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9.0.0 - TBD

8.1.1 - 2022-01-06

8.1.0 - 2022-01-02

8.0.1 - 2021-07-02

8.0.0 - 2021-06-21

  • Enabled compile-time format string checks by default. For example (godbolt):

    #include <fmt/core.h>

int main() {
  fmt::print("{:d}", "I am not a number");
}

    gives a compile-time error on compilers with C++20 consteval support (gcc 10+, clang 11+) because d is not a valid format specifier for a string.

    To pass a runtime string wrap it in fmt::runtime:

    fmt::print(fmt::runtime("{:d}"), "I am not a number");

  • Added compile-time formatting (#2019, #2044, #2056, #2072, #2075, #2078, #2129, #2326). For example (godbolt):

    #include <fmt/compile.h>

consteval auto compile_time_itoa(int value) -> std::array<char, 10> {
  auto result = std::array<char, 10>();
  fmt::format_to(result.data(), FMT_COMPILE("{}"), value);
  return result;
}

constexpr auto answer = compile_time_itoa(42);

    Most of the formatting functionality is available at compile time with a notable exception of floating-point numbers and pointers. Thanks @alexezeder (Alexey Ochapov).

  • Optimized handling of format specifiers during format string compilation. For example, hexadecimal formatting ("{:x}") is now 3-7x faster than before when using format_to with format string compilation and a stack-allocated buffer (#1944).

    Before (7.1.3):

    ----------------------------------------------------------------------------
Benchmark                                  Time             CPU   Iterations
----------------------------------------------------------------------------
FMTCompileOld/0                         15.5 ns         15.5 ns     43302898
FMTCompileOld/42                        16.6 ns         16.6 ns     43278267
FMTCompileOld/273123                    18.7 ns         18.6 ns     37035861
FMTCompileOld/9223372036854775807       19.4 ns         19.4 ns     35243000
----------------------------------------------------------------------------

    After (8.x):

    ----------------------------------------------------------------------------
Benchmark                                  Time             CPU   Iterations
----------------------------------------------------------------------------
FMTCompileNew/0                         1.99 ns         1.99 ns    360523686
FMTCompileNew/42                        2.33 ns         2.33 ns    279865664
FMTCompileNew/273123                    3.72 ns         3.71 ns    190230315
FMTCompileNew/9223372036854775807       5.28 ns         5.26 ns    130711631
----------------------------------------------------------------------------

    It is even faster than std::to_chars from libc++ compiled with clang on macOS:

    ----------------------------------------------------------------------------
Benchmark                                  Time             CPU   Iterations
----------------------------------------------------------------------------
ToChars/0                               4.42 ns         4.41 ns    160196630
ToChars/42                              5.00 ns         4.98 ns    140735201
ToChars/273123                          7.26 ns         7.24 ns     95784130
ToChars/9223372036854775807             8.77 ns         8.75 ns     75872534
----------------------------------------------------------------------------

    In other cases, especially involving std::string construction, the speed up is usually lower because handling format specifiers takes a smaller fraction of the total time.

  • Added the _cf user-defined literal to represent a compiled format string. It can be used instead of the FMT_COMPILE macro (#2043, #2242):

    #include <fmt/compile.h>

using namespace fmt::literals;
auto s = fmt::format(FMT_COMPILE("{}"), 42); // 🙁 not modern
auto s = fmt::format("{}"_cf, 42);           // 🙂 modern as hell

    It requires compiler support for class types in non-type template parameters (a C++20 feature) which is available in GCC 9.3+. Thanks @alexezeder (Alexey Ochapov).

  • Format string compilation now requires format functions of formatter specializations for user-defined types to be const:

    template <> struct fmt::formatter<my_type>: formatter<string_view> {
  template <typename FormatContext>
  auto format(my_type obj, FormatContext& ctx) const {  // Note const here.
    // ...
  }
};

  • Added UDL-based named argument support to format string compilation (#2243, #2281). For example:

    #include <fmt/compile.h>

using namespace fmt::literals;
auto s = fmt::format(FMT_COMPILE("{answer}"), "answer"_a = 42);

    Here the argument named "answer" is resolved at compile time with no runtime overhead. Thanks @alexezeder (Alexey Ochapov).

  • Added format string compilation support to fmt::print (#2280, #2304). Thanks @alexezeder (Alexey Ochapov).

  • Added initial support for compiling {fmt} as a C++20 module (#2235, #2240, #2260, #2282, #2283, #2288, #2298, #2306, #2307, #2309, #2318, #2324, #2332, #2340). Thanks @DanielaE (Daniela Engert).

  • Made symbols private by default reducing shared library size (#2301). For example there was a ~15% reported reduction on one platform. Thanks @sergiud (Sergiu Deitsch).

  • Optimized includes making the result of preprocessing fmt/format.h ~20% smaller with libstdc++/C++20 and slightly improving build times (#1998).

  • Added support of ranges with non-const begin / end (#1953). Thanks @kitegi (sarah).

  • Added support of std::byte and other formattable types to fmt::join (#1981, #2040, #2050, #2262). For example:

    #include <fmt/format.h>
#include <cstddef>
#include <vector>

int main() {
  auto bytes = std::vector{std::byte(4), std::byte(2)};
  fmt::print("{}", fmt::join(bytes, ""));
}

    prints "42".

    Thanks @kamibo (Camille Bordignon).

  • Implemented the default format for std::chrono::system_clock (#2319, #2345). For example:

    #include <fmt/chrono.h>

int main() {
  fmt::print("{}", std::chrono::system_clock::now());
}

    prints "2021-06-18 15:22:00" (the output depends on the current date and time). Thanks @sunmy2019.

  • Made more chrono specifiers locale independent by default. Use the 'L' specifier to get localized formatting. For example:

    #include <fmt/chrono.h>

int main() {
  std::locale::global(std::locale("ru_RU.UTF-8"));
  auto monday = std::chrono::weekday(1);
  fmt::print("{}\n", monday);   // prints "Mon"
  fmt::print("{:L}\n", monday); // prints "пн"
}

  • Improved locale handling in chrono formatting (#2337, #2349, #2350). Thanks @phprus (Vladislav Shchapov).

  • Deprecated fmt/locale.h moving the formatting functions that take a locale to fmt/format.h (char) and fmt/xchar (other overloads). This doesn't introduce a dependency on <locale> so there is virtually no compile time effect.

  • Deprecated an undocumented format_to overload that takes basic_memory_buffer.

  • Made parameter order in vformat_to consistent with format_to (#2327).

  • Added support for time points with arbitrary durations (#2208). For example:

    #include <fmt/chrono.h>

int main() {
  using tp = std::chrono::time_point<
    std::chrono::system_clock, std::chrono::seconds>;
  fmt::print("{:%S}", tp(std::chrono::seconds(42)));
}

    prints "42".

  • Formatting floating-point numbers no longer produces trailing zeros by default for consistency with std::format. For example:

    #include <fmt/core.h>

int main() {
  fmt::print("{0:.3}", 1.1);
}

    prints "1.1". Use the '#' specifier to keep trailing zeros.

  • Dropped a limit on the number of elements in a range and replaced {} with [] as range delimiters for consistency with Python's str.format.

  • The 'L' specifier for locale-specific numeric formatting can now be combined with presentation specifiers as in std::format. For example:

    #include <fmt/core.h>
#include <locale>

int main() {
  std::locale::global(std::locale("fr_FR.UTF-8"));
  fmt::print("{0:.2Lf}", 0.42);
}

    prints "0,42". The deprecated 'n' specifier has been removed.

  • Made the 0 specifier ignored for infinity and NaN (#2305, #2310). Thanks @Liedtke (Matthias Liedtke).

  • Made the hexfloat formatting use the right alignment by default (#2308, #2317). Thanks @Liedtke (Matthias Liedtke).

  • Removed the deprecated numeric alignment ('='). Use the '0' specifier instead.

  • Removed the deprecated fmt/posix.h header that has been replaced with fmt/os.h.

  • Removed the deprecated format_to_n_context, format_to_n_args and make_format_to_n_args. They have been replaced with format_context, format_args` and ``make_format_args respectively.

  • Moved wchar_t-specific functions and types to fmt/xchar.h. You can define FMT_DEPRECATED_INCLUDE_XCHAR to automatically include fmt/xchar.h from fmt/format.h but this will be disabled in the next major release.

  • Fixed handling of the '+' specifier in localized formatting (#2133).

