diff --git a/README.md b/README.md new file mode 100644 index 00000000..8b590fcf --- /dev/null +++ b/README.md @@ -0,0 +1,494 @@ +{fmt} + +[![image](https://github.com/fmtlib/fmt/workflows/linux/badge.svg)](https://github.com/fmtlib/fmt/actions?query=workflow%3Alinux) +[![image](https://github.com/fmtlib/fmt/workflows/macos/badge.svg)](https://github.com/fmtlib/fmt/actions?query=workflow%3Amacos) +[![image](https://github.com/fmtlib/fmt/workflows/windows/badge.svg)](https://github.com/fmtlib/fmt/actions?query=workflow%3Awindows) +[![fmt is continuously fuzzed at oss-fuzz](https://oss-fuzz-build-logs.storage.googleapis.com/badges/fmt.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?\%0Acolspec=ID%20Type%20Component%20Status%20Proj%20Reported%20Owner%20\%0ASummary&q=proj%3Dfmt&can=1) +[![Ask questions at StackOverflow with the tag fmt](https://img.shields.io/badge/stackoverflow-fmt-blue.svg)](https://stackoverflow.com/questions/tagged/fmt) +[![image](https://api.securityscorecards.dev/projects/github.com/fmtlib/fmt/badge)](https://securityscorecards.dev/viewer/?uri=github.com/fmtlib/fmt) + +**{fmt}** is an open-source formatting library providing a fast and safe +alternative to C stdio and C++ iostreams. + +If you like this project, please consider donating to one of the funds +that help victims of the war in Ukraine: . + +[Documentation](https://fmt.dev) + +[Cheat Sheets](https://hackingcpp.com/cpp/libs/fmt.html) + +Q&A: ask questions on [StackOverflow with the tag +fmt](https://stackoverflow.com/questions/tagged/fmt). + +Try {fmt} in [Compiler Explorer](https://godbolt.org/z/Eq5763). + +# Features + +- Simple [format API](https://fmt.dev/latest/api.html) with positional + arguments for localization +- Implementation of [C++20 + std::format](https://en.cppreference.com/w/cpp/utility/format) and + [C++23 std::print](https://en.cppreference.com/w/cpp/io/print) +- [Format string syntax](https://fmt.dev/latest/syntax.html) similar + to Python\'s + [format](https://docs.python.org/3/library/stdtypes.html#str.format) +- Fast IEEE 754 floating-point formatter with correct rounding, + shortness and round-trip guarantees using the + [Dragonbox](https://github.com/jk-jeon/dragonbox) algorithm +- Portable Unicode support +- Safe [printf + implementation](https://fmt.dev/latest/api.html#printf-formatting) + including the POSIX extension for positional arguments +- Extensibility: [support for user-defined + types](https://fmt.dev/latest/api.html#formatting-user-defined-types) +- High performance: faster than common standard library + implementations of `(s)printf`, iostreams, `to_string` and + `to_chars`, see [Speed tests](#speed-tests) and [Converting a + hundred million integers to strings per + second](http://www.zverovich.net/2020/06/13/fast-int-to-string-revisited.html) +- Small code size both in terms of source code with the minimum + configuration consisting of just three files, `core.h`, `format.h` + and `format-inl.h`, and compiled code; see [Compile time and code + bloat](#compile-time-and-code-bloat) +- Reliability: the library has an extensive set of + [tests](https://github.com/fmtlib/fmt/tree/master/test) and is + [continuously fuzzed](https://bugs.chromium.org/p/oss-fuzz/issues/list?colspec=ID%20Type%20Component%20Status%20Proj%20Reported%20Owner%20Summary&q=proj%3Dfmt&can=1) +- Safety: the library is fully type-safe, errors in format strings can + be reported at compile time, automatic memory management prevents + buffer overflow errors +- Ease of use: small self-contained code base, no external + dependencies, permissive MIT + [license](https://github.com/fmtlib/fmt/blob/master/LICENSE.rst) +- [Portability](https://fmt.dev/latest/index.html#portability) with + consistent output across platforms and support for older compilers +- Clean warning-free codebase even on high warning levels such as + `-Wall -Wextra -pedantic` +- Locale independence by default +- Optional header-only configuration enabled with the + `FMT_HEADER_ONLY` macro + +See the [documentation](https://fmt.dev) for more details. + +# Examples + +**Print to stdout** ([run](https://godbolt.org/z/Tevcjh)) + +``` c++ +#include + +int main() { + fmt::print("Hello, world!