C++ Format changelog

A modern formatting library

All Versions

Latest Version

12.1.0

Avg Release Cycle

84 days

Latest Release

225 days ago

Changelog History

Page 1

v12.1.0 Changes
October 29, 2025
- ⚡️ Optimized buffer::append, resulting in up to ~16% improvement on spdlog benchmarks (#4541). Thanks @fyrsta7.
- Worked around an ABI incompatibility in std::locale_ref between clang and gcc (#4573).
- Made std::variant and std::expected formatters work with format_as (#4574, #4575). Thanks @phprus.
- Made fmt::join<string_view> work with C++ modules (#4379, #4577). Thanks @Arghnews.
- Exported fmt::is_compiled_string and operator""_cf from the module (#4544). Thanks @CrackedMatter.
- 🛠 Fixed a compatibility issue with C++ modules in clang (#4548). Thanks @tsarn.
- ➕ Added support for cv-qualified types to the std::optional formatter (#4561, #4562). Thanks @OleksandrKvl.
- ➕ Added demangling support (used in exception and std::type_info formatters) for libc++ and clang-cl (#4542, #4560, #4568, #4571). Thanks @FatihBAKIR and @rohitsutreja.
- 🆓 Switched to global malloc/free to enable allocator customization (#4569, #4570). Thanks @rohitsutreja.
- 👉 Made the FMT_USE_CONSTEVAL macro configurable by users (#4546). Thanks @SnapperTT.
- 🛠 Fixed compilation with locales disabled in the header-only mode (#4550).
- 🛠 Fixed compilation with clang 21 and -std=c++20 (#4552).
- 🛠 Fixed a dynamic linking issue with clang-cl (#4576, #4584). Thanks @FatihBAKIR.
- 🛠 Fixed a warning suppression leakage on gcc (#4588). Thanks @ZedThree.
- Made more internal color APIs constexpr (#4581). Thanks @ishani.
- 🛠 Fixed compatibility with clang as a host compiler for NVCC (#4564). Thanks @valgur.
- 🛠 Fixed various warnings and lint issues (#4565, #4572, #4557). Thanks @LiangHuDream and @teruyamato0731.
- 👌 Improved documentation (#4549, #4551, #4566, #4567, #4578,). Thanks @teruyamato0731, @petersteneteg and @zimmerman-dev.
v12.0.0 Changes
September 17, 2025
- ⚡️ Optimized the default floating point formatting (#3675, #4516). In particular, formatting a double with format string compilation into a stack allocated buffer is more than 60% faster in version 12.0 compared to 11.2 according to dtoa-benchmark:
- ➕ Added constexpr support to fmt::format. For example:
- Added FMT_STATIC_FORMAT that allows formatting into a string of the exact required size at compile time.
- 👌 Improved C++20 module support (#4451, #4459, #4476, #4488, #4491, #4495). Thanks @arBmind, @tkhyn, @Mishura4, @anonymouspc and @autoantwort.
- Switched to using estimated display width in precision. For example:
- 🛠 Fix interaction between debug presentation, precision, and width for strings (#4478). Thanks @localspook.
- Implemented allocator propagation on basic_memory_buffer move (#4487, #4490). Thanks @toprakmurat.
- Fixed an ambiguity between std::reference_wrapper<T> and format_as formatters (#4424, #4434). Thanks @jeremy-rifkin.
- ✂ Removed the following deprecated APIs:
- 🗄 Deprecated wide overloads of fmt::fprintf and fmt::sprintf.
- 👌 Improved diagnostics for the incorrect usage of fmt::ptr (#4453). Thanks @TobiSchluter.
- Made handling of ANSI escape sequences more efficient (#4511, #4528). Thanks @localspook and @Anas-Hamdane.
- 🛠 Fixed a buffer overflow on all emphasis flags set (#4498). Thanks @dominicpoeschko.
- 🛠 Fixed an integer overflow for precision close to the max int value.