  • Added support for the 's' format specifier that gives textual representation of bool (#2094, #2109). For example:

    #include <fmt/core.h>

int main() {
  fmt::print("{:s}", true);
}

    prints "true". Thanks @powercoderlol (Ivan Polyakov).

  • Made fmt::ptr work with function pointers (#2131). For example:

    #include <fmt/format.h>

int main() {
  fmt::print("My main: {}\n", fmt::ptr(main));
}

    Thanks @mikecrowe (Mike Crowe).

  • The undocumented support for specializing formatter for pointer types has been removed.

  • Fixed fmt::formatted_size with format string compilation (#2141, #2161). Thanks @alexezeder (Alexey Ochapov).

  • Fixed handling of empty format strings during format string compilation (#2042):

    auto s = fmt::format(FMT_COMPILE(""));

    Thanks @alexezeder (Alexey Ochapov).

  • Fixed handling of enums in fmt::to_string (#2036).

  • Improved width computation (#2033, #2091). For example:

    #include <fmt/core.h>

int main() {
  fmt::print("{:-<10}{}\n", "你好", "世界");
  fmt::print("{:-<10}{}\n", "hello", "world");
}

    prints

    https://user-images.githubusercontent.com/576385/119840373-cea3ca80-beb9-11eb-91e0-54266c48e181.png

    on a modern terminal.

  • The experimental fast output stream (fmt::ostream) is now truncated by default for consistency with fopen (#2018). For example:

    #include <fmt/os.h>

int main() {
  fmt::ostream out1 = fmt::output_file("guide");
  out1.print("Zaphod");
  out1.close();
  fmt::ostream out2 = fmt::output_file("guide");
  out2.print("Ford");
}

    writes "Ford" to the file "guide". To preserve the old file content if any pass fmt::file::WRONLY | fmt::file::CREATE flags to fmt::output_file.

  • Fixed moving of fmt::ostream that holds buffered data (#2197, #2198). Thanks @vtta.

  • Replaced the fmt::system_error exception with a function of the same name that constructs std::system_error (#2266).

  • Replaced the fmt::windows_error exception with a function of the same name that constructs std::system_error with the category returned by fmt::system_category() (#2274, #2275). The latter is similar to std::sytem_category but correctly handles UTF-8. Thanks @phprus (Vladislav Shchapov).

  • Replaced fmt::error_code with std::error_code and made it formattable (#2269, #2270, #2273). Thanks @phprus (Vladislav Shchapov).

  • Added speech synthesis support (#2206).

  • Made format_to work with a memory buffer that has a custom allocator (#2300). Thanks @voxmea.

  • Added Allocator::max_size support to basic_memory_buffer. (#1960). Thanks @phprus (Vladislav Shchapov).

  • Added wide string support to fmt::join (#2236). Thanks @crbrz.

  • Made iterators passed to formatter specializations via a format context satisfy C++20 std::output_iterator requirements (#2156, #2158, #2195, #2204). Thanks @randomnetcat (Jason Cobb).

  • Optimized the printf implementation (#1982, #1984, #2016, #2164). Thanks @rimathia and @moiwi.

  • Improved detection of constexpr char_traits (#2246, #2257). Thanks @phprus (Vladislav Shchapov).

  • Fixed writing to stdout when it is redirected to NUL on Windows (#2080).

  • Fixed exception propagation from iterators (#2097).

  • Improved strftime error handling (#2238, #2244). Thanks @yumeyao.

  • Stopped using deprecated GCC UDL template extension.

  • Added fmt/args.h to the install target (#2096).

  • Error messages are now passed to assert when exceptions are disabled (#2145). Thanks @NobodyXu (Jiahao XU).

  • Added the FMT_MASTER_PROJECT CMake option to control build and install targets when {fmt} is included via add_subdirectory (#2098, #2100). Thanks @randomizedthinking.

  • Improved build configuration (#2026, #2122). Thanks @luncliff (Park DongHa) and @ibaned (Dan Ibanez).

  • Fixed various warnings and compilation issues (#1947, #1959, #1963, #1965, #1966, #1974, #1975, #1990, #2000, #2001, #2002, #2004, #2006, #2009, #2010, #2038, #2039, #2047, #2053, #2059, #2065, #2067, #2068, #2073, #2103, #2105, #2106, #2107, #2116, #2117, #2118, #2119, #2127, #2128, #2140, #2142, #2143, #2144, #2147, #2148, #2149, #2152, #2160, #2170, #2175, #2176, #2177, #2178, #2179, #2180, #2181, #2183, #2184, #2185, #2186, #2187, #2190, #2192, #2194, #2205, #2210, #2211, #2215, #2216, #2218, #2220, #2228, #2229, #2230, #2233, #2239, #2248, #2252, #2253, #2255, #2261, #2278, #2284, #2287, #2289, #2290, #2293, #2295, #2296, #2297, #2311, #2313, #2315, #2320, #2321, #2323, #2328, #2329, #2333, #2338, #2341). Thanks @darklukee, @fagg (Ashton Fagg), @killerbot242 (Lieven de Cock), @jgopel (Jonathan Gopel), @yeswalrus (Walter Gray), @Finkman, @HazardyKnusperkeks (Björn Schäpers), @dkavolis (Daumantas Kavolis), @concatime (Issam Maghni), @chronoxor (Ivan Shynkarenka), @summivox (Yin Zhong), @yNeo, @Apache-HB (Elliot), @alexezeder (Alexey Ochapov), @toojays (John Steele Scott), @Brainy0207, @vadz (VZ), @imsherlock (Ryan Sherlock), @phprus (Vladislav Shchapov), @white238 (Chris White), @yafshar (Yaser Afshar), @BillyDonahue (Billy Donahue), @jstaahl, @denchat, @DanielaE (Daniela Engert), @ilyakurdyukov (Ilya Kurdyukov), @ilmai, @JessyDL (Jessy De Lannoit), @sergiud (Sergiu Deitsch), @mwinterb, @sven-herrmann, @jmelas (John Melas), @twoixter (Jose Miguel Pérez), @crbrz, @upsj (Tobias Ribizel).

  • Improved documentation (#1986, #2051, #2057, #2081, #2084, #2312). Thanks @imba-tjd (谭九鼎), @0x416c69 (AlιAѕѕaѕѕιN), @mordante.

  • Continuous integration and test improvements (#1969, #1991, #2020, #2110, #2114, #2196, #2217, #2247, #2256, #2336, #2346). Thanks @jgopel (Jonathan Gopel), @alexezeder (Alexey Ochapov) and @DanielaE (Daniela Engert).

7.1.3 - 2020-11-24

  • Fixed handling of buffer boundaries in format_to_n (#1996, #2029).
  • Fixed linkage errors when linking with a shared library (#2011).
  • Reintroduced ostream support to range formatters (#2014).
  • Worked around an issue with mixing std versions in gcc (#2017).

7.1.2 - 2020-11-04

  • Fixed floating point formatting with large precision (#1976).

7.1.1 - 2020-11-01

  • Fixed ABI compatibility with 7.0.x (#1961).
  • Added the FMT_ARM_ABI_COMPATIBILITY macro to work around ABI incompatibility between GCC and Clang on ARM (#1919).
  • Worked around a SFINAE bug in GCC 8 (#1957).
  • Fixed linkage errors when building with GCC's LTO (#1955).
  • Fixed a compilation error when building without __builtin_clz or equivalent (#1968). Thanks @tohammer (Tobias Hammer).
  • Fixed a sign conversion warning (#1964). Thanks @OptoCloud.

7.1.0 - 2020-10-25

  • Switched from Grisu3 to Dragonbox for the default floating-point formatting which gives the shortest decimal representation with round-trip guarantee and correct rounding (#1882, #1887, #1894). This makes {fmt} up to 20-30x faster than common implementations of std::ostringstream and sprintf on dtoa-benchmark and faster than double-conversion and Ryū:

    https://user-images.githubusercontent.com/576385/95684665-11719600-0ba8-11eb-8e5b-972ff4e49428.png

    It is possible to get even better performance at the cost of larger binary size by compiling with the FMT_USE_FULL_CACHE_DRAGONBOX macro set to 1.

    Thanks @jk-jeon (Junekey Jeon).