\n"); +} +``` + +**Format a string** ([run](https://godbolt.org/z/oK8h33)) + +``` c++ +std::string s = fmt::format("The answer is {}.", 42); +// s == "The answer is 42." +``` + +**Format a string using positional arguments** +([run](https://godbolt.org/z/Yn7Txe)) + +``` c++ +std::string s = fmt::format("I'd rather be {1} than {0}.", "right", "happy"); +// s == "I'd rather be happy than right." +``` + +**Print chrono durations** ([run](https://godbolt.org/z/K8s4Mc)) + +``` c++ +#include + +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); +} +``` + +Output: + + Default format: 42s 100ms + strftime-like format: 03:15:30 + +**Print a container** ([run](https://godbolt.org/z/MxM1YqjE7)) + +``` c++ +#include +#include + +int main() { + std::vector v = {1, 2, 3}; + fmt::print("{}\n", v); +} +``` + +Output: + + [1, 2, 3] + +**Check a format string at compile time** + +``` c++ +std::string s = fmt::format("{:d}", "I am not a number"); +``` + +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** + +``` c++ +#include + +int main() { + auto out = fmt::output_file("guide.txt"); + out.print("Don't {}", "Panic"); +} +``` + +This can be [5 to 9 times faster than +fprintf](http://www.zverovich.net/2020/08/04/optimal-file-buffer-size.html). + +**Print with colors and text styles** + +``` c++ +#include + +int main() { + fmt::print(fg(fmt::color::crimson) | fmt::emphasis::bold, + "Hello, {}!\n", "world"); + fmt::print(fg(fmt::color::floral_white) | bg(fmt::color::slate_gray) | + fmt::emphasis::underline, "Olá, {}!\n", "Mundo"); + fmt::print(fg(fmt::color::steel_blue) | fmt::emphasis::italic, + "你好{}！\n", "世界"); +} +``` + +Output on a modern terminal with Unicode support: + +![image](https://github.com/fmtlib/fmt/assets/%0A576385/2a93c904-d6fa-4aa6-b453-2618e1c327d7) + +# Benchmarks + +## Speed tests + ++-------------------+---------------+-------------+ +| Library | Method | Run Time, s | ++===================+===============+=============+ +| libc | printf | > 0.91 | ++-------------------+---------------+-------------+ +| libc++ | std::ostream | > 2.49 | ++-------------------+---------------+-------------+ +| {fmt} 9.1 | fmt::print | > 0.74 | ++-------------------+---------------+-------------+ +| Boost Format 1.80 | boost::format | > 6.26 | ++-------------------+---------------+-------------+ +| Folly Format | folly::format | > 1.87 | ++-------------------+---------------+-------------+ + +{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 with `clang++ -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](https://github.com/fmtlib/format-benchmark/blob/master/src/tinyformat-test.cc). + +{fmt} is up to 20-30x faster than `std::ostringstream` and `sprintf` on +IEEE754 `float` and `double` formatting +([dtoa-benchmark](https://github.com/fmtlib/dtoa-benchmark)) and faster +than [double-conversion](https://github.com/google/double-conversion) +and [ryu](https://github.com/ulfjack/ryu): + +[![image](https://user-images.githubusercontent.com/576385/%0A95684665-11719600-0ba8-11eb-8e5b-972ff4e49428.png)](https://fmt.dev/unknown_mac64_clang12.0.html) + +## Compile time and code bloat + +The script +[bloat-test.py](https://github.com/fmtlib/format-benchmark/blob/master/bloat-test.py) +from [format-benchmark](https://github.com/fmtlib/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 LLVM version 8.1.0 (clang-802.0.42), macOS +Sierra, best of three) is shown in the following tables. + +**Optimized build (-O3)** + +| Method | Compile Time, s | Executable size, KiB | Stripped size, KiB | +| ------------- | --------------- | -------------------- | ------------------ | +| printf | > 2.6 | > 29 | > 26 | +| printf+string | > 16.4 | > 29 | > 26 | +| iostreams | > 31.1 | > 59 | > 55 | +| {fmt} | > 19.0 | > 37 | > 34 | +| Boost Format | > 91.9 | > 226 | > 203 | +| Folly Format | > 115.7 | > 101 | > 88 | + +As you can see, {fmt} has 60% less overhead in terms of resulting binary +code size compared to iostreams and comes pretty close to `printf`. +Boost Format and Folly Format have