
+    static constexpr std::string_view off_str =      "[off  ] ";
+    // clang-format on
+    static constexpr std::array<std::string_view, levels_count> padded_levels{
+        {trace_str, debug_str, info_str, warn_str, error_str, critical_str, off_str}};
+
+    explicit default_format_formatter(padding_info padinfo)
         : flag_formatter(padinfo) {}
 
-    void format(const details::log_msg &msg, const std::tm &tm_time, memory_buf_t &dest) override {
+    void format(const log_msg &msg, const std::tm &tm_time, memory_buf_t &dest) override {
         using std::chrono::duration_cast;
         using std::chrono::milliseconds;
         using std::chrono::seconds;
@@ -780,13 +808,13 @@ public:
             cache_timestamp_ = secs;
         }
         dest.append(cached_datetime_.begin(), cached_datetime_.end());
-
+        // append milliseconds
         auto millis = fmt_helper::time_fraction<milliseconds>(msg.time);
         fmt_helper::pad3(static_cast<uint32_t>(millis.count()), dest);
         dest.push_back(']');
         dest.push_back(' ');
 
-        // append logger name if exists
+        // append aligned logger name if exists
         if (!msg.logger_name.empty()) {
             dest.push_back('[');
             fmt_helper::append_string_view(msg.logger_name, dest);
@@ -794,14 +822,10 @@ public:
             dest.push_back(' ');
         }
 
-        dest.push_back('[');
+        // wrap the level name inside the [..] with color
-        // wrap the level name with color
+        msg.color_range_start = dest.size() + 1;  // +1 to start coloring after the '[';
-        msg.color_range_start = dest.size();
+        fmt_helper::append_string_view(padded_levels.at(static_cast<size_t>(msg.log_level)), dest);
-        // fmt_helper::append_string_view(level::to_c_str(msg.log_level), dest);
+        msg.color_range_end = dest.size() - 2;  // -2 to end coloring before the "] "
-        fmt_helper::append_string_view(to_string_view(msg.log_level), dest);
-        msg.color_range_end = dest.size();
-        dest.push_back(']');
-        dest.push_back(' ');
 
         // add source location if present
         if (!msg.source.empty()) {
@@ -844,7 +868,7 @@ pattern_formatter::pattern_formatter(pattern_time_type time_type, std::string eo
       need_localtime_{true},
       cached_tm_{},
       last_log_secs_{} {
-    formatters_.push_back(std::make_unique<details::full_formatter>(details::padding_info{}));
+    formatters_.push_back(std::make_unique<details::default_format_formatter>(details::padding_info{}));
 }
 
 std::unique_ptr<formatter> pattern_formatter::clone() const {
@@ -906,7 +930,7 @@ void pattern_formatter::handle_flag_(char flag, details::padding_info padding) {
     // process built-in flags
     switch (flag) {
         case ('+'):  // default formatter
-            formatters_.push_back(std::make_unique<details::full_formatter>(padding));
+            formatters_.push_back(std::make_unique<details::default_format_formatter>(padding));
             need_localtime_ = true;
             break;
 
@@ -1040,7 +1064,8 @@ void pattern_formatter::handle_flag_(char flag, details::padding_info padding) {
             break;
 
         case ('z'):  // timezone
-            formatters_.push_back(std::make_unique<details::z_formatter<Padder>>(padding));
+            formatters_.push_back(
+                std::make_unique<details::z_formatter<Padder>>(padding, pattern_time_type_));
             need_localtime_ = true;
             break;
 

src/sinks/ansicolor_sink.cpp

@@ -12,11 +12,8 @@ namespace spdlog {
 namespace sinks {
 
 template <typename Mutex>
-ansicolor_sink<Mutex>::ansicolor_sink(FILE *target_file, color_mode mode)
+ansicolor_sink<Mutex>::ansicolor_sink(FILE *target_file, color_mode mode) : target_file_(target_file) {
-    : target_file_(target_file)
+    set_color_mode_(mode);
-
-{
-    set_color_mode(mode);
     colors_.at(level_to_number(level::trace)) = to_string_(white);
     colors_.at(level_to_number(level::debug)) = to_string_(cyan);
     colors_.at(level_to_number(level::info)) = to_string_(green);
@@ -34,31 +31,36 @@ void ansicolor_sink<Mutex>::set_color(level color_level, string_view_t color) {
 
 template <typename Mutex>
 bool ansicolor_sink<Mutex>::should_color() const {
+    std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
     return should_do_colors_;
 }
 
 template <typename Mutex>
 void ansicolor_sink<Mutex>::set_color_mode(color_mode mode) {
+    std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
+    set_color_mode_(mode);
+}
+
+template <typename Mutex>
+void ansicolor_sink<Mutex>::set_color_mode_(color_mode mode) {
     switch (mode) {
         case color_mode::always:
             should_do_colors_ = true;
-            return;
+        return;
         case color_mode::automatic:
             should_do_colors_ = details::os::in_terminal(target_file_) && details::os::is_color_terminal();
-            return;
+        return;
         case color_mode::never:
             should_do_colors_ = false;
-            return;
+        return;
         default:
             should_do_colors_ = false;
     }
 }
-
 template <typename Mutex>
 void ansicolor_sink<Mutex>::sink_it_(const details::log_msg &msg) {
     // Wrap the originally formatted message in color codes.
     // If color is not supported in the terminal, log as is instead.
-
     msg.color_range_start = 0;
     msg.color_range_end = 0;
     memory_buf_t formatted;
@@ -85,12 +87,12 @@ void ansicolor_sink<Mutex>::flush_() {
 }
 
 template <typename Mutex>
-void ansicolor_sink<Mutex>::print_ccode_(const string_view_t color_code) {
+void ansicolor_sink<Mutex>::print_ccode_(const string_view_t color_code) const {
     details::os::fwrite_bytes(color_code.data(), color_code.size(), target_file_);
 }
 
 template <typename Mutex>
-void ansicolor_sink<Mutex>::print_range_(const memory_buf_t &formatted, size_t start, size_t end) {
+void ansicolor_sink<Mutex>::print_range_(const memory_buf_t &formatted, size_t start, size_t end) const {
     details::os::fwrite_bytes(formatted.data() + start, end - start, target_file_);
 }
 
@@ -109,12 +111,13 @@ template <typename Mutex>
 ansicolor_stderr_sink<Mutex>::ansicolor_stderr_sink(color_mode mode)
     : ansicolor_sink<Mutex>(stderr, mode) {}
 