  • Added an experimental unsynchronized file output API which, together with format string compilation, can give 5-9 times speed up compared to fprintf on common platforms (godbolt):

    #include <fmt/os.h>

int main() {
  auto f = fmt::output_file("guide");
  f.print("The answer is {}.", 42);
}

  • Added a formatter for std::chrono::time_point<system_clock> (#1819, #1837). For example (godbolt):

    #include <fmt/chrono.h>

int main() {
  auto now = std::chrono::system_clock::now();
  fmt::print("The time is {:%H:%M:%S}.\n", now);
}

    Thanks @adamburgess (Adam Burgess).

  • Added support for ranges with non-const begin/end to fmt::join (#1784, #1786). For example (godbolt):

    #include <fmt/ranges.h>
#include <range/v3/view/filter.hpp>

int main() {
  using std::literals::string_literals::operator""s;
  auto strs = std::array{"a"s, "bb"s, "ccc"s};
  auto range = strs | ranges::views::filter(
    [] (const std::string &x) { return x.size() != 2; }
  );
  fmt::print("{}\n", fmt::join(range, ""));
}

    prints "accc".

    Thanks @tonyelewis (Tony E Lewis).

  • Added a memory_buffer::append overload that takes a range (#1806). Thanks @BRevzin (Barry Revzin).

  • Improved handling of single code units in FMT_COMPILE. For example:

    #include <fmt/compile.h>

char* f(char* buf) {
  return fmt::format_to(buf, FMT_COMPILE("x{}"), 42);
}

    compiles to just (godbolt):

    _Z1fPc:
  movb $120, (%rdi)
  xorl %edx, %edx
  cmpl $42, _ZN3fmt2v76detail10basic_dataIvE23zero_or_powers_of_10_32E+8(%rip)
  movl $3, %eax
  seta %dl
  subl %edx, %eax
  movzwl _ZN3fmt2v76detail10basic_dataIvE6digitsE+84(%rip), %edx
  cltq
  addq %rdi, %rax
  movw %dx, -2(%rax)
  ret

    Here a single mov instruction writes 'x' ($120) to the output buffer.

  • Added dynamic width support to format string compilation (#1809).

  • Improved error reporting for unformattable types: now you'll get the type name directly in the error message instead of the note:

    #include <fmt/core.h>

struct how_about_no {};

int main() {
  fmt::print("{}", how_about_no());
}

    Error (godbolt):

    fmt/core.h:1438:3: error: static_assert failed due to requirement 'fmt::v7::formattable<how_about_no>()' "Cannot format an argument. To make type T formattable provide a formatter<T> specialization: https://fmt.dev/latest/api.html#udt" ...

  • Added the make_args_checked function template that allows you to write formatting functions with compile-time format string checks and avoid binary code bloat (godbolt):

    void vlog(const char* file, int line, fmt::string_view format,
          fmt::format_args args) {
  fmt::print("{}: {}: ", file, line);
  fmt::vprint(format, args);
}

template <typename S, typename... Args>
void log(const char* file, int line, const S& format, Args&&... args) {
  vlog(file, line, format,
      fmt::make_args_checked<Args...>(format, args...));
}

#define MY_LOG(format, ...) \
  log(__FILE__, __LINE__, FMT_STRING(format), __VA_ARGS__)

MY_LOG("invalid squishiness: {}", 42);

  • Replaced snprintf fallback with a faster internal IEEE 754 float and double formatter for arbitrary precision. For example (godbolt):

    #include <fmt/core.h>

int main() {
  fmt::print("{:.500}\n", 4.9406564584124654E-324);
}

    prints

    4.9406564584124654417656879286822137236505980261432476442558568250067550727020875186529983636163599237979656469544571773092665671035593979639877479601078187812630071319031140452784581716784898210368871863605699873072305000638740915356498438731247339727316961514003171538539807412623856559117102665855668676818703956031062493194527159149245532930545654440112748012970999954193198940908041656332452475714786901472678015935523861155013480352649347201937902681071074917033322268447533357208324319360923829e-324.

  • Made format_to_n and formatted_size part of the core API (godbolt):

    #include <fmt/core.h>

int main() {
  char buffer[10];
  auto result = fmt::format_to_n(buffer, sizeof(buffer), "{}", 42);
}

  • Added fmt::format_to_n overload with format string compilation (#1764, #1767, #1869). For example (godbolt):

    #include <fmt/compile.h>

int main() {
  char buffer[8];
  fmt::format_to_n(buffer, sizeof(buffer), FMT_COMPILE("{}"), 42);
}

    Thanks @Kurkin (Dmitry Kurkin), @alexezeder (Alexey Ochapov).

  • Added fmt::format_to overload that take text_style (#1593, #1842, #1843). For example (godbolt):

    #include <fmt/color.h>

int main() {
  std::string out;
  fmt::format_to(std::back_inserter(out),
                 fmt::emphasis::bold | fg(fmt::color::red),
                 "The answer is {}.", 42);
}

    Thanks @Naios (Denis Blank).

  • Made the '#' specifier emit trailing zeros in addition to the decimal point (#1797). For example (godbolt):

    #include <fmt/core.h>

int main() {
  fmt::print("{:#.2g}", 0.5);
}

    prints 0.50.

  • Changed the default floating point format to not include .0 for consistency with std::format and std::to_chars (#1893, #1943). It is possible to get the decimal point and trailing zero with the # specifier.

  • Fixed an issue with floating-point formatting that could result in addition of a non-significant trailing zero in rare cases e.g. 1.00e-34 instead of 1.0e-34 (#1873, #1917).

  • Made fmt::to_string fallback on ostream insertion operator if the formatter specialization is not provided (#1815, #1829). Thanks @alexezeder (Alexey Ochapov).

  • Added support for the append mode to the experimental file API and improved fcntl.h detection. (#1847, #1848). Thanks @t-wiser.

  • Fixed handling of types that have both an implicit conversion operator and an overloaded ostream insertion operator (#1766).

  • Fixed a slicing issue in an internal iterator type (#1822). Thanks @BRevzin (Barry Revzin).

  • Fixed an issue in locale-specific integer formatting (#1927).

  • Fixed handling of exotic code unit types (#1870, #1932).

  • Improved FMT_ALWAYS_INLINE (#1878). Thanks @jk-jeon (Junekey Jeon).

  • Removed dependency on windows.h (#1900). Thanks @bernd5 (Bernd Baumanns).

  • Optimized counting of decimal digits on MSVC (#1890). Thanks @mwinterb.

  • Improved documentation (#1772, #1775, #1792, #1838, #1888, #1918, #1939). Thanks @leolchat (Léonard Gérard), @pepsiman (Malcolm Parsons), @Klaim (Joël Lamotte), @ravijanjam (Ravi J), @francesco-st, @udnaan (Adnan).

  • Added the FMT_REDUCE_INT_INSTANTIATIONS CMake option that reduces the binary code size at the cost of some integer formatting performance. This can be useful for extremely memory-constrained embedded systems (#1778, #1781). Thanks @kammce (Khalil Estell).

  • Added the FMT_USE_INLINE_NAMESPACES macro to control usage of inline namespaces (#1945). Thanks @darklukee.

  • Improved build configuration (#1760, #1770, #1779, #1783, #1823). Thanks @dvetutnev (Dmitriy Vetutnev), @xvitaly (Vitaly Zaitsev), @tambry (Raul Tambre), @medithe, @martinwuehrer (Martin Wührer).

  • Fixed various warnings and compilation issues (#1790, #1802, #1808, #1810, #1811, #1812, #1814, #1816, #1817, #1818, #1825, #1836, #1855, #1856, #1860, #1877, #1879, #1880, #1896, #1897, #1898, #1904, #1908, #1911, #1912, #1928, #1929, #1935, #1937, #1942, #1949). Thanks @TheQwertiest, @medithe, @martinwuehrer (Martin Wührer), @n16h7hunt3r, @Othereum (Seokjin Lee), @gsjaardema (Greg Sjaardema), @AlexanderLanin (Alexander Lanin), @gcerretani (Giovanni Cerretani), @chronoxor (Ivan Shynkarenka), @noizefloor (Jan Schwers), @akohlmey (Axel Kohlmeyer), @jk-jeon (Junekey Jeon), @rimathia, @rglarix (Riccardo Ghetta (larix)), @moiwi, @heckad (Kazantcev Andrey), @MarcDirven. @BartSiwek (Bart Siwek), @darklukee.

7.0.3 - 2020-08-06

  • Worked around broken numeric_limits for 128-bit integers (#1787).
  • Added error reporting on missing named arguments (#1796).
  • Stopped using 128-bit integers with clang-cl (#1800). Thanks @Kingcom.
  • Fixed issues in locale-specific integer formatting (#1782, #1801).