the largest overheads. + +`printf+string` is the same as `printf` but with an extra `` +include to measure the overhead of the latter. + +**Non-optimized build** + +| Method | Compile Time, s | Executable size, KiB | Stripped size, KiB | +| ------------- | --------------- | -------------------- | ------------------ | +| printf | > 2.2 | > 33 | > 30 | +| printf+string | > 16.0 | > 33 | > 30 | +| iostreams | > 28.3 | > 56 | > 52 | +| {fmt} | > 18.2 | > 59 | > 50 | +| Boost Format | > 54.1 | > 365 | > 303 | +| Folly Format | > 79.9 | > 445 | > 430 | + +`libc`, `lib(std)c++`, and `libfmt` 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](https://fmt.dev/latest/usage.html#building-the-library) for +instructions on how to build the library and run the unit tests. + +Benchmarks reside in a separate repository, +[format-benchmarks](https://github.com/fmtlib/format-benchmark), so to +run the benchmarks you first need to clone this repository and generate +Makefiles with CMake: + + $ git clone --recursive https://github.com/fmtlib/format-benchmark.git + $ cd format-benchmark + $ cmake . + +Then you can run the speed test: + + $ make speed-test + +or the bloat test: + + $ make bloat-test + +# Migrating code + +[clang-tidy](https://clang.llvm.org/extra/clang-tidy/) v17 (not yet +released) provides the +[modernize-use-std-print](https://clang.llvm.org/extra/clang-tidy/checks/modernize/use-std-print.html) +check that is capable of converting occurrences of `printf` and +`fprintf` to `fmt::print` if configured to do so. (By default it +converts to `std::print`.) + +# Projects using this library + +- [0 A.D.](https://play0ad.com/): a free, open-source, cross-platform + real-time strategy game +- [AMPL/MP](https://github.com/ampl/mp): an open-source library for + mathematical programming +- [Aseprite](https://github.com/aseprite/aseprite): animated sprite + editor & pixel art tool +- [AvioBook](https://www.aviobook.aero/en): a comprehensive aircraft + operations suite +- [Blizzard Battle.net](https://battle.net/): an online gaming + platform +- [Celestia](https://celestia.space/): real-time 3D visualization of + space +- [Ceph](https://ceph.com/): a scalable distributed storage system +- [ccache](https://ccache.dev/): a compiler cache +- [ClickHouse](https://github.com/ClickHouse/ClickHouse): an + analytical database management system +- [Contour](https://github.com/contour-terminal/contour/): a modern + terminal emulator +- [CUAUV](https://cuauv.org/): Cornell University\'s autonomous + underwater vehicle +- [Drake](https://drake.mit.edu/): a planning, control, and analysis + toolbox for nonlinear dynamical systems (MIT) +- [Envoy](https://lyft.github.io/envoy/): C++ L7 proxy and + communication bus (Lyft) +- [FiveM](https://fivem.net/): a modification framework for GTA V +- [fmtlog](https://github.com/MengRao/fmtlog): a performant + fmtlib-style logging library with latency in nanoseconds +- [Folly](https://github.com/facebook/folly): Facebook open-source + library +- [GemRB](https://gemrb.org/): a portable open-source implementation + of Bioware's Infinity Engine +- [Grand Mountain + Adventure](https://store.steampowered.com/app/1247360/Grand_Mountain_Adventure/): + a beautiful open-world ski & snowboarding game +- [HarpyWar/pvpgn](https://github.com/pvpgn/pvpgn-server): Player vs + Player Gaming Network with tweaks +- [KBEngine](https://github.com/kbengine/kbengine): an open-source + MMOG server engine +- [Keypirinha](https://keypirinha.com/): a semantic launcher for + Windows +- [Kodi](https://kodi.tv/) (formerly xbmc): home theater software +- [Knuth](https://kth.cash/): high-performance Bitcoin full-node +- [libunicode](https://github.com/contour-terminal/libunicode/): a + modern C++17 Unicode library +- [MariaDB](https://mariadb.org/): relational database management + system +- [Microsoft Verona](https://github.com/microsoft/verona): research + programming language for concurrent ownership +- [MongoDB](https://mongodb.com/): distributed document database +- [MongoDB Smasher](https://github.com/duckie/mongo_smasher): a small + tool to generate randomized