-
 }  // namespace sinks
 }  // namespace spdlog
 
 // template instantiations
 #include "spdlog/details/null_mutex.h"
+template class SPDLOG_API spdlog::sinks::ansicolor_sink<std::mutex>;
+template class SPDLOG_API spdlog::sinks::ansicolor_sink<spdlog::details::null_mutex>;
 template class SPDLOG_API spdlog::sinks::ansicolor_stdout_sink<std::mutex>;
 template class SPDLOG_API spdlog::sinks::ansicolor_stdout_sink<spdlog::details::null_mutex>;
 template class SPDLOG_API spdlog::sinks::ansicolor_stderr_sink<std::mutex>;

src/sinks/async_sink.cpp

@@ -3,8 +3,10 @@
 
 #include "spdlog/sinks/async_sink.h"
 
+#include <algorithm>
 #include <cassert>
 #include <memory>
+#include <utility>
 
 #include "spdlog/common.h"
 #include "spdlog/details/mpmc_blocking_q.h"
@@ -19,6 +21,10 @@ async_sink::async_sink(config async_config)
     if (config_.queue_size == 0 || config_.queue_size > max_queue_size) {
         throw spdlog_ex("async_sink: invalid queue size");
     }
+    if (config_.custom_err_handler) {
+        err_helper_.set_err_handler(config_.custom_err_handler);
+    }
+
     q_ = std::make_unique<queue_t>(config_.queue_size);
     worker_thread_ = std::thread([this] {
         if (config_.on_thread_start) config_.on_thread_start();
@@ -32,13 +38,16 @@ async_sink::~async_sink() {
         q_->enqueue(async_log_msg(async_log_msg::type::terminate));
         worker_thread_.join();
     } catch (...) {
+        terminate_worker_ = true;  // as last resort, stop the worker thread using terminate_worker_ flag.
+#ifndef NDEBUG
         printf("Exception in ~async_sink()\n");
+#endif
     }
 }
 
-void async_sink::log(const details::log_msg &msg) { send_message_(async_log_msg::type::log, msg); }
+void async_sink::log(const details::log_msg &msg) { enqueue_message_(async_log_msg(async_log_msg::type::log, msg)); }
 
-void async_sink::flush() { send_message_(async_log_msg::type::flush, details::log_msg()); }
+void async_sink::flush() { enqueue_message_(details::async_log_msg(async_log_msg::type::flush)); }
 
 void async_sink::set_pattern(const std::string &pattern) { set_formatter(std::make_unique<pattern_formatter>(pattern)); }
 
@@ -54,6 +63,25 @@ void async_sink::set_formatter(std::unique_ptr<formatter> formatter) {
     }
 }
 
+bool async_sink::wait_all(const std::chrono::milliseconds timeout) const {
+    using std::chrono::steady_clock;
+    constexpr std::chrono::milliseconds sleep_duration(5);
+    const auto start_time = steady_clock::now();
+    while (q_->size() > 0) {
+        auto elapsed = steady_clock::now() - start_time;
+        if (elapsed > timeout) {
+            return false;
+        }
+        std::this_thread::sleep_for(std::min(sleep_duration, timeout));
+    }
+    return true;
+}
+
+void async_sink::wait_all() const {
+    while (!wait_all(std::chrono::milliseconds(10))) { /* empty */
+    }
+}
+
 size_t async_sink::get_overrun_counter() const { return q_->overrun_counter(); }
 
 void async_sink::reset_overrun_counter() const { q_->reset_overrun_counter(); }
@@ -65,16 +93,16 @@ void async_sink::reset_discard_counter() const { q_->reset_discard_counter(); }
 const async_sink::config &async_sink::get_config() const { return config_; }
 
 // private methods
-void async_sink::send_message_(async_log_msg::type msg_type, const details::log_msg &msg) const {
+void async_sink::enqueue_message_(details::async_log_msg &&msg) const {
     switch (config_.policy) {
         case overflow_policy::block:
-            q_->enqueue(async_log_msg(msg_type, msg));
+            q_->enqueue(std::move(msg));
             break;
         case overflow_policy::overrun_oldest:
-            q_->enqueue_nowait(async_log_msg(msg_type, msg));
+            q_->enqueue_nowait(std::move(msg));
             break;
         case overflow_policy::discard_new:
-            q_->enqueue_if_have_room(async_log_msg(msg_type, msg));
+            q_->enqueue_if_have_room(std::move(msg));
             break;
         default:
             assert(false);
@@ -84,7 +112,7 @@ void async_sink::send_message_(async_log_msg::type msg_type, const details::log_
 
 void async_sink::backend_loop_() {
     details::async_log_msg incoming_msg;
-    for (;;) {
+    while (!terminate_worker_) {
         q_->dequeue(incoming_msg);
         switch (incoming_msg.message_type()) {
             case async_log_msg::type::log:
@@ -101,7 +129,7 @@ void async_sink::backend_loop_() {
     }
 }
 
-void async_sink::backend_log_(const details::log_msg &msg)  {
+void async_sink::backend_log_(const details::log_msg &msg) {
     for (const auto &sink : config_.sinks) {
         if (sink->should_log(msg.log_level)) {
             try {

src/sinks/base_sink.cpp

@@ -5,6 +5,7 @@
 
 #include <memory>
 #include <mutex>
+
 #include "spdlog/common.h"
 #include "spdlog/pattern_formatter.h"
 
@@ -53,8 +54,8 @@ void base_sink<Mutex>::set_formatter_(std::unique_ptr<formatter> sink_formatter)
     formatter_ = std::move(sink_formatter);
 }
 
-} // namespace sinks
+}  // namespace sinks
-} // namespace spdlog
+}  // namespace spdlog
 
 // template instantiations
 #include "spdlog/details/null_mutex.h"

src/sinks/basic_file_sink.cpp

@@ -2,9 +2,11 @@
 // Distributed under the MIT License (http://opensource.org/licenses/MIT)
 
 #include "spdlog/sinks/basic_file_sink.h"
-#include "spdlog/common.h"
+
 #include <mutex>
 
+#include "spdlog/common.h"
+
 namespace spdlog {
 namespace sinks {
 
@@ -19,6 +21,12 @@ const filename_t &basic_file_sink<Mutex>::filename() const {
     return file_helper_.filename();
 }
 