7.0.2 - 2020-07-29

  • Worked around broken numeric_limits for 128-bit integers (#1725).
  • Fixed compatibility with CMake 3.4 (#1779).
  • Fixed handling of digit separators in locale-specific formatting (#1782).

7.0.1 - 2020-07-07

  • Updated the inline version namespace name.
  • Worked around a gcc bug in mangling of alias templates (#1753).
  • Fixed a linkage error on Windows (#1757). Thanks @Kurkin (Dmitry Kurkin).
  • Fixed minor issues with the documentation.

7.0.0 - 2020-07-05

  • Reduced the library size. For example, on macOS a stripped test binary statically linked with {fmt} shrank from ~368k to less than 100k.

  • Added a simpler and more efficient format string compilation API:

    #include <fmt/compile.h>

// Converts 42 into std::string using the most efficient method and no
// runtime format string processing.
std::string s = fmt::format(FMT_COMPILE("{}"), 42);

    The old fmt::compile API is now deprecated.

  • Optimized integer formatting: format_to with format string compilation and a stack-allocated buffer is now faster than to_chars on both libc++ and libstdc++.

  • Optimized handling of small format strings. For example,

    fmt::format("Result: {}: ({},{},{},{})", str1, str2, str3, str4, str5)

    is now ~40% faster (#1685).

  • Applied extern templates to improve compile times when using the core API and fmt/format.h (#1452). For example, on macOS with clang the compile time of a test translation unit dropped from 2.3s to 0.3s with -O2 and from 0.6s to 0.3s with the default settings (-O0).

    Before (-O2):

    % time c++ -c test.cc -I include -std=c++17 -O2
c++ -c test.cc -I include -std=c++17 -O2  2.22s user 0.08s system 99% cpu 2.311 total

    After (-O2):

    % time c++ -c test.cc -I include -std=c++17 -O2
c++ -c test.cc -I include -std=c++17 -O2  0.26s user 0.04s system 98% cpu 0.303 total

    Before (default):

    % time c++ -c test.cc -I include -std=c++17
c++ -c test.cc -I include -std=c++17  0.53s user 0.06s system 98% cpu 0.601 total

    After (default):

    % time c++ -c test.cc -I include -std=c++17
c++ -c test.cc -I include -std=c++17  0.24s user 0.06s system 98% cpu 0.301 total

    It is still recommended to use fmt/core.h instead of fmt/format.h but the compile time difference is now smaller. Thanks @alex3d for the suggestion.

  • Named arguments are now stored on stack (no dynamic memory allocations) and the compiled code is more compact and efficient. For example

    #include <fmt/core.h>

int main() {
  fmt::print("The answer is {answer}\n", fmt::arg("answer", 42));
}

    compiles to just (godbolt)

    .LC0:
        .string "answer"
.LC1:
        .string "The answer is {answer}\n"
main:
        sub     rsp, 56
        mov     edi, OFFSET FLAT:.LC1
        mov     esi, 23
        movabs  rdx, 4611686018427387905
        lea     rax, [rsp+32]
        lea     rcx, [rsp+16]
        mov     QWORD PTR [rsp+8], 1
        mov     QWORD PTR [rsp], rax
        mov     DWORD PTR [rsp+16], 42
        mov     QWORD PTR [rsp+32], OFFSET FLAT:.LC0
        mov     DWORD PTR [rsp+40], 0
        call    fmt::v6::vprint(fmt::v6::basic_string_view<char>,
                                fmt::v6::format_args)
        xor     eax, eax
        add     rsp, 56
        ret

    .L.str.1:
            .asciz  "answer"

  • Implemented compile-time checks for dynamic width and precision (#1614):

    #include <fmt/format.h>

int main() {
  fmt::print(FMT_STRING("{0:{1}}"), 42);
}

    now gives a compilation error because argument 1 doesn't exist:

    In file included from test.cc:1:
include/fmt/format.h:2726:27: error: constexpr variable 'invalid_format' must be
initialized by a constant expression
  FMT_CONSTEXPR_DECL bool invalid_format =
                          ^
...
include/fmt/core.h:569:26: note: in call to
'&checker(s, {}).context_->on_error(&"argument not found"[0])'
    if (id >= num_args_) on_error("argument not found");
                        ^

  • Added sentinel support to fmt::join (#1689)

    struct zstring_sentinel {};
bool operator==(const char* p, zstring_sentinel) { return *p == '\0'; }
bool operator!=(const char* p, zstring_sentinel) { return *p != '\0'; }

struct zstring {
  const char* p;
  const char* begin() const { return p; }
  zstring_sentinel end() const { return {}; }
};

auto s = fmt::format("{}", fmt::join(zstring{"hello"}, "_"));
// s == "h_e_l_l_o"

    Thanks @BRevzin (Barry Revzin).

  • Added support for named arguments, clear and reserve to dynamic_format_arg_store (#1655, #1663, #1674, #1677). Thanks @vsolontsov-ll (Vladimir Solontsov).

  • Added support for the 'c' format specifier to integral types for compatibility with std::format (#1652).

  • Replaced the 'n' format specifier with 'L' for compatibility with std::format (#1624). The 'n' specifier can be enabled via the FMT_DEPRECATED_N_SPECIFIER macro.

  • The '=' format specifier is now disabled by default for compatibility with std::format. It can be enabled via the FMT_DEPRECATED_NUMERIC_ALIGN macro.

  • Removed the following deprecated APIs:

    • FMT_STRING_ALIAS and fmt macros - replaced by FMT_STRING
    • fmt::basic_string_view::char_type - replaced by fmt::basic_string_view::value_type
    • convert_to_int
    • format_arg_store::types
    • *parse_context - replaced by *format_parse_context
    • FMT_DEPRECATED_INCLUDE_OS
    • FMT_DEPRECATED_PERCENT - incompatible with std::format
    • *writer - replaced by compiled format API

  • Renamed the internal namespace to detail (#1538). The former is still provided as an alias if the FMT_USE_INTERNAL macro is defined.

  • Improved compatibility between fmt::printf with the standard specs (#1595, #1682, #1683, #1687, #1699). Thanks @rimathia.

  • Fixed handling of operator<< overloads that use copyfmt (#1666).

  • Added the FMT_OS CMake option to control inclusion of OS-specific APIs in the fmt target. This can be useful for embedded platforms (#1654, #1656). Thanks @kwesolowski (Krzysztof Wesolowski).

  • Replaced FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION with the FMT_FUZZ macro to prevent interferring with fuzzing of projects using {fmt} (#1650). Thanks @asraa (Asra Ali).

  • Fixed compatibility with emscripten (#1636, #1637). Thanks @ArthurSonzogni (Arthur Sonzogni).

  • Improved documentation (#704, #1643, #1660, #1681, #1691, #1706, #1714, #1721, #1739, #1740, #1741, #1751). Thanks @senior7515 (Alexander Gallego), @lsr0 (Lindsay Roberts), @puetzk (Kevin Puetz), @fpelliccioni (Fernando Pelliccioni), Alexey Kuzmenko, @jelly (jelle van der Waa), @claremacrae (Clare Macrae), @jiapengwen (文佳鹏), @gsjaardema (Greg Sjaardema), @alexey-milovidov.

  • Implemented various build configuration fixes and improvements (#1603, #1657, #1702, #1728). Thanks @scramsby (Scott Ramsby), @jtojnar (Jan Tojnar), @orivej (Orivej Desh), @flagarde.

  • Fixed various warnings and compilation issues (#1616, #1620, #1622, #1625, #1627, #1628, #1629, #1631, #1633, #1649, #1658, #1661, #1667, #1668, #1669, #1692, #1696, #1697, #1707, #1712, #1716, #1722, #1724, #1729, #1738, #1742, #1743, #1744, #1747, #1750). Thanks @gsjaardema (Greg Sjaardema), @gabime (Gabi Melman), @johnor (Johan), @Kurkin (Dmitry Kurkin), @invexed (James Beach), @peterbell10, @daixtrose (Markus Werle), @petrutlucian94 (Lucian Petrut), @Neargye (Daniil Goncharov), @ambitslix (Attila M. Szilagyi), @gabime (Gabi Melman), @erthink (Leonid Yuriev), @tohammer (Tobias Hammer), @0x8000-0000 (Florin Iucha).

