Bump msys2/setup-msys2 from 2.27.0 to 2.28.0 (#4485)
Bumps msys2/setup-msys2 from 2.27.0 to 2.28.0.
updated-dependencies:
- dependency-name: msys2/setup-msys2 dependency-version: 2.28.0 dependency-type: direct:production update-type: version-update:semver-minor …
Signed-off-by: dependabot[bot] support@github.com Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
{fmt} is an open-source formatting library providing a fast and safe alternative to C stdio and C++ iostreams.
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Documentation
Cheat Sheets
Q&A: ask questions on StackOverflow with the tag fmt.
Try {fmt} in Compiler Explorer.
Features
(s)printf
, iostreams,to_string
andto_chars
, see Speed tests and Converting a hundred million integers to strings per secondbase.h
,format.h
andformat-inl.h
, and compiled code; see Compile time and code bloat-Wall -Wextra -pedantic
FMT_HEADER_ONLY
macroSee the documentation for more details.
Examples
Print to stdout (run)
Format a string (run)
Format a string using positional arguments (run)
Print dates and times (run)
Output:
Print a container (run)
Output:
Check a format string at compile time
This gives a compile-time error in C++20 because
d
is an invalid format specifier for a string.Write a file from a single thread
This can be 5 to 9 times faster than fprintf.
Print with colors and text styles
Output on a modern terminal with Unicode support:
Benchmarks
Speed tests
{fmt} is the fastest of the benchmarked methods, ~20% faster than
printf
.The above results were generated by building
tinyformat_test.cpp
on macOS 12.6.1 withclang++ -O3 -DNDEBUG -DSPEED_TEST -DHAVE_FORMAT
, and taking the best of three runs. In the test, the format string"%0.10f:%04d:%+g:%s:%p:%c:%%\n"
or equivalent is filled 2,000,000 times with output sent to/dev/null
; for further details refer to the source.{fmt} is up to 20-30x faster than
std::ostringstream
andsprintf
on IEEE754float
anddouble
formatting (dtoa-benchmark) and faster than double-conversion and ryu:Compile time and code bloat
The script bloat-test.py from format-benchmark tests compile time and code bloat for nontrivial projects. It generates 100 translation units and uses
printf()
or its alternative five times in each to simulate a medium-sized project. The resulting executable size and compile time (Apple clang version 15.0.0 (clang-1500.1.0.2.5), macOS Sonoma, best of three) is shown in the following tables.Optimized build (-O3)
{fmt} is fast to compile and is comparable to
printf
in terms of per-call binary size (within a rounding error on this system).Non-optimized build
libc
,lib(std)c++
, andlibfmt
are all linked as shared libraries to compare formatting function overhead only. Boost Format is a header-only library so it doesn't provide any linkage options.Running the tests
Please refer to Building the library for instructions on how to build the library and run the unit tests.
Benchmarks reside in a separate repository, format-benchmarks, so to run the benchmarks you first need to clone this repository and generate Makefiles with CMake:
Then you can run the speed test:
or the bloat test:
Migrating code
clang-tidy v18 provides the modernize-use-std-print check that is capable of converting occurrences of
printf
andfprintf
tofmt::print
if configured to do so. (By default it converts tostd::print
.)Notable projects using this library
More...
If you are aware of other projects using this library, please let me know by email or by submitting an issue.
Motivation
So why yet another formatting library?
There are plenty of methods for doing this task, from standard ones like the printf family of function and iostreams to Boost Format and FastFormat libraries. The reason for creating a new library is that every existing solution that I found either had serious issues or didn't provide all the features I needed.
printf
The good thing about
printf
is that it is pretty fast and readily available being a part of the C standard library. The main drawback is that it doesn't support user-defined types.printf
also has safety issues although they are somewhat mitigated with __attribute__ ((format (printf, ...)) in GCC. There is a POSIX extension that adds positional arguments required for i18n toprintf
but it is not a part of C99 and may not be available on some platforms.iostreams
The main issue with iostreams is best illustrated with an example:
which is a lot of typing compared to printf:
Matthew Wilson, the author of FastFormat, called this "chevron hell". iostreams don't support positional arguments by design.
The good part is that iostreams support user-defined types and are safe although error handling is awkward.
Boost Format
This is a very powerful library that supports both
printf
-like format strings and positional arguments. Its main drawback is performance. According to various benchmarks, it is much slower than other methods considered here. Boost Format also has excessive build times and severe code bloat issues (see Benchmarks).FastFormat
This is an interesting library that is fast, safe and has positional arguments. However, it has significant limitations, citing its author:
It is also quite big and has a heavy dependency, on STLSoft, which might be too restrictive for use in some projects.
Boost Spirit.Karma
This is not a formatting library but I decided to include it here for completeness. As iostreams, it suffers from the problem of mixing verbatim text with arguments. The library is pretty fast, but slower on integer formatting than
fmt::format_to
with format string compilation on Karma's own benchmark, see Converting a hundred million integers to strings per second.License
{fmt} is distributed under the MIT license.
Documentation License
The Format String Syntax section in the documentation is based on the one from Python string module documentation. For this reason, the documentation is distributed under the Python Software Foundation license available in doc/python-license.txt. It only applies if you distribute the documentation of {fmt}.
Maintainers
The {fmt} library is maintained by Victor Zverovich (vitaut) with contributions from many other people. See Contributors and Releases for some of the names. Let us know if your contribution is not listed or mentioned incorrectly and we'll make it right.
Security Policy
To report a security issue, please disclose it at security advisory.
This project is maintained by a team of volunteers on a reasonable-effort basis. As such, please give us at least 90 days to work on a fix before public exposure.