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: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.