6.2.1 - 2020-05-09

  • Fixed ostream support in sprintf (#1631).
  • Fixed type detection when using implicit conversion to string_view and ostream operator<< inconsistently (#1662).

6.2.0 - 2020-04-05

6.1.2 - 2019-12-11

6.1.1 - 2019-12-04

6.1.0 - 2019-12-01

6.0.0 - 2019-08-26

5.3.0 - 2018-12-28

  • Introduced experimental chrono formatting support:

    #include <fmt/chrono.h>

int main() {
  using namespace std::literals::chrono_literals;
  fmt::print("Default format: {} {}\n", 42s, 100ms);
  fmt::print("strftime-like format: {:%H:%M:%S}\n", 3h + 15min + 30s);
}

    prints:

    Default format: 42s 100ms
strftime-like format: 03:15:30

  • Added experimental support for emphasis (bold, italic, underline, strikethrough), colored output to a file stream, and improved colored formatting API (#961, #967, #973):

    #include <fmt/color.h>

int main() {
  print(fg(fmt::color::crimson) | fmt::emphasis::bold,
        "Hello, {}!\n", "world");
  print(fg(fmt::color::floral_white) | bg(fmt::color::slate_gray) |
        fmt::emphasis::underline, "Hello, {}!\n", "мир");
  print(fg(fmt::color::steel_blue) | fmt::emphasis::italic,
        "Hello, {}!\n", "世界");
}

    prints the following on modern terminals with RGB color support:

    https://user-images.githubusercontent.com/576385/50405788-b66e7500-076e-11e9-9592-7324d1f951d8.png

    Thanks @Rakete1111 (Nicolas).

  • Added support for 4-bit terminal colors (#968, #974)

    #include <fmt/color.h>

int main() {
  print(fg(fmt::terminal_color::red), "stop\n");
}

    Note that these colors vary by terminal:

    https://user-images.githubusercontent.com/576385/50405925-dbfc7e00-0770-11e9-9b85-333fab0af9ac.png

    Thanks @Rakete1111 (Nicolas).

  • Parameterized formatting functions on the type of the format string (#880, #881, #883, #885, #897, #920). Any object of type S that has an overloaded to_string_view(const S&) returning fmt::string_view can be used as a format string:

    namespace my_ns {
inline string_view to_string_view(const my_string& s) {
  return {s.data(), s.length()};
}
}

std::string message = fmt::format(my_string("The answer is {}."), 42);

    Thanks @DanielaE (Daniela Engert).

  • Made std::string_view work as a format string (#898):

    auto message = fmt::format(std::string_view("The answer is {}."), 42);

    Thanks @DanielaE (Daniela Engert).

  • Added wide string support to compile-time format string checks (#924):

    print(fmt(L"{:f}"), 42); // compile-time error: invalid type specifier

    Thanks @XZiar.

  • Made colored print functions work with wide strings (#867):

    #include <fmt/color.h>

int main() {
  print(fg(fmt::color::red), L"{}\n", 42);
}

    Thanks @DanielaE (Daniela Engert).

  • Introduced experimental Unicode support (#628, #891):

    using namespace fmt::literals;
auto s = fmt::format("{:*^5}"_u, "🤡"_u); // s == "**🤡**"_u

  • Improved locale support:

    #include <fmt/locale.h>

struct numpunct : std::numpunct<char> {
 protected:
  char do_thousands_sep() const override { return '~'; }
};

std::locale loc;
auto s = fmt::format(std::locale(loc, new numpunct()), "{:n}", 1234567);
// s == "1~234~567"

  • Constrained formatting functions on proper iterator types (#921). Thanks @DanielaE (Daniela Engert).

  • Added make_printf_args and make_wprintf_args functions (#934). Thanks @tnovotny.

  • Deprecated fmt::visit, parse_context, and wparse_context. Use fmt::visit_format_arg, format_parse_context, and wformat_parse_context instead.

  • Removed undocumented basic_fixed_buffer which has been superseded by the iterator-based API (#873, #902). Thanks @superfunc (hollywood programmer).

  • Disallowed repeated leading zeros in an argument ID:

    fmt::print("{000}", 42); // error

  • Reintroduced support for gcc 4.4.

  • Fixed compilation on platforms with exotic double (#878).

  • Improved documentation (#164, #877, #901, #906, #979). Thanks @kookjr (Mathew Cucuzella), @DarkDimius (Dmitry Petrashko), @HecticSerenity.

  • Added pkgconfig support which makes it easier to consume the library from meson and other build systems (#916). Thanks @colemickens (Cole Mickens).

  • Various build improvements (#909, #926, #937, #953, #959). Thanks @tchaikov (Kefu Chai), @luncliff (Park DongHa), @AndreasSchoenle (Andreas Schönle), @hotwatermorning, @Zefz (JohanJansen).

  • Improved string_view construction performance (#914). Thanks @gabime (Gabi Melman).

  • Fixed non-matching char types (#895). Thanks @DanielaE (Daniela Engert).

  • Fixed format_to_n with std::back_insert_iterator (#913). Thanks @DanielaE (Daniela Engert).

  • Fixed locale-dependent formatting (#905).

  • Fixed various compiler warnings and errors (#882, #886, #933, #941, #931, #943, #954, #956, #962, #965, #977, #983, #989). Thanks @Luthaf (Guillaume Fraux), @stevenhoving (Steven Hoving), @christinaa (Kristina Brooks), @lgritz (Larry Gritz), @DanielaE (Daniela Engert), @0x8000-0000 (Sign Bit), @liuping1997.

5.2.1 - 2018-09-21

5.2.0 - 2018-09-13

  • Optimized format string parsing and argument processing which resulted in up to 5x speed up on long format strings and significant performance boost on various benchmarks. For example, version 5.2 is 2.22x faster than 5.1 on decimal integer formatting with format_to (macOS, clang-902.0.39.2):

    Method

    Time, s

    Speedup

    fmt::format 5.1

    0.58

    		  

    fmt::format 5.2

    0.35

    1.66x

    fmt::format_to 5.1

    0.51

    		  

    fmt::format_to 5.2

    0.23

    2.22x

    sprintf

    0.71

    		  

    std::to_string

    1.01

    		  

    std::stringstream

    1.73

    		  

  • Changed the fmt macro from opt-out to opt-in to prevent name collisions. To enable it define the FMT_STRING_ALIAS macro to 1 before including fmt/format.h:

    #define FMT_STRING_ALIAS 1
#include <fmt/format.h>
std::string answer = format(fmt("{}"), 42);

  • Added compile-time format string checks to format_to overload that takes fmt::memory_buffer (#783):

    fmt::memory_buffer buf;
// Compile-time error: invalid type specifier.
fmt::format_to(buf, fmt("{:d}"), "foo");

  • Moved experimental color support to fmt/color.h and enabled the new API by default. The old API can be enabled by defining the FMT_DEPRECATED_COLORS macro.

  • Added formatting support for types explicitly convertible to fmt::string_view:

    struct foo {
  explicit operator fmt::string_view() const { return "foo"; }
};
auto s = format("{}", foo());

    In particular, this makes formatting function work with folly::StringPiece.

  • Implemented preliminary support for char*_t by replacing the format function overloads with a single function template parameterized on the string type.

  • Added support for dynamic argument lists (#814, #819). Thanks @MikePopoloski (Michael Popoloski).

  • Reduced executable size overhead for embedded targets using newlib nano by making locale dependency optional (#839). Thanks @teajay-fr (Thomas Benard).

  • Keep noexcept specifier when exceptions are disabled (#801, #810). Thanks @qis (Alexej Harm).

  • Fixed formatting of user-defined types providing operator<< with format_to_n (#806). Thanks @mkurdej (Marek Kurdej).

  • Fixed dynamic linkage of new symbols (#808).

  • Fixed global initialization issue (#807):

    // This works on compilers with constexpr support.
static const std::string answer = fmt::format("{}", 42);

  • Fixed various compiler warnings and errors (#804, #809, #811, #822, #827, #830, #838, #843, #844, #851, #852, #854). Thanks @henryiii (Henry Schreiner), @medithe, and @eliasdaler (Elias Daler).

5.1.0 - 2018-07-05

  • Added experimental support for RGB color output enabled with the FMT_EXTENDED_COLORS macro:

    #define FMT_EXTENDED_COLORS
#define FMT_HEADER_ONLY // or compile fmt with FMT_EXTENDED_COLORS defined
#include <fmt/format.h>

fmt::print(fmt::color::steel_blue, "Some beautiful text");

    The old API (the print_colored and vprint_colored functions and the color enum) is now deprecated. (#762 #767). thanks @Remotion (Remo).