+template <typename Mutex>
+void basic_file_sink<Mutex>::truncate() {
+    std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
+    file_helper_.reopen(true);
+}
+
 template <typename Mutex>
 void basic_file_sink<Mutex>::sink_it_(const details::log_msg &msg) {
     memory_buf_t formatted;
@@ -34,7 +42,6 @@ void basic_file_sink<Mutex>::flush_() {
 }  // namespace sinks
 }  // namespace spdlog
 
-
 // template instantiations
 #include "spdlog/details/null_mutex.h"
 template class SPDLOG_API spdlog::sinks::basic_file_sink<std::mutex>;

src/sinks/rotating_file_sink.cpp

@@ -65,6 +65,7 @@ filename_t rotating_file_sink<Mutex>::filename() {
 
 template <typename Mutex>
 void rotating_file_sink<Mutex>::rotate_now() {
+    std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
     rotate_();
 }
 
@@ -142,4 +143,4 @@ bool rotating_file_sink<Mutex>::rename_file_(const filename_t &src_filename, con
 // template instantiations
 #include "spdlog/details/null_mutex.h"
 template class SPDLOG_API spdlog::sinks::rotating_file_sink<std::mutex>;
-template class SPDLOG_API spdlog::sinks::rotating_file_sink<spdlog::details::null_mutex>;
+template class SPDLOG_API spdlog::sinks::rotating_file_sink<spdlog::details::null_mutex>;

src/sinks/wincolor_sink.cpp

@@ -8,7 +8,9 @@
 
 // clang-format on
 #include "spdlog/sinks/wincolor_sink.h"
+
 #include "spdlog/common.h"
+#include "spdlog/details/os.h"
 
 namespace spdlog {
 namespace sinks {
@@ -107,8 +109,15 @@ std::uint16_t wincolor_sink<Mutex>::set_foreground_color_(std::uint16_t attribs)
 template <typename Mutex>
 void wincolor_sink<Mutex>::print_range_(const memory_buf_t &formatted, size_t start, size_t end) {
     if (end > start) {
+#if defined(SPDLOG_UTF8_TO_WCHAR_CONSOLE)
+        wmemory_buf_t wformatted;
+        details::os::utf8_to_wstrbuf(string_view_t(formatted.data() + start, end - start), wformatted);
+        auto size = static_cast<DWORD>(wformatted.size());
+        auto ignored = ::WriteConsoleW(static_cast<HANDLE>(out_handle_), wformatted.data(), size, nullptr, nullptr);
+#else
         auto size = static_cast<DWORD>(end - start);
         auto ignored = ::WriteConsoleA(static_cast<HANDLE>(out_handle_), formatted.data() + start, size, nullptr, nullptr);
+#endif
         (void)(ignored);
     }
 }
@@ -131,7 +140,6 @@ template <typename Mutex>
 wincolor_stderr_sink<Mutex>::wincolor_stderr_sink(color_mode mode)
     : wincolor_sink<Mutex>(::GetStdHandle(STD_ERROR_HANDLE), mode) {}
 
-
 }  // namespace sinks
 }  // namespace spdlog
 

src/spdlog.cpp

@@ -13,21 +13,17 @@
 
 namespace spdlog {
 
-
 #ifndef SPDLOG_DISABLE_GLOBAL_LOGGER
-    static std::shared_ptr<logger> s_logger = std::make_shared<logger>("global", std::make_shared<sinks::stdout_color_sink_mt>());
+static std::shared_ptr<logger> s_logger = std::make_shared<logger>("", std::make_shared<sinks::stdout_color_sink_mt>());
 #else
-    static std::short_ptr<logger> s_logger = nullptr;
+static std::short_ptr<logger> s_logger = nullptr;
 #endif
 
-
 std::shared_ptr<logger> global_logger() { return s_logger; }
 
 void set_global_logger(std::shared_ptr<logger> global_logger) { s_logger = std::move(global_logger); }
 
-logger *global_logger_raw() noexcept {
+logger *global_logger_raw() noexcept { return s_logger.get(); }
-    return s_logger.get();
-}
 
 void set_formatter(std::unique_ptr<formatter> formatter) { global_logger()->set_formatter(std::move(formatter)); }
 
@@ -37,7 +33,7 @@ void set_pattern(std::string pattern, pattern_time_type time_type) {
 
 level get_level() { return global_logger()->log_level(); }
 
-bool should_log(level level) { return global_logger()->should_log(level); }
+bool should_log(level log_level) { return global_logger()->should_log(log_level); }
 
 void set_level(level level) { global_logger()->set_level(level); }
 

tests/CMakeLists.txt

@@ -52,6 +52,7 @@ set(SPDLOG_UTESTS_SOURCES
     test_log_level.cpp
     test_include_sinks.cpp
     test_bin_to_hex.cpp
+    test_timezone.cpp
     test_errors.cpp)
 
 if(WIN32)

tests/includes.h

@@ -25,6 +25,9 @@
 
 #define SPDLOG_ACTIVE_LEVEL SPDLOG_LEVEL_DEBUG
 
+#undef SPDLOG_LEVEL_NAMES
+#undef SPDLOG_SHORT_LEVEL_NAMES
+
 #include "spdlog/details/fmt_helper.h"
 #include "spdlog/pattern_formatter.h"
 #include "spdlog/sinks/null_sink.h"

tests/test_async.cpp

@@ -10,6 +10,7 @@
 using spdlog::sinks::async_sink;
 using spdlog::sinks::sink;
 using spdlog::sinks::test_sink_mt;
+using namespace std::chrono_literals;
 
 auto creat_async_logger(size_t queue_size, std::shared_ptr<sink> backend_sink) {
     async_sink::config cfg;
@@ -41,7 +42,7 @@ TEST_CASE("basic async test ", "[async]") {
 
 TEST_CASE("discard policy ", "[async]") {
     auto test_sink = std::make_shared<test_sink_mt>();
-    test_sink->set_delay(std::chrono::milliseconds(1));
+    test_sink->set_delay(1ms);
     async_sink::config config;
     config.queue_size = 4;
     config.policy = async_sink::overflow_policy::overrun_oldest;
@@ -62,7 +63,7 @@ TEST_CASE("discard policy ", "[async]") {
 
 TEST_CASE("discard policy discard_new ", "[async]") {
     auto test_sink = std::make_shared<test_sink_mt>();
-    test_sink->set_delay(std::chrono::milliseconds(1));
+    test_sink->set_delay(1ms);
     async_sink::config config;
     config.queue_size = 4;
     config.policy = async_sink::overflow_policy::discard_new;
@@ -71,7 +72,6 @@ TEST_CASE("discard policy discard_new ", "[async]") {
     auto as = std::make_shared<async_sink>(config);
     auto logger = std::make_shared<spdlog::logger>("async_logger", as);
 