datasets +- [OpenSpace](https://openspaceproject.com/): an open-source + astrovisualization framework +- [PenUltima Online (POL)](https://www.polserver.com/): an MMO server, + compatible with most Ultima Online clients +- [PyTorch](https://github.com/pytorch/pytorch): an open-source + machine learning library +- [quasardb](https://www.quasardb.net/): a distributed, + high-performance, associative database +- [Quill](https://github.com/odygrd/quill): asynchronous low-latency + logging library +- [QKW](https://github.com/ravijanjam/qkw): generalizing aliasing to + simplify navigation, and executing complex multi-line terminal + command sequences +- [redis-cerberus](https://github.com/HunanTV/redis-cerberus): a Redis + cluster proxy +- [redpanda](https://vectorized.io/redpanda): a 10x faster Kafka® + replacement for mission-critical systems written in C++ +- [rpclib](http://rpclib.net/): a modern C++ msgpack-RPC server and + client library +- [Salesforce Analytics + Cloud](https://www.salesforce.com/analytics-cloud/overview/): + business intelligence software +- [Scylla](https://www.scylladb.com/): a Cassandra-compatible NoSQL + data store that can handle 1 million transactions per second on a + single server +- [Seastar](http://www.seastar-project.org/): an advanced, open-source + C++ framework for high-performance server applications on modern + hardware +- [spdlog](https://github.com/gabime/spdlog): super fast C++ logging + library +- [Stellar](https://www.stellar.org/): financial platform +- [Touch Surgery](https://www.touchsurgery.com/): surgery simulator +- [TrinityCore](https://github.com/TrinityCore/TrinityCore): + open-source MMORPG framework +- [🐙 userver framework](https://userver.tech/): open-source + asynchronous framework with a rich set of abstractions and database + drivers +- [Windows Terminal](https://github.com/microsoft/terminal): the new + Windows terminal + +[More\...](https://github.com/search?q=fmtlib&type=Code) + +If you are aware of other projects using this library, please let me +know by [email](mailto:victor.zverovich@gmail.com) or by submitting an +[issue](https://github.com/fmtlib/fmt/issues). + +# 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, +\...))](https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html) in +GCC. There is a POSIX extension that adds positional arguments required +for +[i18n](https://en.wikipedia.org/wiki/Internationalization_and_localization) +to `printf` 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: + +``` c++ +std::cout << std::setprecision(2) << std::fixed << 1.23456 << "\n"; +``` + +which is a lot of typing compared to printf: + +``` c++ +printf("%.2f\n", 1.23456); +``` + +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](#benchmarks)). + +## FastFormat + +This is an interesting library that is fast, safe, and has positional +arguments. However, it has significant limitations, citing its author: + +> Three features that have no hope of being accommodated within the +> current design are: +> +> - Leading zeros (or any other non-space padding) +> - Octal/hexadecimal encoding +> - Runtime width/alignment specification + +It is also quite big and has a heavy dependency, STLSoft, which might be +too restrictive for using it 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](http://www.zverovich.net/2020/06/13/fast-int-to-string-revisited.html). + +# License + +{fmt} is distributed under the MIT +[license](https://github.com/fmtlib/fmt/blob/master/LICENSE). + +# Documentation License + +The [Format String Syntax](https://fmt.dev/latest/syntax.html) section +in the documentation is based on the one from Python [string module +documentation](https://docs.python.org/3/library/string.html#module-string). +For this reason, the documentation is distributed under the Python +Software Foundation license available in +[doc/python-license.txt](https://raw.github.com/fmtlib/fmt/master/doc/python-license.txt). +It only applies if you distribute the documentation of {fmt}. + +# Maintainers + +The {fmt} library is maintained by Victor Zverovich +([vitaut](https://github.com/vitaut)) with