  • Added quotes to strings in ranges and tuples (#766). Thanks @Remotion (Remo).

  • Made format_to work with basic_memory_buffer (#776).

  • Added vformat_to_n and wchar_t overload of format_to_n (#764, #769).

  • Made is_range and is_tuple_like part of public (experimental) API to allow specialization for user-defined types (#751, #759). Thanks @drrlvn (Dror Levin).

  • Added more compilers to continuous integration and increased FMT_PEDANTIC warning levels (#736). Thanks @eliaskosunen (Elias Kosunen).

  • Fixed compilation with MSVC 2013.

  • Fixed handling of user-defined types in format_to (#793).

  • Forced linking of inline vformat functions into the library (#795).

  • Fixed incorrect call to on_align in '{:}=' (#750).

  • Fixed floating-point formatting to a non-back_insert_iterator with sign & numeric alignment specified (#756).

  • Fixed formatting to an array with format_to_n (#778).

  • Fixed formatting of more than 15 named arguments (#754).

  • Fixed handling of compile-time strings when including fmt/ostream.h. (#768).

  • Fixed various compiler warnings and errors (#742, #748, #752, #770, #775, #779, #780, #790, #792, #800). Thanks @Remotion (Remo), @gabime (Gabi Melman), @foonathan (Jonathan Müller), @Dark-Passenger (Dhruv Paranjape), and @0x8000-0000 (Sign Bit).

5.0.0 - 2018-05-21

  • Added a requirement for partial C++11 support, most importantly variadic templates and type traits, and dropped FMT_VARIADIC_* emulation macros. Variadic templates are available since GCC 4.4, Clang 2.9 and MSVC 18.0 (2013). For older compilers use {fmt} version 4.x which continues to be maintained and works with C++98 compilers.

  • Renamed symbols to follow standard C++ naming conventions and proposed a subset of the library for standardization in P0645R2 Text Formatting.

  • Implemented constexpr parsing of format strings and compile-time format string checks. For example

    #include <fmt/format.h>

std::string s = format(fmt("{:d}"), "foo");

    gives a compile-time error because d is an invalid specifier for strings (godbolt):

    ...
<source>:4:19: note: in instantiation of function template specialization 'fmt::v5::format<S, char [4]>' requested here
  std::string s = format(fmt("{:d}"), "foo");
                  ^
format.h:1337:13: note: non-constexpr function 'on_error' cannot be used in a constant expression
    handler.on_error("invalid type specifier");

    Compile-time checks require relaxed constexpr (C++14 feature) support. If the latter is not available, checks will be performed at runtime.

  • Separated format string parsing and formatting in the extension API to enable compile-time format string processing. For example

    struct Answer {};

namespace fmt {
template <>
struct formatter<Answer> {
  constexpr auto parse(parse_context& ctx) {
    auto it = ctx.begin();
    spec = *it;
    if (spec != 'd' && spec != 's')
      throw format_error("invalid specifier");
    return ++it;
  }

  template <typename FormatContext>
  auto format(Answer, FormatContext& ctx) {
    return spec == 's' ?
      format_to(ctx.begin(), "{}", "fourty-two") :
      format_to(ctx.begin(), "{}", 42);
  }

  char spec = 0;
};
}

std::string s = format(fmt("{:x}"), Answer());

    gives a compile-time error due to invalid format specifier (godbolt):

    ...
<source>:12:45: error: expression '<throw-expression>' is not a constant expression
       throw format_error("invalid specifier");

  • Added iterator support:

    #include <vector>
#include <fmt/format.h>

std::vector<char> out;
fmt::format_to(std::back_inserter(out), "{}", 42);

  • Added the format_to_n function that restricts the output to the specified number of characters (#298):

    char out[4];
fmt::format_to_n(out, sizeof(out), "{}", 12345);
// out == "1234" (without terminating '\0')

  • Added the formatted_size function for computing the output size:

    #include <fmt/format.h>

auto size = fmt::formatted_size("{}", 12345); // size == 5

  • Improved compile times by reducing dependencies on standard headers and providing a lightweight core API:

    #include <fmt/core.h>

fmt::print("The answer is {}.", 42);

    See Compile time and code bloat.

  • Added the make_format_args function for capturing formatting arguments:

    // Prints formatted error message.
void vreport_error(const char *format, fmt::format_args args) {
  fmt::print("Error: ");
  fmt::vprint(format, args);
}
template <typename... Args>
void report_error(const char *format, const Args & ... args) {
  vreport_error(format, fmt::make_format_args(args...));
}

  • Added the make_printf_args function for capturing printf arguments (#687, #694). Thanks @Kronuz (Germán Méndez Bravo).

  • Added prefix v to non-variadic functions taking format_args to distinguish them from variadic ones:

    std::string vformat(string_view format_str, format_args args);

template <typename... Args>
std::string format(string_view format_str, const Args & ... args);

  • Added experimental support for formatting ranges, containers and tuple-like types in fmt/ranges.h (#735):

    #include <fmt/ranges.h>

std::vector<int> v = {1, 2, 3};
fmt::print("{}", v); // prints {1, 2, 3}

    Thanks @Remotion (Remo).

  • Implemented wchar_t date and time formatting (#712):

    #include <fmt/time.h>

std::time_t t = std::time(nullptr);
auto s = fmt::format(L"The date is {:%Y-%m-%d}.", *std::localtime(&t));

    Thanks @DanielaE (Daniela Engert).

  • Provided more wide string overloads (#724). Thanks @DanielaE (Daniela Engert).

  • Switched from a custom null-terminated string view class to string_view in the format API and provided fmt::string_view which implements a subset of std::string_view API for pre-C++17 systems.

  • Added support for std::experimental::string_view (#607):

    #include <fmt/core.h>
#include <experimental/string_view>

fmt::print("{}", std::experimental::string_view("foo"));

    Thanks @virgiliofornazin (Virgilio Alexandre Fornazin).

  • Allowed mixing named and automatic arguments:

    fmt::format("{} {two}", 1, fmt::arg("two", 2));

  • Removed the write API in favor of the format API with compile-time handling of format strings.

  • Disallowed formatting of multibyte strings into a wide character target (#606).

  • Improved documentation (#515, #614, #617, #661, #680). Thanks @ibell (Ian Bell), @mihaitodor (Mihai Todor), and @johnthagen.

  • Implemented more efficient handling of large number of format arguments.

  • Introduced an inline namespace for symbol versioning.

  • Added debug postfix d to the fmt library name (#636).

  • Removed unnecessary fmt/ prefix in includes (#397). Thanks @chronoxor (Ivan Shynkarenka).

  • Moved fmt/*.h to include/fmt/*.h to prevent irrelevant files and directories appearing on the include search paths when fmt is used as a subproject and moved source files to the src directory.

  • Added qmake project file support/fmt.pro (#641). Thanks @cowo78 (Giuseppe Corbelli).

  • Added Gradle build file support/build.gradle (#649). Thanks @luncliff (Park DongHa).

  • Removed FMT_CPPFORMAT CMake option.

  • Fixed a name conflict with the macro CHAR_WIDTH in glibc (#616). Thanks @aroig (Abdó Roig-Maranges).

  • Fixed handling of nested braces in fmt::join (#638).

  • Added SOURCELINK_SUFFIX for compatibility with Sphinx 1.5 (#497). Thanks @ginggs (Graham Inggs).

  • Added a missing inline in the header-only mode (#626). Thanks @aroig (Abdó Roig-Maranges).

  • Fixed various compiler warnings (#640, #656, #679, #681, #705, #715, #717, #720, #723, #726, #730, #739). Thanks @peterbell10, @LarsGullik, @foonathan (Jonathan Müller), @eliaskosunen (Elias Kosunen), @christianparpart (Christian Parpart), @DanielaE (Daniela Engert), and @mwinterb.

  • Worked around an MSVC bug and fixed several warnings (#653). Thanks @alabuzhev (Alex Alabuzhev).

  • Worked around GCC bug 67371 (#682).

  • Fixed compilation with -fno-exceptions (#655). Thanks @chenxiaolong (Andrew Gunnerson).

  • Made constexpr remove_prefix gcc version check tighter (#648).

  • Renamed internal type enum constants to prevent collision with poorly written C libraries (#644).

  • Added detection of wostream operator<< (#650).