-
     REQUIRE(as->get_config().policy == async_sink::overflow_policy::discard_new);
     REQUIRE(as->get_discard_counter() == 0);
     REQUIRE(as->get_overrun_counter() == 0);
@@ -95,14 +95,13 @@ TEST_CASE("flush", "[async]") {
         }
         logger->flush();
     }
-    // std::this_thread::sleep_for(std::chrono::milliseconds(250));
     REQUIRE(test_sink->msg_counter() == messages);
     REQUIRE(test_sink->flush_counter() == 1);
 }
 
 TEST_CASE("wait_dtor ", "[async]") {
     auto test_sink = std::make_shared<test_sink_mt>();
-    test_sink->set_delay(std::chrono::milliseconds(5));
+    test_sink->set_delay(5ms);
     async_sink::config config;
     config.sinks.push_back(test_sink);
     config.queue_size = 4;
@@ -167,7 +166,6 @@ TEST_CASE("to_file", "[async]") {
     REQUIRE(ends_with(contents, spdlog::fmt_lib::format("Hello message #1023{}", default_eol)));
 }
 
-
 TEST_CASE("bad_ctor", "[async]") {
     async_sink::config cfg;
     cfg.queue_size = 0;
@@ -295,3 +293,63 @@ TEST_CASE("backend_ex", "[async]") {
     REQUIRE_NOTHROW(logger->info("Hello message"));
     REQUIRE_NOTHROW(logger->flush());
 }
+
+// test async custom error handler. trigger it using a backend exception and make sure it's called
+TEST_CASE("custom_err_handler", "[async]") {
+    bool error_called = false;
+    auto test_sink = std::make_shared<test_sink_mt>();
+    test_sink->set_exception(std::runtime_error("test backend exception"));
+    async_sink::config config;
+    config.sinks.push_back(std::move(test_sink));
+    config.custom_err_handler = [&error_called](const std::string &) { error_called = true; };
+    auto asink = std::make_shared<async_sink>(config);
+    spdlog::logger("async_logger", std::move(asink)).info("Test");
+    // lvalue logger so will be destructed here already so all messages were processed
+    REQUIRE(error_called);
+}
+
+// test wait_all
+TEST_CASE("wait_all", "[async]") {
+    auto test_sink = std::make_shared<test_sink_mt>();
+    auto delay = 10ms;
+    test_sink->set_delay(delay);
+    async_sink::config config;
+    config.sinks.push_back(test_sink);
+    size_t messages = 10;
+    auto as = std::make_shared<async_sink>(config);
+    auto logger = std::make_shared<spdlog::logger>("async_logger", as);
+    for (size_t i = 0; i < messages; i++) {
+        logger->info("Hello message");
+    }
+    REQUIRE_FALSE(as->wait_all(-10ms));
+    REQUIRE_FALSE(as->wait_all(0ms));
+    auto start = std::chrono::steady_clock::now();
+    REQUIRE_FALSE(as->wait_all(delay));
+
+    // should have waited approx 10ms before giving up
+    auto elapsed = std::chrono::steady_clock::now() - start;
+    REQUIRE(elapsed >= delay);
+    REQUIRE(elapsed < delay *  6); // big tolerance, to pass tests in slow virtual machines
+    // wait enough time for all messages to be processed
+    REQUIRE(as->wait_all(messages * delay + 500ms));
+    REQUIRE(as->wait_all(-10ms));  // no more messages
+    REQUIRE(as->wait_all(0ms));    // no more messages
+    REQUIRE(as->wait_all(10ms));   // no more messages
+}
+
+// test wait_all without timeout
+TEST_CASE("wait_all2", "[async]") {
+    auto test_sink = std::make_shared<test_sink_mt>();
+    auto delay = 10ms;
+    test_sink->set_delay(delay);
+    async_sink::config config;
+    config.sinks.push_back(test_sink);
+    size_t messages = 10;
+    auto as = std::make_shared<async_sink>(config);
+    auto logger = std::make_shared<spdlog::logger>("async_logger", as);
+    for (size_t i = 0; i < messages; i++) {
+        logger->info("Hello message");
+    }
+    as->wait_all();
+    REQUIRE(test_sink->msg_counter() == messages);
+}

tests/test_custom_callbacks.cpp

@@ -3,6 +3,9 @@
  * https://raw.githubusercontent.com/gabime/spdlog/v2.x/LICENSE
  */
 #include "includes.h"
+
+#include <iterator>
+
 #include "spdlog/common.h"
 #include "spdlog/sinks/callback_sink.h"
 #include "test_sink.h"
@@ -14,7 +17,8 @@ TEST_CASE("custom_callback_logger", "[custom_callback_logger]") {
         spdlog::memory_buf_t formatted;
         formatter.format(msg, formatted);
         auto eol_len = strlen(spdlog::details::os::default_eol);
-        lines.emplace_back(formatted.begin(), formatted.end() - eol_len);
+        using diff_t = typename std::iterator_traits<decltype(formatted.end())>::difference_type;
+        lines.emplace_back(formatted.begin(), formatted.end() - static_cast<diff_t>(eol_len));
     });
     std::shared_ptr<spdlog::sinks::test_sink_st> test_sink(new spdlog::sinks::test_sink_st);
 

tests/test_dup_filter.cpp

@@ -80,3 +80,41 @@ TEST_CASE("dup_filter_test5", "[dup_filter_sink]") {
     REQUIRE(test_sink->msg_counter() == 3);  // skip 2 messages but log the "skipped.." message before message2
     REQUIRE(test_sink->lines()[1] == "Skipped 2 duplicate messages..");
 }
+
+TEST_CASE("dup_filter_skipped_notification_uses_last_duplicate_level", "[dup_filter_sink]") {
+    using spdlog::sinks::dup_filter_sink_st;
+    using spdlog::sinks::test_sink_mt;
+
+    dup_filter_sink_st dup_sink{std::chrono::seconds{5}};
+    auto test_sink = std::make_shared<test_sink_mt>();
+    test_sink->set_pattern("%L");
+    dup_sink.add_sink(test_sink);
+
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::warn, "same"});
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::warn, "same"});
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::info, "diff"});
+
+    REQUIRE(test_sink->lines().size() == 3);
+    REQUIRE(test_sink->lines()[0] == "W");
+    REQUIRE(test_sink->lines()[1] == "W");
+    REQUIRE(test_sink->lines()[2] == "I");
+}
+
+TEST_CASE("dup_filter_skipped_notification_fixed_level", "[dup_filter_sink]") {
+    using spdlog::sinks::dup_filter_sink_st;
+    using spdlog::sinks::test_sink_mt;
+
+    dup_filter_sink_st dup_sink{std::chrono::seconds{5}, spdlog::level::info};
+    auto test_sink = std::make_shared<test_sink_mt>();
+    test_sink->set_pattern("%L");
+    dup_sink.add_sink(test_sink);
+
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::warn, "same"});
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::warn, "same"});
+    dup_sink.log(spdlog::details::log_msg{"test", spdlog::level::info, "diff"});
+
+    REQUIRE(test_sink->lines().size() == 3);
+    REQUIRE(test_sink->lines()[0] == "W");
+    REQUIRE(test_sink->lines()[1] == "I");
+    REQUIRE(test_sink->lines()[2] == "I");
+}