contributions from many other +people. See +[Contributors](https://github.com/fmtlib/fmt/graphs/contributors) and +[Releases](https://github.com/fmtlib/fmt/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](https://github.com/fmtlib/fmt/security/advisories/new). + +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. diff --git a/README.rst b/README.rst deleted file mode 100644 index 8f8657a4..00000000 --- a/README.rst +++ /dev/null @@ -1,553 +0,0 @@ -.. image:: https://user-images.githubusercontent.com/ - 576385/156254208-f5b743a9-88cf-439d-b0c0-923d53e8d551.png - :width: 25% - :alt: {fmt} - -.. image:: https://github.com/fmtlib/fmt/workflows/linux/badge.svg - :target: https://github.com/fmtlib/fmt/actions?query=workflow%3Alinux - -.. image:: https://github.com/fmtlib/fmt/workflows/macos/badge.svg - :target: https://github.com/fmtlib/fmt/actions?query=workflow%3Amacos - -.. image:: https://github.com/fmtlib/fmt/workflows/windows/badge.svg - :target: https://github.com/fmtlib/fmt/actions?query=workflow%3Awindows - -.. image:: https://oss-fuzz-build-logs.storage.googleapis.com/badges/fmt.svg - :alt: fmt is continuously fuzzed at oss-fuzz - :target: https://bugs.chromium.org/p/oss-fuzz/issues/list?\ - colspec=ID%20Type%20Component%20Status%20Proj%20Reported%20Owner%20\ - Summary&q=proj%3Dfmt&can=1 - -.. image:: https://img.shields.io/badge/stackoverflow-fmt-blue.svg - :alt: Ask questions at StackOverflow with the tag fmt - :target: https://stackoverflow.com/questions/tagged/fmt - -.. image:: https://api.securityscorecards.dev/projects/github.com/fmtlib/fmt/badge - :target: https://securityscorecards.dev/viewer/?uri=github.com/fmtlib/fmt - -**{fmt}** is an open-source formatting library providing a fast and safe -alternative to C stdio and C++ iostreams. - -If you like this project, please consider donating to one of the funds that -help victims of the war in Ukraine: https://www.stopputin.net/. - -`Documentation `__ - -`Cheat Sheets `__ - -Q&A: ask questions on `StackOverflow with the tag fmt -`_. - -Try {fmt} in `Compiler Explorer `_. - -Features --------- - -* Simple `format API `_ with positional arguments - for localization -* Implementation of `C++20 std::format - `__ and `C++23 std::print - `__ -* `Format string syntax `_ similar to Python's - `format `_ -* Fast IEEE 754 floating-point formatter with correct rounding, shortness and - round-trip guarantees using the `Dragonbox `_ - algorithm -* Portable Unicode support -* Safe `printf implementation - `_ including the POSIX - extension for positional arguments -* Extensibility: `support for user-defined types - `_ -* High performance: faster than common standard library implementations of - ``(s)printf``, iostreams, ``to_string`` and ``to_chars``, see `Speed tests`_ - and `Converting a hundred million integers to strings per second - `_ -* Small code size both in terms of source code with the minimum configuration - consisting of just three files, ``core.h``, ``format.h`` and ``format-inl.h``, - and compiled code; see `Compile time and code bloat`_ -* Reliability: the library has an extensive set of `tests - `_ and is `continuously fuzzed - `_ -* Safety: the library is fully type-safe, errors in format strings can be - reported at compile time, automatic memory management prevents buffer overflow - errors -* Ease of use: small self-contained code base, no external dependencies, - permissive MIT `license - `_ -* `Portability `_ with - consistent output across platforms and support for older compilers -* Clean warning-free codebase even on high warning levels such as - ``-Wall -Wextra -pedantic`` -* Locale independence by default -* Optional header-only configuration enabled with the ``FMT_HEADER_ONLY`` macro - -See the `documentation `_ for more details. - -Examples --------- - -**Print to stdout** (`run `_) - -.. code:: c++ - - #include - - int main() { - fmt::print("Hello, world!