duckstation

README.rst (20274B)

---

 .. image:: https://user-images.githubusercontent.com/
            576385/156254208-f5b743a9-88cf-439d-b0c0-923d53e8d551.png
    :width: 25%
    :alt: {fmt}
 
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    :target: https://github.com/fmtlib/fmt/actions?query=workflow%3Alinux
 
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    :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
 
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    :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 <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>`__
 * `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`_
   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`_
 * 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%20
   Component%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>`_)
 
 .. code:: c++
 
     #include <fmt/core.h>
     
     int main() {
       fmt::print("Hello, world!\n");
     }
 
 **Format a string** (`run <https://godbolt.org/z/oK8h33>`_)
 
 .. code:: 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>`_)
 
 .. 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 <https://godbolt.org/z/K8s4Mc>`_)
 
 .. code:: c++
 
     #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);
     }
 
 Output::
 
     Default format: 42s 100ms
     strftime-like format: 03:15:30
 
 **Print a container** (`run <https://godbolt.org/z/MxM1YqjE7>`_)
 
 .. code:: c++
 
     #include <vector>
     #include <fmt/ranges.h>
 
     int main() {
       std::vector<int> 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 <fmt/os.h>
 
     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**
 
 .. code:: c++
 
     #include <fmt/color.h>
 
     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, "Hello, {}!\n", "мир");
       fmt::print(fg(fmt::color::steel_blue) | fmt::emphasis::italic,
                  "Hello, {}!\n", "世界");
     }
 
 Output on a modern terminal:
 
 .. image:: https://user-images.githubusercontent.com/
            576385/88485597-d312f600-cf2b-11ea-9cbe-61f535a86e28.png
 
 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/
            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
 <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 ``<string>``
 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 <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:
 
 .. 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
 <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.rst>`_.
 
 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.