- 🛠 Fixed compatibility with WASI (#4496, #4497). Thanks @whitequark.
- Fixed back_insert_iterator detection, preventing a fallback on slower path that handles arbitrary iterators (#4454).
- 🛠 Fixed handling of invalid glibc FILE buffers (#4469).
- ➕ Added wchar_t support to the std::byte formatter (#4479, #4480). Thanks @phprus.
- 🏁 Changed component prefix from fmt- to fmt_ for compatibility with NSIS/CPack on Windows, e.g. fmt-doc changed to fmt_doc (#4441, #4442). Thanks @n-stein.
- Added the FMT_CUSTOM_ASSERT_FAIL macro to simplify providing a custom fmt::assert_fail implementation (#4505). Thanks @HazardyKnusperkeks.
- Switched to FMT_THROW on reporting format errors so that it can be overriden by users when exceptions are disabled (#4521). Thanks @HazardyKnusperkeks.
- 👌 Improved master project detection and disabled install targets when using {fmt} as a subproject by default (#4536). Thanks @crueter.
- Made various code improvements (#4445, #4448, #4473, #4522). Thanks @localspook, @tchaikov and @way4sahil.
- ➕ Added Conan instructions to the docs (#4537). Thanks @uilianries.
- ✂ Removed Bazel files to avoid issues with downstream packaging (#4530). Thanks @mering.
- ➕ Added more entries for generated files to .gitignore (#4355, #4512). Thanks @dinomight and @localspook.
- 🛠 Fixed various warnings and compilation issues (#4447, #4470, #4474, #4477, #4471, #4483, #4515, #4533, #4534). Thanks @dodomorandi, @localspook, @remyjette, @Tomek-Stolarczyk, @Mishura4, @mattiasljungstrom and @FatihBAKIR.
v11.2.0 Changes
May 03, 2025
- ➕ Added the s specifier for std::error_code. It allows formatting an error message as a string. For example:
- 🛠 Fixed formatting of std::chrono::local_time and tm (#3815, #4350). For example (godbolt):
- ➕ Added diagnostics for cases when timezone information is not available. For example:
- 🗄 Deprecated fmt::localtime in favor of std::localtime.
- 🛠 Fixed compilation with GCC 15 and C++20 modules enabled (#4347). Thanks @tkhyn.
- 🛠 Fixed handling of named arguments in format specs (#4360, #4361). Thanks @dinomight.
- ➕ Added error reporting for duplicate named arguments (#4367). Thanks @dinomight.
- Fixed formatting of long with FMT_BUILTIN_TYPES=0 (#4375, #4394).
- 💅 Optimized text_style using bit packing (#4363). Thanks @localspook.
- ➕ Added support for incomplete types (#3180, #4383). Thanks @localspook.
- 🛠 Fixed a flush issue in fmt::print when using libstdc++ (#4398).
- Fixed fmt::println usage with FMT_ENFORCE_COMPILE_STRING and legacy compile-time checks (#4407). Thanks @madmaxoft.
- ✂ Removed legacy header fmt/core.h from docs (#4421, #4422). Thanks @krzysztofkortas.
- Worked around limitations of __builtin_strlen during constant evaluation (#4423, #4429). Thanks @brevzin.
- Worked around a bug in MSVC v141 (#4412, #4413). Thanks @hirohira9119.
- ✂ Removed the fmt_detail namespace (#4324).
- Removed specializations of std::is_floating_point in tests (#4417).
- Fixed a CMake error when setting CMAKE_MODULE_PATH in the pedantic mode (#4426). Thanks @rlalik.
- ⚡️ Updated the Bazel config (#4400). Thanks @Vertexwahn.
v11.1.4 Changes
February 26, 2025
- 🛠 Fixed ABI compatibility with earlier 11.x versions on Windows (#4359).
- 👌 Improved the logic of switching between fixed and exponential format for float (#3649).
- Moved is_compiled_string to the public API (#4342). Thanks @SwooshyCueb.
- Simplified implementation of operator""_cf (#4349). Thanks @localspook.