tests/test_errors.cpp

@@ -18,11 +18,10 @@ protected:
 };
 struct custom_ex {};
 
-
 using namespace spdlog::sinks;
 TEST_CASE("default_error_handler", "[errors]") {
     prepare_logdir();
-    auto logger = spdlog::create<basic_file_sink_mt>("test-error", log_filename);
+    auto logger = spdlog::create<basic_file_sink_mt>("test-bad-format", log_filename);
     logger->set_pattern("%v");
     logger->info(SPDLOG_FMT_RUNTIME("Test message {} {}"), 1);
     logger->info("Test message {}", 2);
@@ -36,17 +35,43 @@ TEST_CASE("custom_error_handler", "[errors]") {
     prepare_logdir();
     auto logger = spdlog::create<basic_file_sink_mt>("test-format-error", log_filename);
     logger->flush_on(spdlog::level::info);
-    logger->set_error_handler([=](const std::string & msg) {
+    logger->set_error_handler([=](const std::string &msg) { REQUIRE(msg == "argument not found"); });
-        REQUIRE(msg == "argument not found");
-    });
     logger->info("Good message #1");
     REQUIRE_NOTHROW(logger->info(SPDLOG_FMT_RUNTIME("Bad format msg {} {}"), "xxx"));
     logger->info("Good message #2");
     require_message_count(log_filename, 2);
 }
 
-TEST_CASE("default_error_handler2", "[errors]") {
+TEST_CASE("throwing_sink", "[errors]") {
-    auto logger = std::make_shared<spdlog::logger>("test-failing-sink", std::make_shared<failing_sink>());
+    auto logger = std::make_shared<spdlog::logger>("test-throwing-sink", std::make_shared<failing_sink>());
+    REQUIRE_NOTHROW(logger->info("Some message"));
+}
+
+TEST_CASE("throwing_flush", "[errors]") {
+    auto logger = spdlog::create<failing_sink>("test-throwing-sink");
+    REQUIRE_NOTHROW(logger->flush());
+}
+
+TEST_CASE("throwing_error_handler", "[errors]") {
+    auto logger = std::make_shared<spdlog::logger>("test-throwing-error-handler", std::make_shared<failing_sink>());
+    logger->set_error_handler([=](const std::string &msg) {
+        REQUIRE(msg == log_err_msg);
+        throw std::runtime_error("test throw");
+    });
+    REQUIRE_NOTHROW(logger->info("Some message"));
+}
+
+TEST_CASE("throwing_flush_error_handler", "[errors]") {
+    auto logger = spdlog::create<failing_sink>("test-throwing-error-handler");
+    logger->set_error_handler([=](const std::string &msg) {
+        REQUIRE(msg == flush_err_msg);
+        throw std::runtime_error("test throw");
+    });
+    REQUIRE_NOTHROW(logger->flush());
+}
+
+TEST_CASE("unknown_ex_from_err_handler", "[errors]") {
+    auto logger = std::make_shared<spdlog::logger>("test-throwing-error-handler", std::make_shared<failing_sink>());
     logger->set_error_handler([=](const std::string &msg) {
         REQUIRE(msg == log_err_msg);
         throw custom_ex();
@@ -54,8 +79,8 @@ TEST_CASE("default_error_handler2", "[errors]") {
     REQUIRE_NOTHROW(logger->info("Some message"));
 }
 
-TEST_CASE("flush_error_handler", "[errors]") {
+TEST_CASE("unknown_ex_from_flush_err_handler", "[errors]") {
-    auto logger = spdlog::create<failing_sink>("test-failing-sink");
+    auto logger = spdlog::create<failing_sink>("test-throwing-error-handler");
     logger->set_error_handler([=](const std::string &msg) {
         REQUIRE(msg == flush_err_msg);
         throw custom_ex();

tests/test_file_logging.cpp

@@ -41,6 +41,26 @@ TEST_CASE("flush_on", "[flush_on]") {
                                                                  default_eol, default_eol, default_eol));
 }
 
+TEST_CASE("basic_file_sink_truncate", "[truncate]") {
+    prepare_logdir();
+    const spdlog::filename_t filename = SPDLOG_FILENAME_T(SIMPLE_LOG);
+    const bool truncate = true;
+    const auto sink = std::make_shared<basic_file_sink_mt>(filename, truncate);
+    const auto logger = std::make_shared<spdlog::logger>("simple_file_logger", sink);
+
+    logger->info("Test message {}", 3.14);
+    logger->info("Test message {}", 2.71);
+    logger->flush();
+    REQUIRE(count_lines(SIMPLE_LOG) == 2);
+
+    sink->truncate();
+    REQUIRE(count_lines(SIMPLE_LOG) == 0);
+
+    logger->info("Test message {}", 6.28);
+    logger->flush();
+    REQUIRE(count_lines(SIMPLE_LOG) == 1);
+}
+
 TEST_CASE("rotating_file_logger1", "[rotating_logger]") {
     prepare_logdir();
     size_t max_size = 1024 * 10;

tests/test_misc.cpp

@@ -7,8 +7,8 @@
 
 #include "includes.h"
 #include "spdlog/details/os.h"
-#include "spdlog/sinks/ostream_sink.h"
 #include "spdlog/sinks/async_sink.h"
+#include "spdlog/sinks/ostream_sink.h"
 #include "test_sink.h"
 