\n"); - } - -**Format a string** (`run `_) - -.. code:: c++ - - std::string s = fmt::format("The answer is {}.", 42); - // s == "The answer is 42." - -**Format a string using positional arguments** (`run `_) - -.. code:: c++ - - std::string s = fmt::format("I'd rather be {1} than {0}.", "right", "happy"); - // s == "I'd rather be happy than right." - -**Print chrono durations** (`run `_) - -.. code:: c++ - - #include - - 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); - } - -Output:: - - Default format: 42s 100ms - strftime-like format: 03:15:30 - -**Print a container** (`run `_) - -.. code:: c++ - - #include - #include - - int main() { - std::vector v = {1, 2, 3}; - fmt::print("{}\n", v); - } - -Output:: - - [1, 2, 3] - -**Check a format string at compile time** - -.. code:: c++ - - std::string s = fmt::format("{:d}", "I am not a number"); - -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** - -.. code:: c++ - - #include - - int main() { - auto out = fmt::output_file("guide.txt"); - out.print("Don't {}", "Panic"); - } - -This can be `5 to 9 times faster than fprintf -`_. - -**Print with colors and text styles** - -.. code:: c++ - - #include - - int main() { - fmt::print(fg(fmt::color::crimson) | fmt::emphasis::bold, - "Hello, {}!\n", "world"); - fmt::print(fg(fmt::color::floral_white) | bg(fmt::color::slate_gray) | - fmt::emphasis::underline, "Olá, {}!\n", "Mundo"); - fmt::print(fg(fmt::color::steel_blue) | fmt::emphasis::italic, - "你好{}！\n", "世界"); - } - -Output on a modern terminal with Unicode support: - -.. image:: https://github.com/fmtlib/fmt/assets/ - 576385/2a93c904-d6fa-4aa6-b453-2618e1c327d7 - -Benchmarks ----------- - -Speed tests -~~~~~~~~~~~ - -================= ============= =========== -Library Method Run Time, s -================= ============= =========== -libc printf 0.91 -libc++ std::ostream 2.49 -{fmt} 9.1 fmt::print 0.74 -Boost Format 1.80 boost::format 6.26 -Folly Format folly::format 1.87 -================= ============= =========== - -{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 with ``clang++ -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`` and ``sprintf`` on -IEEE754 ``float`` and ``double`` formatting (`dtoa-benchmark `_) -and faster than `double-conversion `_ and -`ryu `_: - -.. image:: https://user-images.githubusercontent.com/576385/ - 95684665-11719600-0ba8-11eb-8e5b-972ff4e49428.png - :target: https://fmt.dev/unknown_mac64_clang12.0.html - -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 LLVM version 8.1.0 (clang-802.0.42), -macOS Sierra, best of three) is shown in the following tables. - -**Optimized build (-O3)** - -============= =============== ==================== ================== -Method Compile Time, s Executable size, KiB Stripped size, KiB -============= =============== ==================== ================== -printf 2.6 29 26 -printf+string 16.4 29 26 -iostreams 31.1 59 55 -{fmt} 19.0 37 34 -Boost Format 91.9 226 203 -Folly Format 115.7 101 88 -============= =============== ==================== ================== - -As you can see, {fmt} has 60% less overhead in terms of resulting binary code -size compared to iostreams and comes pretty close to ``printf``. Boost Format -and Folly Format have the largest overheads. - -``printf+string`` is the same as ``printf`` but with an extra ```` -include to measure the overhead of the latter. - -**Non-optimized build** - -============= =============== ==================== ================== -Method Compile Time, s Executable size, KiB Stripped size, KiB -============= =============== ==================== ================== -printf 2.2 33 30 -printf+string 16.0 33 30 -iostreams 28.3 56 52 -{fmt} 18.2 59 50 -Boost Format 54.1 365 303 -Folly Format 79.9 445 430 -============= =============== ==================== ================== - -``libc``, ``lib(std)c++``, and ``libfmt`` 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. - -__ https://fmt.dev/latest/usage.html#building-the-library - -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:: - - $ git clone --recursive https://github.com/fmtlib/format-benchmark.git - $ cd format-benchmark - $ cmake . - -Then you can run the speed test:: - - $ make speed-test - -or the bloat test:: - - $ make bloat-test - -Migrating code --------------- - -`clang-tidy `_ v17 (not yet -released) provides the `modernize-use-std-print -`_ -check that is capable of converting occurrences of ``printf`` and -``fprintf`` to ``fmt::print`` if configured to do so. (By default it -converts to ``std::print``.) - -Projects using this library ---------------------------- - -* `0 A.D. `_: a free, open-source, cross-platform - real-time strategy game - -* `AMPL/MP `_: - an open-source library for mathematical programming - -* `Aseprite `_: - animated sprite editor & pixel art tool - -* `AvioBook `_: a comprehensive aircraft - operations suite - -* `Blizzard Battle.net `_: an online gaming platform - -* `Celestia `_: real-time 3D visualization of space - -* `Ceph `_: a scalable distributed storage system - -* `ccache `_: a compiler cache - -* `ClickHouse `_: an analytical database - management system - -* `Contour `_: a modern terminal emulator - -* `CUAUV `_: Cornell University's autonomous underwater - vehicle - -* `Drake `_: a planning, control, and analysis toolbox - for nonlinear dynamical systems (MIT) - -* `Envoy `_: C++ L7 proxy and communication bus - (Lyft) - -* `FiveM `_: a modification framework for GTA V - -* `fmtlog `_: a performant fmtlib-style - logging library with latency in nanoseconds - -* `Folly `_: Facebook open-source library - -* `GemRB `_: a portable open-source implementation of - Bioware’s Infinity Engine - -* `Grand Mountain Adventure - `_: - a beautiful open-world ski & snowboarding game - -* `HarpyWar/pvpgn `_: - Player vs Player Gaming Network with tweaks - -* `KBEngine `_: an open-source MMOG server - engine - -* `Keypirinha `_: a semantic launcher for Windows - -* `Kodi `_ (formerly xbmc): home theater software - -* `Knuth `_: high-performance Bitcoin full-node - -* `libunicode `_: a modern C++17 Unicode library - -* `MariaDB `_: relational database management system - -* `Microsoft Verona `_: - research programming language for concurrent ownership - -* `MongoDB `_: distributed document database - -* `MongoDB Smasher `_: a small tool to - generate randomized datasets - -* `OpenSpace `_: an open-source - astrovisualization framework - -* `PenUltima Online (POL) `_: - an MMO server, compatible with most Ultima Online clients - -* `PyTorch `_: an open-source machine - learning library - -* `quasardb `_: a distributed, high-performance, - associative database - -* `Quill `_: asynchronous low-latency logging library - -* `QKW `_: generalizing aliasing to simplify - navigation, and executing complex multi-line terminal command sequences - -* `redis-cerberus `_: a Redis cluster - proxy - -* `redpanda `_: a 10x faster Kafka® replacement - for mission-critical systems written in C++ - -* `rpclib `_: a modern C++ msgpack-RPC server and client - library - -* `Salesforce Analytics Cloud - `_: - business intelligence software - -* `Scylla `_: a Cassandra-compatible NoSQL data store - that can handle 1 million transactions per second on a single server - -* `Seastar `_: an advanced, open-source C++ - framework for high-performance server applications on modern hardware - -* `spdlog `_: super fast C++ logging library - -* `Stellar `_: financial platform - -* `Touch Surgery `_: surgery simulator - -* `TrinityCore `_: open-source - MMORPG framework - -* `🐙 userver framework `_: open-source asynchronous - framework with a rich set of abstractions and database drivers - -* `Windows Terminal `_: the new Windows - terminal - -`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 `_ -to ``printf`` 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: - -.. code:: c++ - - std::cout << std::setprecision(2) << std::fixed << 1.23456 << "\n"; - -which is a lot of typing compared to printf: - -.. code:: c++ - - printf("%.2f\n", 1.23456); - -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: - - Three features that have no hope of being accommodated within the - current design are: - - * Leading zeros (or any other non-space padding) - * Octal/hexadecimal encoding - * Runtime width/alignment specification - -It is also quite big and has a heavy dependency, STLSoft, which might be too -restrictive for using it 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.