- Fixed __builtin_strlen detection (#4329). Thanks @localspook.
- 🛠 Fixed handling of BMI paths with the Ninja generator (#4344). Thanks @tkhyn.
- 🛠 Fixed gcc 8.3 compile errors (#4331, #4336). Thanks @sergiud.
- 🛠 Fixed a bogus MSVC warning (#4356). Thanks @dinomight.
v11.1.3 Changes
January 26, 2025
- 🛠 Fixed compilation on GCC 9.4 (#4313).
- Worked around an internal compiler error when using C++20 modules with GCC 14.2 and earlier (#4295).
- Worked around a bug in GCC 6 (#4318).
- 🛠 Fixed an issue caused by instantiating formatter<const T> (#4303, #4325). Thanks @timsong-cpp.
- 🛠 Fixed formatting into std::ostreambuf_iterator when using format string compilation (#4309, #4312). Thanks @phprus.
- ⏪ Restored a constraint on the map formatter so that it correctly reports as unformattable when the element is (#4326). Thanks @timsong-cpp.
- ⬇️ Reduced the size of format specs (#4298).
- Readded args() to fmt::format_context (#4307, #4310). Thanks @Erroneous1.
- 🛠 Fixed a bogus MSVC warning (#4314, #4322). Thanks @ZehMatt.
- 🛠 Fixed a pedantic mode error in the CMake config (#4327). Thanks @rlalik.
v11.1.2 Changes
January 12, 2025
- 🛠 Fixed ABI compatibility with earlier 11.x versions (#4292).
- ➕ Added wchar_t support to the std::bitset formatter (#4285, #4286, #4289, #4290). Thanks @phprus.
- 🛠 Prefixed CMake components with fmt- to simplify usage of {fmt} via add_subdirectory (#4283).
- ⚡️ Updated docs for meson (#4291). Thanks @trim21.
- 🛠 Fixed a compilation error in chrono on nvcc (#4297, #4301). Thanks @breyerml.
- 🛠 Fixed various warnings (#4288, #4299). Thanks @GamesTrap and @edo9300.
v11.1.1 Changes
December 27, 2024
- 🛠 Fixed ABI compatibility with earlier 11.x versions (#4278).
- 📄 Defined CMake components (core and doc) to allow docs to be installed separately (#4276). Thanks @carlsmedstad.
v11.1.0 Changes
December 25, 2024
- 👌 Improved C++20 module support (#4081, #4083, #4084, #4152, #4153, #4169, #4190, #4234, #4239). Thanks @kamrann and @Arghnews.
- ⚡️ Reduced debug (unoptimized) binary code size and the number of template instantiations when passing formatting arguments. For example, unoptimized binary code size for fmt::print("{}", 42) was reduced by ~40% on GCC and ~60% on clang (x86-64).
- ➕ Added an experimental fmt::writer API that can be used for writing to different destinations such as files or strings (#2354). For example (godbolt):
- ➕ Added width and alignment support to the formatter of std::error_code.
- Made std::expected<void, E> formattable (#4145, #4148). For example (godbolt):
- Made fmt::is_formattable<void> SFINAE-friendly (#4147).
- ➕ Added support for _BitInt formatting when using clang (#4007, #4072, #4140, #4173, #4176). For example (godbolt):
- ➕ Added the n specifier for tuples and pairs (#4107). Thanks @someonewithpc.
- ➕ Added support for tuple-like types to fmt::join (#4226, #4230). Thanks @phprus.
- Made more types formattable at compile time (#4127). Thanks @AnthonyVH.
- Implemented a more efficient compile-time fmt::formatted_size (#4102, #4103). Thanks @phprus.
- 🛠 Fixed compile-time formatting of some string types (#4065). Thanks @torshepherd.
- Made compiled version of fmt::format_to work with std::back_insert_iterator<std::vector<char>> (#4206, #4211). Thanks @phprus.
- ➕ Added a formatter for std::reference_wrapper (#4163, #4164). Thanks @yfeldblum and @phprus.
- ➕ Added experimental padding support (glibc strftime extension) to %m, %j and %Y (#4161). Thanks @KKhanhH.