 template <class T>
@@ -72,6 +72,78 @@ TEST_CASE("to_level_enum", "[convert_to_level_enum]") {
     REQUIRE(spdlog::level_from_str("critical") == spdlog::level::critical);
     REQUIRE(spdlog::level_from_str("off") == spdlog::level::off);
     REQUIRE(spdlog::level_from_str("null") == spdlog::level::off);
+    REQUIRE(spdlog::level_from_str("TRACE") == spdlog::level::trace);
+    REQUIRE(spdlog::level_from_str("DEBUG") == spdlog::level::debug);
+    REQUIRE(spdlog::level_from_str("INFO") == spdlog::level::info);
+    REQUIRE(spdlog::level_from_str("WARNING") == spdlog::level::warn);
+    REQUIRE(spdlog::level_from_str("WARN") == spdlog::level::warn);
+    REQUIRE(spdlog::level_from_str("ERROR") == spdlog::level::err);
+    REQUIRE(spdlog::level_from_str("ERR") == spdlog::level::err);
+    REQUIRE(spdlog::level_from_str("CRITICAL") == spdlog::level::critical);
+    REQUIRE(spdlog::level_from_str("OFF") == spdlog::level::off);
+    REQUIRE(spdlog::level_from_str("TrAcE") == spdlog::level::trace);
+    REQUIRE(spdlog::level_from_str("DeBuG") == spdlog::level::debug);
+}
+
+TEST_CASE("copy_ctor", "[copy_ctor]") {
+    using spdlog::sinks::test_sink_mt;
+    auto test_sink = std::make_shared<test_sink_mt>();
+    auto logger = std::make_shared<spdlog::logger>("orig", test_sink);
+    logger->set_pattern("%v");
+    bool error_handled = false;
+    logger->set_error_handler([&error_handled](const std::string&) { error_handled = true; });
+    spdlog::logger copied = *logger;
+
+    REQUIRE(copied.name() == logger->name());
+    REQUIRE(logger->sinks() == copied.sinks());
+    REQUIRE(logger->log_level() == copied.log_level());
+    REQUIRE(logger->flush_level() == copied.flush_level());
+
+    logger->info("Some message 1");
+    copied.info("Some message 2");
+
+    REQUIRE(test_sink->lines().size() == 2);
+    REQUIRE(test_sink->lines()[0] == "Some message 1");
+    REQUIRE(test_sink->lines()[1] == "Some message 2");
+
+    // check that copied custom error handler was indeed copied
+    test_sink->set_exception(std::runtime_error("Some error"));
+    REQUIRE(error_handled == false);
+    copied.error("Some error");
+    REQUIRE(error_handled == true);
+}
+
+TEST_CASE("move_ctor", "[move_ctor]") {
+    auto log_level = spdlog::level::critical;
+    auto flush_level = spdlog::level::warn;
+    using spdlog::sinks::test_sink_mt;
+    auto test_sink = std::make_shared<test_sink_mt>();
+    auto logger = std::make_shared<spdlog::logger>("orig", test_sink);
+    logger->flush_on(flush_level);
+    logger->set_level(log_level);
+    logger->set_pattern("%v");
+    bool error_handled = false;
+    logger->set_error_handler([&error_handled](const std::string&) { error_handled = true; });
+    spdlog::logger moved = std::move(*logger);
+
+    REQUIRE(logger->name() == "");
+    REQUIRE(logger->sinks().empty());
+    REQUIRE(moved.name() == "orig");
+    REQUIRE(moved.sinks()[0].get() == test_sink.get());
+    REQUIRE(moved.log_level() == log_level);
+    REQUIRE(moved.flush_level() == flush_level);
+
+    logger->critical("Some message 1");
+    moved.critical("Some message 2");
+
+    REQUIRE(test_sink->lines().size() == 1);
+    REQUIRE(test_sink->lines()[0] == "Some message 2");
+
+    // check that copied custom error handler was indeed copied
+    test_sink->set_exception(std::runtime_error("Some error"));
+    REQUIRE(error_handled == false);
+    moved.critical("Some error");
+    REQUIRE(error_handled == true);
 }
 
 TEST_CASE("clone-logger", "[clone]") {
@@ -79,18 +151,27 @@ TEST_CASE("clone-logger", "[clone]") {
     auto test_sink = std::make_shared<test_sink_mt>();
     auto logger = std::make_shared<spdlog::logger>("orig", test_sink);
     logger->set_pattern("%v");
+    bool error_handled = false;
+    logger->set_error_handler([&error_handled](const std::string&) { error_handled = true; });
     auto cloned = logger->clone("clone");
 
     REQUIRE(cloned->name() == "clone");
     REQUIRE(logger->sinks() == cloned->sinks());
     REQUIRE(logger->log_level() == cloned->log_level());
     REQUIRE(logger->flush_level() == cloned->flush_level());
+
     logger->info("Some message 1");
     cloned->info("Some message 2");
 
     REQUIRE(test_sink->lines().size() == 2);
     REQUIRE(test_sink->lines()[0] == "Some message 1");
     REQUIRE(test_sink->lines()[1] == "Some message 2");
+
+    // check that cloned custom error handler was indeed cloned
+    test_sink->set_exception(std::runtime_error("Some error"));
+    REQUIRE(error_handled == false);
+    cloned->error("Some error");
+    REQUIRE(error_handled == true);
 }
 
 TEST_CASE("clone async", "[clone]") {

tests/test_pattern_formatter.cpp

@@ -2,6 +2,9 @@
 #include "spdlog/sinks/ostream_sink.h"
 #include "test_sink.h"
 
+#include <chrono>
+#include <regex>
+
 using spdlog::memory_buf_t;
 
 // log to str and return it
@@ -18,6 +21,21 @@ static std::string log_to_str(const std::string &msg, const Args &...args) {
     return oss.str();
 }
 
+// log to str and return it with time
+template <typename... Args>
+static std::string log_to_str_with_time(spdlog::log_clock::time_point log_time, const std::string &msg, const Args &...args) {
+    std::ostringstream oss;
+    auto oss_sink = std::make_shared<spdlog::sinks::ostream_sink_mt>(oss);
+    spdlog::logger oss_logger("pattern_tester", oss_sink);
+    oss_logger.set_level(spdlog::level::info);
+
+    oss_logger.set_formatter(
+        std::unique_ptr<spdlog::formatter>(new spdlog::pattern_formatter(args...)));
+
+    oss_logger.log(log_time, {}, spdlog::level::info, msg);
+    return oss.str();
+}
+
 TEST_CASE("custom eol", "[pattern_formatter]") {
     std::string msg = "Hello custom eol test";
     std::string eol = ";)";
@@ -52,6 +70,36 @@ TEST_CASE("date MM/DD/YY ", "[pattern_formatter]") {
     REQUIRE(log_to_str("Some message", "%D %v", spdlog::pattern_time_type::local, "\n") == oss.str());
 }
 
