fmtlib/fmt 12.2.0

on GitHub

Added a C11 API that brings fast, type-safe formatting to C. The new fmt-c library and fmt/fmt-c.h header use _Generic to dispatch on argument types and outperform printf/sprintf. For example:

#include <fmt/fmt-c.h>

fmt_print(stdout, "The answer is {}.\n", 42);

(#4663, #4671, #4696, #4693, #4694, #4712, #4789). Thanks @soumik15630m, @Ferdi265 and @localspook.

Added a separate fmt::fmt-module CMake target for C++20 modules and a CI workflow that exercises module-based builds (#4684, #4685, #4707, #4708, #4702, #4709). Thanks @MathewBensonCode.

Enabled the full Dragonbox lookup cache by default for floating-point formatting unless optimizing for binary size (__OPTIMIZE_SIZE__), giving a ~10–25% speedup. Thanks Matthias Kretz for the suggestion. Average time per double on Apple M1 Pro (clang 17, random digits, smaller is better) measured with dtoa-benchmark:

Improved integer formatting performance by ~3% (#4630). Thanks @user202729.

Optimized formatting into back-insert iterators by using bulk container append/insert methods (e.g. on std::vector<char> and custom string types) (#4679). Thanks @user202729.

Reduced binary size of debug builds (~200k to ~85k in the bloat test) and improved compile speed when consteval is unavailable.

Made path formatting lossless, preserving ill-formed UTF-16 sequences when converting std::filesystem::path to a narrow string.

Added support for formatting std::unexpected (#4675). Thanks @17steen.

Added overloads of fmt::println that take a fmt::text_style (#4782). Thanks @ahoarau.

Added support for positional arguments as width and precision specifiers in fmt::printf (#4643). Thanks @KareemOtoum.

Made FMT_STRING a no-op when FMT_USE_CONSTEVAL is enabled, since the consteval format-string constructor already provides compile-time validation (#4611, #4612). Thanks @friedkeenan.

Promoted fmt::detail::named_arg to the public API as fmt::named_arg and deprecated the detail alias (#4683, #4687). Thanks @TPPPP72.

Moved the std::byte formatter from fmt/format.h to fmt/std.h.

Provided a default definition for fmt::is_contiguous (#4731, #4770). Thanks @user202729 and @phprus.

Added the FMT_USE_FLOCKFILE macro to disable the use of flockfile (#4646, #4666). Thanks @mvastola.

Added include_guard(GLOBAL) so that {fmt} can be used in multiple submodules of the same project (#4672). Thanks @torsten48.

Improved constexpr support (#4659, #4591). Thanks @elbeno and @17steen.

Deprecated the implicit conversion from fmt::format_string and fmt::basic_fstring to string_view to align with std::format_string; use format_string::get() instead.

Opted out std::complex from tuple formatting so that the dedicated std::complex formatter is always used.

Removed the fmt::say function.

Deprecated the std::initializer_list overload of fmt::join and the array overload of fmt::vformat_to.

Made the <fmt/core.h> header equivalent to <fmt/base.h> by default. Code that relied on <fmt/core.h> pulling in <fmt/format.h> must now either include <fmt/format.h> directly or define FMT_DEPRECATED_HEAVY_CORE to opt back in.

Improved wchar_t support: fmt::join now accepts wchar_t and other non-char separators, and fmt::format_to_n now works with fmt::runtime on wchar_t (#4686, #4714, #4715). Thanks @Yancey2023 and @sunmy2019.

Fixed formatting of std::tm with a null tm_zone (#4790). Thanks @Carmel0.

Fixed compile-time formatting in fmt/ranges.h, fmt/style.h and fmt/std.h (#4759). Thanks @j4niwzis.

Fixed an ambiguity between formatter<std::optional<T>> in fmt/std.h and fmt/ranges.h on C++26 (P3168R2) (#4761). Thanks @phprus.

Fixed a GCC PCH breakage triggered by a scoped #pragma GCC optimize.

Fixed a TSAN false positive in the locale handling code (#4755).

Fixed compile-time format string checks truncating string literals at an embedded null byte (#4732). Thanks @user202729.

Fixed out-of-bounds reads in printf formatting (#4741, #4742, #4800). Thanks @Algunenano and @aizu-m.

Fixed the return type of the f(un)lockfile wrappers on Windows (#4739). Thanks @mvastola.

Worked around a CUDA issue when handling UTF-32 literals (#4719). Thanks @Cazadorro.

Fixed missing named-argument validation for compiled format strings (#4638). Thanks @jaeheonshim.

Fixed fmt::format_to_n in <fmt/compile.h> failing to compile when <iterator> is not transitively included (#4615).

Fixed handling of pointers in format string compilation with FMT_BUILTIN_TYPES=0.

Stopped assuming nul termination of the format string in fmt::printf. Thanks @ZUENS2020 for reporting.

Fixed a build error when locale support is disabled (#4627). Thanks @marcel-behlau-elfin.

Fixed a fallback range formatter for types with a container_type member (#4123, #4660). Thanks @soumik15630m.

Fixed C++20 concept detection (#4653). Thanks @tearfur.

Fixed a clang compilation failure (#4718). Thanks @mccakit.

Fixed various MSVC warnings, including C4305 and conversion warnings on x86 (#4668, #4594). Thanks @kanren3 and @blizzard4591.

Updated the Android Gradle Plugin to 9.x (#4651, #4658). Thanks @soumik15630m.

Made various code, build and test improvements (#4625, #4639, #4644, #4656, #4680, #4681, #4704, #4710, #4713, #4729, #4751, #4758, #4799). Thanks @ZephyrLykos, @togunchan, @KaganCanSit, @berndpetrovitsch, @Skylion007, @st0rmbtw, @localspook and @EXtremeExploit.

Improved documentation, including a rewrite of the format string syntax, better handling of doxygen tags, documenting output_file, fixing CSS so that whitespace is displayed properly, and various smaller fixes (#4622, #4626, #4631, #4667, #4616, #4748). Thanks @heavywatal, @ZephyrLykos, @user202729, @ssszcmawo, @bigmoonbit and @Powerbyte7.

Added building of release artifacts and SLSA provenance in CI, added a CodeQL workflow, and added the security policy in .github/SECURITY.md.