  • Fixed compilation on OpenBSD (#660). Thanks @hubslave.

  • Fixed compilation on FreeBSD 12 (#732). Thanks @dankm.

  • Fixed compilation when there is a mismatch between -std options between the library and user code (#664).

  • Fixed compilation with GCC 7 and -std=c++11 (#734).

  • Improved generated binary code on GCC 7 and older (#668).

  • Fixed handling of numeric alignment with no width (#675).

  • Fixed handling of empty strings in UTF8/16 converters (#676). Thanks @vgalka-sl (Vasili Galka).

  • Fixed formatting of an empty string_view (#689).

  • Fixed detection of string_view on libc++ (#686).

  • Fixed DLL issues (#696). Thanks @sebkoenig.

  • Fixed compile checks for mixing narrow and wide strings (#690).

  • Disabled unsafe implicit conversion to std::string (#729).

  • Fixed handling of reused format specs (as in fmt::join) for pointers (#725). Thanks @mwinterb.

  • Fixed installation of fmt/ranges.h (#738). Thanks @sv1990.

4.1.0 - 2017-12-20

4.0.0 - 2017-06-27

3.0.2 - 2017-06-14

3.0.1 - 2016-11-01

3.0.0 - 2016-05-07

  • The project has been renamed from C++ Format (cppformat) to fmt for consistency with the used namespace and macro prefix (#307). Library headers are now located in the fmt directory:

    #include "fmt/format.h"

    Including format.h from the cppformat directory is deprecated but works via a proxy header which will be removed in the next major version.

    The documentation is now available at https://fmt.dev.

  • Added support for strftime-like date and time formatting (#283):

    #include "fmt/time.h"

std::time_t t = std::time(nullptr);
// Prints "The date is 2016-04-29." (with the current date)
fmt::print("The date is {:%Y-%m-%d}.", *std::localtime(&t));

  • std::ostream support including formatting of user-defined types that provide overloaded operator<< has been moved to fmt/ostream.h:

    #include "fmt/ostream.h"

class Date {
  int year_, month_, day_;
public:
  Date(int year, int month, int day) : year_(year), month_(month), day_(day) {}

  friend std::ostream &operator<<(std::ostream &os, const Date &d) {
    return os << d.year_ << '-' << d.month_ << '-' << d.day_;
  }
};

std::string s = fmt::format("The date is {}", Date(2012, 12, 9));
// s == "The date is 2012-12-9"

  • Added support for custom argument formatters (#235).

  • Added support for locale-specific integer formatting with the n specifier (#305):

    std::setlocale(LC_ALL, "en_US.utf8");
fmt::print("cppformat: {:n}\n", 1234567); // prints 1,234,567

  • Sign is now preserved when formatting an integer with an incorrect printf format specifier (#265):

    fmt::printf("%lld", -42); // prints -42

    Note that it would be an undefined behavior in std::printf.

  • Length modifiers such as ll are now optional in printf formatting functions and the correct type is determined automatically (#255):

    fmt::printf("%d", std::numeric_limits<long long>::max());

    Note that it would be an undefined behavior in std::printf.

  • Added initial support for custom formatters (#231).

  • Fixed detection of user-defined literal support on Intel C++ compiler (#311, #312). Thanks to @dean0x7d (Dean Moldovan) and @speth (Ray Speth).

  • Reduced compile time (#243, #249, #317):

    https://cloud.githubusercontent.com/assets/4831417/11614060/b9e826d2-9c36-11e5-8666-d4131bf503ef.png https://cloud.githubusercontent.com/assets/4831417/11614080/6ac903cc-9c37-11e5-8165-26df6efae364.png

    Thanks to @dean0x7d (Dean Moldovan).

  • Compile test fixes (#313). Thanks to @dean0x7d (Dean Moldovan).

  • Documentation fixes (#239, #248, #252, #258, #260, #301, #309). Thanks to @ReadmeCritic @Gachapen (Magnus Bjerke Vik) and @jwilk (Jakub Wilk).

  • Fixed compiler and sanitizer warnings (#244, #256, #259, #263, #274, #277, #286, #291, #296, #308) Thanks to @mwinterb, @pweiskircher (Patrik Weiskircher), @Naios.

  • Improved compatibility with Windows Store apps (#280, #285) Thanks to @mwinterb.

  • Added tests of compatibility with older C++ standards (#273). Thanks to @niosHD.

  • Fixed Android build (#271). Thanks to @newnon.

  • Changed ArgMap to be backed by a vector instead of a map. (#261, #262). Thanks to @mwinterb.

  • Added fprintf overload that writes to a std::ostream (#251). Thanks to nickhutchinson (Nicholas Hutchinson).

  • Export symbols when building a Windows DLL (#245). Thanks to macdems (Maciek Dems).

  • Fixed compilation on Cygwin (#304).

  • Implemented a workaround for a bug in Apple LLVM version 4.2 of clang (#276).

  • Implemented a workaround for Google Test bug #705 on gcc 6 (#268). Thanks to octoploid.

  • Removed Biicode support because the latter has been discontinued.

2.1.1 - 2016-04-11

  • The install location for generated CMake files is now configurable via the FMT_CMAKE_DIR CMake variable (#299). Thanks to @niosHD.
  • Documentation fixes (#252).

2.1.0 - 2016-03-21

  • Project layout and build system improvements (#267):

    • The code have been moved to the cppformat directory. Including format.h from the top-level directory is deprecated but works via a proxy header which will be removed in the next major version.
    • C++ Format CMake targets now have proper interface definitions.
    • Installed version of the library now supports the header-only configuration.
    • Targets doc, install, and test are now disabled if C++ Format is included as a CMake subproject. They can be enabled by setting FMT_DOC, FMT_INSTALL, and FMT_TEST in the parent project.

    Thanks to @niosHD.

2.0.1 - 2016-03-13

2.0.0 - 2015-12-01

General

  • [Breaking] Named arguments (#169, #173, #174):

    fmt::print("The answer is {answer}.", fmt::arg("answer", 42));

    Thanks to @jamboree.

  • [Experimental] User-defined literals for format and named arguments (#204, #206, #207):

    using namespace fmt::literals;
fmt::print("The answer is {answer}.", "answer"_a=42);

    Thanks to @dean0x7d (Dean Moldovan).

  • [Breaking] Formatting of more than 16 arguments is now supported when using variadic templates (#141). Thanks to @Shauren.

  • Runtime width specification (#168):

    fmt::format("{0:{1}}", 42, 5); // gives "   42"

    Thanks to @jamboree.

  • [Breaking] Enums are now formatted with an overloaded std::ostream insertion operator (operator<<) if available (#232).

  • [Breaking] Changed default bool format to textual, "true" or "false" (#170):

    fmt::print("{}", true); // prints "true"

    To print bool as a number use numeric format specifier such as d:

    fmt::print("{:d}", true); // prints "1"

  • fmt::printf and fmt::sprintf now support formatting of bool with the %s specifier giving textual output, "true" or "false" (#223):

    fmt::printf("%s", true); // prints "true"

    Thanks to @LarsGullik.

  • [Breaking] signed char and unsigned char are now formatted as integers by default (#217).

  • [Breaking] Pointers to C strings can now be formatted with the p specifier (#223):

    fmt::print("{:p}", "test"); // prints pointer value

    Thanks to @LarsGullik.

  • [Breaking] fmt::printf and fmt::sprintf now print null pointers as (nil) and null strings as (null) for consistency with glibc (#226). Thanks to @LarsGullik.

  • [Breaking] fmt::(s)printf now supports formatting of objects of user-defined types that provide an overloaded std::ostream insertion operator (operator<<) (#201):

    fmt::printf("The date is %s", Date(2012, 12, 9));

  • [Breaking] The Buffer template is now part of the public API and can be used to implement custom memory buffers (#140). Thanks to @polyvertex (Jean-Charles Lefebvre).

  • [Breaking] Improved compatibility between BasicStringRef and std::experimental::basic_string_view (#100, #159, #183):

    • Comparison operators now compare string content, not pointers
    • BasicStringRef::c_str replaced by BasicStringRef::data
    • BasicStringRef is no longer assumed to be null-terminated

    References to null-terminated strings are now represented by a new class, BasicCStringRef.

  • Dependency on pthreads introduced by Google Test is now optional (#185).

  • New CMake options FMT_DOC, FMT_INSTALL and FMT_TEST to control generation of doc, install and test targets respectively, on by default (#197, #198, #200). Thanks to @maddinat0r (Alex Martin).