+TEST_CASE("%z with UTC pattern time", "[pattern_formatter]") {
+    using namespace std::chrono_literals;
+    const auto now = std::chrono::system_clock::now();
+    const auto yesterday = now - 24h;
+
+#ifndef SPDLOG_NO_TZ_OFFSET
+    REQUIRE(log_to_str_with_time(yesterday, "Some message", "%z", spdlog::pattern_time_type::utc, "\n") ==
+            "+00:00\n");
+#else
+    REQUIRE(log_to_str_with_time(yesterday, "Some message", "%z", spdlog::pattern_time_type::utc, "\n") ==
+            "+??:??\n");
+#endif
+}
+
+// see test_timezone.cpp for actual UTC offset calculation tests
+TEST_CASE("UTC offset", "[pattern_formatter]") {
+    using namespace std::chrono_literals;
+    const auto now = std::chrono::system_clock::now();
+    std::string result =
+        log_to_str_with_time(now, "Some message", "%z", spdlog::pattern_time_type::local, "\n");
+
+#ifndef SPDLOG_NO_TZ_OFFSET
+    // Match format: +HH:MM or -HH:MM
+    std::regex re(R"([+-]\d{2}:[0-5]\d\n)");
+    REQUIRE(std::regex_match(result, re));
+#else
+    REQUIRE(result == "+??:??\n");
+#endif
+}
+
 TEST_CASE("color range test1", "[pattern_formatter]") {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("%^%v%$", spdlog::pattern_time_type::local, "\n");
 

tests/test_ringbuffer_sink.cpp

@@ -57,15 +57,5 @@ TEST_CASE("test_empty", "[ringbuffer_sink]") {
 }
 
 TEST_CASE("test_empty_size", "[ringbuffer_sink]") {
-    const size_t sink_size = 0;
+    REQUIRE_THROWS_AS((void)spdlog::sinks::ringbuffer_sink_mt(0), spdlog::spdlog_ex);
-    auto sink = std::make_shared<spdlog::sinks::ringbuffer_sink_mt>(sink_size);
-    spdlog::logger l("logger", sink);
-
-    for (size_t i = 0; i < sink_size + 1; ++i) {
-        l.info("{}", i);
-    }
-
-    sink->drain([&](std::string_view) {
-        REQUIRE_FALSE(true);  // should not be called since the sink size is 0
-    });
 }

tests/test_sink.h

@@ -6,9 +6,10 @@
 #pragma once
 
 #include <chrono>
+#include <exception>
+#include <iterator>
 #include <mutex>
 #include <thread>
-#include <exception>
 
 #include "spdlog/details/null_mutex.h"
 #include "spdlog/details/os.h"
@@ -37,13 +38,9 @@ public:
         delay_ = delay;
     }
 
-    void set_exception(const std::runtime_error& ex) {
+    void set_exception(const std::runtime_error& ex) { exception_ptr_ = std::make_exception_ptr(ex); }
-        exception_ptr_ = std::make_exception_ptr(ex);
-    }
 
-    void clear_exception() {
+    void clear_exception() { exception_ptr_ = nullptr; }
-        exception_ptr_ = nullptr;
-    }
 
     // return last output without the eol
     std::vector<std::string> lines() {
@@ -52,7 +49,7 @@ public:
     }
 
 protected:
-    void sink_it_(const details::log_msg &msg) override {
+    void sink_it_(const details::log_msg& msg) override {
         if (exception_ptr_) {
             std::rethrow_exception(exception_ptr_);
         }
@@ -61,7 +58,8 @@ protected:
         // save the line without the eol
         auto eol_len = strlen(details::os::default_eol);
         if (lines_.size() < lines_to_save) {
-            lines_.emplace_back(formatted.begin(), formatted.end() - eol_len);
+            using diff_t = typename std::iterator_traits<decltype(formatted.end())>::difference_type;
+            lines_.emplace_back(formatted.begin(), formatted.end() - static_cast<diff_t>(eol_len));
         }
         msg_counter_++;
         std::this_thread::sleep_for(delay_);
@@ -78,7 +76,7 @@ protected:
     size_t flush_counter_{0};
     std::chrono::milliseconds delay_{std::chrono::milliseconds::zero()};
     std::vector<std::string> lines_;
-    std::exception_ptr exception_ptr_; // will be thrown on next log or flush if not null
+    std::exception_ptr exception_ptr_;  // will be thrown on next log or flush if not null
 };
 
 using test_sink_mt = test_sink<std::mutex>;

tests/test_stopwatch.cpp

@@ -5,7 +5,7 @@
 TEST_CASE("stopwatch1", "[stopwatch]") {
     using std::chrono::milliseconds;
     using clock = std::chrono::steady_clock;
-    milliseconds wait_ms(200);
+    milliseconds wait_ms(500);
     milliseconds tolerance_ms(250);
     auto start = clock::now();
     spdlog::stopwatch sw;
@@ -22,7 +22,7 @@ TEST_CASE("stopwatch2", "[stopwatch]") {
     using std::chrono::milliseconds;
     using clock = std::chrono::steady_clock;
 
-    clock::duration wait_duration(milliseconds(200));
+    clock::duration wait_duration(milliseconds(500));
     clock::duration tolerance_duration(milliseconds(250));
 
     auto test_sink = std::make_shared<test_sink_st>();