- 👍 Made microseconds formatted as us instead of µs if the Unicode support is disabled (#4088).
- 🛠 Fixed an unreleased regression in transcoding of surrogate pairs (#4094, #4095). Thanks @phprus.
- Made fmt::appender satisfy std::output_iterator concept (#4092, #4093). Thanks @phprus.
- Made std::iterator_traits<fmt::appender> standard-conforming (#4185). Thanks @CaseyCarter.
- Made it easier to reuse fmt::formatter<std::string_view> for types with an implicit conversion to std::string_view (#4036, #4055). Thanks @Arghnews.
- Made it possible to disable <filesystem> use via FMT_CPP_LIB_FILESYSTEM for compatibility with some video game console SDKs, e.g. Nintendo Switch SDK (#4257, #4258, #4259). Thanks @W4RH4WK and @phprus.
- 🛠 Fixed compatibility with platforms that use 80-bit long double (#4245, #4246). Thanks @jsirpoma.
- ➕ Added support for UTF-32 code units greater than 0xFFFF in fill (#4201).
- 🛠 Fixed handling of legacy encodings on Windows with GCC (#4162).
- Made fmt::to_string take fmt::basic_memory_buffer by const reference (#4261, #4262). Thanks @sascha-devel.
- Added fmt::dynamic_format_arg_store::size (#4270). Thanks @hannes-harnisch.
- Removed the ability to control locale usage via an undocumented FMT_STATIC_THOUSANDS_SEPARATOR in favor of FMT_USE_LOCALE.
- Renamed FMT_EXCEPTIONS to FMT_USE_EXCEPTIONS for consistency with other similar macros.
- 👌 Improved include directory ordering to reduce the chance of including incorrect headers when using multiple versions of {fmt} (#4116). Thanks @cdzhan.
- Made it possible to compile a subset of {fmt} without the C++ runtime.
- 👌 Improved documentation and README (#4066, #4117, #4203, #4235). Thanks @zyctree and @nikola-sh.
- 👌 Improved the documentation generator (#4110, #4115). Thanks @rturrado.
- 👌 Improved CI (#4155, #4151). Thanks @phprus.
- 🛠 Fixed various warnings and compilation issues (#2708, #4091, #4109, #4113, #4125, #4129, #4130, #4131, #4132, #4133, #4144, #4150, #4158, #4159, #4160, #4170, #4177, #4187, #4188, #4194, #4200, #4205, #4207, #4208, #4210, #4220, #4231, #4232, #4233, #4236, #4267, #4271). Thanks @torsten48, @Arghnews, @tinfoilboy, @aminya, @Ottani, @zeroomega, @c4v4, @kongy, @vinayyadav3016, @sergio-nsk, @phprus and @YexuanXiao.
v11.0.2 Changes
July 20, 2024
- 🛠 Fixed compatibility with non-POSIX systems (#4054, #4060).
- Fixed performance regressions when using std::back_insert_iterator with fmt::format_to (#4070).
- 🛠 Fixed handling of std::generator and move-only iterators (#4053, #4057). Thanks @Arghnews.
- 📜 Made formatter<std::string_view>::parse work with types convertible to std::string_view (#4036, #4055). Thanks @Arghnews.
- Made volatile void* formattable (#4049, #4056). Thanks @Arghnews.
- Made Glib::ustring not be confused with std::string (#4052).
- Made fmt::context iterator compatible with STL algorithms that rely on iterator category (#4079).
v11.0.1 Changes
July 05, 2024
- 🛠 Fixed version number in the inline namespace (#4047).
- 🛠 Fixed disabling Unicode support via CMake (#4051).
- Fixed deprecated visit_format_arg (#4043). Thanks @nebkat.
- 🛠 Fixed handling of a sign and improved the std::complex formater (#4034, #4050). Thanks @tesch1 and @phprus.
- 🛠 Fixed ADL issues in fmt::printf when using C++20 (#4042). Thanks @toge.
- ✂ Removed a redundant check in the formatter for std::expected (#4040). Thanks @phprus.