  • noexcept is now used when compiling with MSVC2015 (#215). Thanks to @dmkrepo (Dmitriy).

  • Added an option to disable use of windows.h when FMT_USE_WINDOWS_H is defined as 0 before including format.h (#171). Thanks to @alfps (Alf P. Steinbach).

  • [Breaking] windows.h is now included with NOMINMAX unless FMT_WIN_MINMAX is defined. This is done to prevent breaking code using std::min and std::max and only affects the header-only configuration (#152, #153, #154). Thanks to @DevO2012.

  • Improved support for custom character types (#171). Thanks to @alfps (Alf P. Steinbach).

  • Added an option to disable use of IOStreams when FMT_USE_IOSTREAMS is defined as 0 before including format.h (#205, #208). Thanks to @JodiTheTigger.

  • Improved detection of isnan, isinf and signbit.

Optimization

  • Made formatting of user-defined types more efficient with a custom stream buffer (#92, #230). Thanks to @NotImplemented.
  • Further improved performance of fmt::Writer on integer formatting and fixed a minor regression. Now it is ~7% faster than karma::generate on Karma's benchmark (#186).
  • [Breaking] Reduced compiled code size (#143, #149).

Distribution

Documentation

Fixes

1.1.0 - 2015-03-06

  • Added BasicArrayWriter, a class template that provides operations for formatting and writing data into a fixed-size array (#105 and #122):

    char buffer[100];
fmt::ArrayWriter w(buffer);
w.write("The answer is {}", 42);

  • Added 0 A.D. and PenUltima Online (POL) to the list of notable projects using C++ Format.

  • C++ Format now uses MSVC intrinsics for better formatting performance (#115, #116, #118 and #121). Previously these optimizations where only used on GCC and Clang. Thanks to @CarterLi and @objectx.

  • CMake install target (#119). Thanks to @TrentHouliston.

    You can now install C++ Format with make install command.

  • Improved Biicode support (#98 and #104). Thanks to @MariadeAnton and @franramirez688.

  • Improved support for building with Android NDK (#107). Thanks to @newnon.

    The android-ndk-example repository provides and example of using C++ Format with Android NDK:

    https://raw.githubusercontent.com/fmtlib/android-ndk-example/master/screenshot.png

  • Improved documentation of SystemError and WindowsError (#54).

  • Various code improvements (#110, #111 #112). Thanks to @CarterLi.

  • Improved compile-time errors when formatting wide into narrow strings (#117).

  • Fixed BasicWriter::write without formatting arguments when C++11 support is disabled (#109).

  • Fixed header-only build on OS X with GCC 4.9 (#124).

  • Fixed packaging issues (#94).

  • Added changelog (#103).

1.0.0 - 2015-02-05

  • Add support for a header-only configuration when FMT_HEADER_ONLY is defined before including format.h:

    #define FMT_HEADER_ONLY
#include "format.h"

  • Compute string length in the constructor of BasicStringRef instead of the size method (#79). This eliminates size computation for string literals on reasonable optimizing compilers.

  • Fix formatting of types with overloaded operator << for std::wostream (#86):

    fmt::format(L"The date is {0}", Date(2012, 12, 9));

  • Fix linkage of tests on Arch Linux (#89).

  • Allow precision specifier for non-float arguments (#90):

    fmt::print("{:.3}\n", "Carpet"); // prints "Car"

  • Fix build on Android NDK (#93)

  • Improvements to documentation build procedure.

  • Remove FMT_SHARED CMake variable in favor of standard BUILD_SHARED_LIBS.

  • Fix error handling in fmt::fprintf.

  • Fix a number of warnings.

0.12.0 - 2014-10-25

  • [Breaking] Improved separation between formatting and buffer management. Writer is now a base class that cannot be instantiated directly. The new MemoryWriter class implements the default buffer management with small allocations done on stack. So fmt::Writer should be replaced with fmt::MemoryWriter in variable declarations.

    Old code:

    fmt::Writer w;

    New code:

    fmt::MemoryWriter w;

    If you pass fmt::Writer by reference, you can continue to do so:

    void f(fmt::Writer &w);

    This doesn't affect the formatting API.

  • Support for custom memory allocators (#69)

  • Formatting functions now accept signed char and unsigned char strings as arguments (#73):

    auto s = format("GLSL version: {}", glGetString(GL_VERSION));

  • Reduced code bloat. According to the new benchmark results, cppformat is close to printf and by the order of magnitude better than Boost Format in terms of compiled code size.

  • Improved appearance of the documentation on mobile by using the Sphinx Bootstrap theme:

    Old

    New

    old

    new

0.11.0 - 2014-08-21

  • Safe printf implementation with a POSIX extension for positional arguments:

    fmt::printf("Elapsed time: %.2f seconds", 1.23);
fmt::printf("%1$s, %3$d %2$s", weekday, month, day);

  • Arguments of char type can now be formatted as integers (Issue #55):

    fmt::format("0x{0:02X}", 'a');

  • Deprecated parts of the API removed.

  • The library is now built and tested on MinGW with Appveyor in addition to existing test platforms Linux/GCC, OS X/Clang, Windows/MSVC.

0.10.0 - 2014-07-01

Improved API

  • All formatting methods are now implemented as variadic functions instead of using operator<< for feeding arbitrary arguments into a temporary formatter object. This works both with C++11 where variadic templates are used and with older standards where variadic functions are emulated by providing lightweight wrapper functions defined with the FMT_VARIADIC macro. You can use this macro for defining your own portable variadic functions:

    void report_error(const char *format, const fmt::ArgList &args) {
  fmt::print("Error: {}");
  fmt::print(format, args);
}
FMT_VARIADIC(void, report_error, const char *)

report_error("file not found: {}", path);

    Apart from a more natural syntax, this also improves performance as there is no need to construct temporary formatter objects and control arguments' lifetimes. Because the wrapper functions are very lightweight, this doesn't cause code bloat even in pre-C++11 mode.

  • Simplified common case of formatting an std::string. Now it requires a single function call:

    std::string s = format("The answer is {}.", 42);

    Previously it required 2 function calls:

    std::string s = str(Format("The answer is {}.") << 42);

    Instead of unsafe c_str function, fmt::Writer should be used directly to bypass creation of std::string:

    fmt::Writer w;
w.write("The answer is {}.", 42);
w.c_str();  // returns a C string

    This doesn't do dynamic memory allocation for small strings and is less error prone as the lifetime of the string is the same as for std::string::c_str which is well understood (hopefully).

  • Improved consistency in naming functions that are a part of the public API. Now all public functions are lowercase following the standard library conventions. Previously it was a combination of lowercase and CapitalizedWords. Issue #50.

  • Old functions are marked as deprecated and will be removed in the next release.

Other Changes

  • Experimental support for printf format specifications (work in progress):

    fmt::printf("The answer is %d.", 42);
std::string s = fmt::sprintf("Look, a %s!", "string");

  • Support for hexadecimal floating point format specifiers a and A:

    print("{:a}", -42.0); // Prints -0x1.5p+5
print("{:A}", -42.0); // Prints -0X1.5P+5

  • CMake option FMT_SHARED that specifies whether to build format as a shared library (off by default).

0.9.0 - 2014-05-13

  • More efficient implementation of variadic formatting functions.

  • Writer::Format now has a variadic overload:

    Writer out;
out.Format("Look, I'm {}!", "variadic");

  • For efficiency and consistency with other overloads, variadic overload of the Format function now returns Writer instead of std::string. Use the str function to convert it to std::string:

    std::string s = str(Format("Look, I'm {}!", "variadic"));

  • Replaced formatter actions with output sinks: NoAction -> NullSink, Write -> FileSink, ColorWriter -> ANSITerminalSink. This improves naming consistency and shouldn't affect client code unless these classes are used directly which should be rarely needed.

  • Added ThrowSystemError function that formats a message and throws SystemError containing the formatted message and system-specific error description. For example, the following code

    FILE *f = fopen(filename, "r");
if (!f)
  ThrowSystemError(errno, "Failed to open file '{}'") << filename;

    will throw SystemError exception with description "Failed to open file '<filename>': No such file or directory" if file doesn't exist.

  • Support for AppVeyor continuous integration platform.

  • Format now throws SystemError in case of I/O errors.

  • Improve test infrastructure. Print functions are now tested by redirecting the output to a pipe.

0.8.0 - 2014-04-14

  • Initial release