tests/test_timezone.cpp

@@ -0,0 +1,194 @@
+#ifndef SPDLOG_NO_TZ_OFFSET
+
+#include "includes.h"
+#include <ctime>
+#include <cstdlib>
+#include <cstring>
+
+// Helper to construct a simple std::tm from components
+std::tm make_tm(int year, int month, int day, int hour, int minute) {
+    std::tm t;
+    std::memset(&t, 0, sizeof(t));
+    t.tm_year = year - 1900;
+    t.tm_mon = month - 1;
+    t.tm_mday = day;
+    t.tm_hour = hour;
+    t.tm_min = minute;
+    t.tm_sec = 0;
+    t.tm_isdst = -1;
+    std::mktime(&t);
+    return t;
+}
+
+// Cross-platform RAII Helper to safely set/restore process timezone
+class ScopedTZ {
+    std::string original_tz_;
+    bool has_original_ = false;
+
+public:
+    explicit ScopedTZ(const std::string &tz_name) {
+        // save current TZ
+#ifdef _WIN32
+        char *buf = nullptr;
+        size_t len = 0;
+        if (_dupenv_s(&buf, &len, "TZ") == 0 && buf != nullptr) {
+            original_tz_ = std::string(buf);
+            has_original_ = true;
+            free(buf);
+        }
+#else
+        const char *tz = std::getenv("TZ");
+        if (tz) {
+            original_tz_ = tz;
+            has_original_ = true;
+        }
+#endif
+
+        // set new TZ
+#ifdef _WIN32
+        _putenv_s("TZ", tz_name.c_str());
+        _tzset();
+#else
+        setenv("TZ", tz_name.c_str(), 1);
+        tzset();
+#endif
+    }
+
+    ~ScopedTZ() {
+        // restore original TZ
+#ifdef _WIN32
+        if (has_original_) {
+            _putenv_s("TZ", original_tz_.c_str());
+        } else {
+            _putenv_s("TZ", "");
+        }
+        _tzset();
+#else
+        if (has_original_) {
+            setenv("TZ", original_tz_.c_str(), 1);
+        } else {
+            unsetenv("TZ");
+        }
+        tzset();
+#endif
+    }
+};
+
+using spdlog::details::os::utc_minutes_offset;
+
+/*
+ * POSIX 2024 defines three formats for the TZ environment variable,
+ *
+ * 1. Implementation defined format which always starts with a colon:
+ *    ":characters".
+ * 2. A specifier which fully describes the timezone rule in format
+ *    "stdoffset[dst[offset][,start[/time],end[/time]]]". Note the
+ *    offset and start/end part could be omitted, in which case one hour
+ *    is implied, or it's considered implementation-defined when changing
+ *    to and from Daylight Saving Time occurs.
+ * 3. Geographical or special timezone from an implementation-defined
+ *    timezone database.
+ *
+ * On POSIX-compilant systems, we prefer format 2, and explicitly specify the
+ * DST rules to avoid implementation-defined behavior.
+ *
+ * See also IEEE 1003.1-2024 8.3 Other Environment Variables.
+ */
+#ifndef _WIN32
+/*
+ * Standard time is UTC-5 ("EST"), DST time is UTC-4 ("EDT"). DST is active
+ * from 2:00 on the 2nd Sunday in March, to 2:00 on 1st Sunday in November.
+ */
+#define EST5EDT "EST5EDT,M3.2.0,M11.1.0"
+/*
+ * Standard time is UTC+2 ("IST"), DST time is UTC+3 ("IDT"). DST is active
+ * from 2:00 on following day of the 4th Thursday in March, to 2:00 on the
+ * last Sunday in October.
+ */
+#define IST_MINUS2_IDT "IST-2IDT,M3.4.4/26,M10.5.0"
+#else
+/*
+ * However, Windows doesn't follow the POSIX rules and only accept a TZ
+ * environment variable in format
+ *
+ *   tzn [+|-]hh[:mm[:ss] ][dzn]
+ *
+ * thus we couldn't specify the DST rules. Luckily, Windows C runtime library
+ * assumes the United State's rules for implementing the calculation of DST,
+ * which is fine for our test cases.
+ *
+ * See also https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset?view=msvc-170
+ */
+#define EST5EDT "EST5EDT"
+#define IST_MINUS2_IDT "IST-2IDT"
+#endif
+
+TEST_CASE("UTC Offset - Western Hemisphere (USA - Standard Time)", "[timezone][west]") {
+    // EST5EDT: Eastern Standard Time (UTC-5)
+    ScopedTZ tz(EST5EDT);
+
+    // Jan 15th (Winter)
+    auto tm = make_tm(2023, 1, 15, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == -300);
+}
+
+TEST_CASE("UTC Offset - Eastern Hemisphere (Europe/Israel - Standard Time)", "[timezone][east]") {
+    // IST-2IDT: Israel Standard Time (UTC+2)
+    ScopedTZ tz(IST_MINUS2_IDT);
+
+    // Jan 15th (Winter)
+    auto tm = make_tm(2023, 1, 15, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == 120);
+}
+
+TEST_CASE("UTC Offset - Zero Offset (UTC/GMT)", "[timezone][utc]") {
+    ScopedTZ tz("GMT0");
+
+    // Check Winter
+    auto tm_winter = make_tm(2023, 1, 15, 12, 0);
+    REQUIRE(utc_minutes_offset(tm_winter) == 0);
+
+    // Check Summer (GMT never shifts, so this should also be 0)
+    auto tm_summer = make_tm(2023, 7, 15, 12, 0);
+    REQUIRE(utc_minutes_offset(tm_summer) == 0);
+}
+
+TEST_CASE("UTC Offset - Non-Integer Hour Offsets (India)", "[timezone][partial]") {
+    // IST-5:30: India Standard Time (UTC+5:30)
+    ScopedTZ tz("IST-5:30");
+
+    auto tm = make_tm(2023, 1, 15, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == 330);
+}
+
+TEST_CASE("UTC Offset - Edge Case: Negative Offset Crossing Midnight", "[timezone][edge]") {
+    ScopedTZ tz(EST5EDT);
+    // Late night Dec 31st, 2023
+    auto tm = make_tm(2023, 12, 31, 23, 59);
+    REQUIRE(utc_minutes_offset(tm) == -300);
+}
+
+TEST_CASE("UTC Offset - Edge Case: Leap Year", "[timezone][edge]") {
+    ScopedTZ tz(EST5EDT);
+    // Feb 29, 2024 (Leap Day) - Winter
+    auto tm = make_tm(2024, 2, 29, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == -300);
+}
+
+TEST_CASE("UTC Offset - Edge Case: Invalid Date (Pre-Epoch)", "[timezone][edge]") {
+#ifdef _WIN32
+    // Windows mktime returns -1 for dates before 1970.
+    // We expect the function to safely return 0 (fallback).
+    auto tm = make_tm(1960, 1, 1, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == 0);
+#else
+    // Unix mktime handles pre-1970 dates correctly.
+    // We expect the actual historical offset (EST was UTC-5 in 1960).
+    ScopedTZ tz(EST5EDT);
+    auto tm = make_tm(1960, 1, 1, 12, 0);
+    REQUIRE(utc_minutes_offset(tm) == -300);
+#endif
+}
+
+#endif  // !SPDLOG_NO_TZ_OFFSET
+