README.rst - platform/external/fmtlib - Git at Google

 {fmt}
 =====

 .. image:: https://travis-ci.org/fmtlib/fmt.png?branch=master
    :target: https://travis-ci.org/fmtlib/fmt

 .. image:: https://ci.appveyor.com/api/projects/status/ehjkiefde6gucy1v
    :target: https://ci.appveyor.com/project/vitaut/fmt

 .. image:: https://img.shields.io/badge/stackoverflow-fmt-blue.svg
    :alt: Ask questions at StackOverflow with the tag fmt
    :target: http://stackoverflow.com/questions/tagged/fmt

 .. image:: https://oss-fuzz-build-logs.storage.googleapis.com/badges/libfmt.svg
    :alt: fmt is continuously fuzzed att oss-fuzz
    :target: https://bugs.chromium.org/p/oss-fuzz/issues/list?colspec=ID%20Type%20Component%20Status%20Proj%20Reported%20Owner%20Summary&q=proj%3Dfmt&can=1

 **{fmt}** is an open-source formatting library for C++.
 It can be used as a safe and fast alternative to (s)printf and iostreams.

 `Documentation <https://fmt.dev/latest/>`__

 Q&A: ask questions on `StackOverflow with the tag fmt <http://stackoverflow.com/questions/tagged/fmt>`_.

 Features
 --------

 * Replacement-based `format API <https://fmt.dev/dev/api.html>`_ with
   positional arguments for localization.
 * `Format string syntax <https://fmt.dev/dev/syntax.html>`_ similar to the one
   of `str.format <https://docs.python.org/3/library/stdtypes.html#str.format>`_
   in Python.
 * Safe `printf implementation
   <https://fmt.dev/latest/api.html#printf-formatting>`_ including
   the POSIX extension for positional arguments.
 * Implementation of `C++20 std::format <https://fmt.dev/Text%20Formatting.html>`__.
 * Support for user-defined types.
 * High performance: faster than common standard library implementations of
   `printf <http://en.cppreference.com/w/cpp/io/c/fprintf>`_ and
   iostreams. See `Speed tests`_ and `Fast integer to string conversion in C++
   <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
 * Small code size both in terms of source code (the minimum configuration
   consists of just three header 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 `unit tests
   <https://github.com/fmtlib/fmt/tree/master/test>`_ 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
   <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
   (``-Wall -Wextra -pedantic``).
 * Support for wide strings.
 * Optional header-only configuration enabled with the ``FMT_HEADER_ONLY`` macro.

 See the `documentation <https://fmt.dev/latest/>`_ for more details.

 Examples
 --------

 Print ``Hello, world!`` to ``stdout``:

 .. code:: c++

     fmt::print("Hello, {}!", "world");  // Python-like format string syntax
     fmt::printf("Hello, %s!", "world"); // printf format string syntax

 Format a string and use positional arguments:

 .. code:: c++

     std::string s = fmt::format("I'd rather be {1} than {0}.", "right", "happy");
     // s == "I'd rather be happy than right."

 Check a format string at compile time:

 .. code:: c++

     // test.cc
     #define FMT_STRING_ALIAS 1
     #include <fmt/format.h>
     std::string s = format(fmt("{2}"), 42);

 .. code::

     $ c++ -Iinclude -std=c++14 test.cc
     ...
     test.cc:4:17: note: in instantiation of function template specialization 'fmt::v5::format<S, int>' requested here
     std::string s = format(fmt("{2}"), 42);
                     ^
     include/fmt/core.h:778:19: note: non-constexpr function 'on_error' cannot be used in a constant expression
         ErrorHandler::on_error(message);
                       ^
     include/fmt/format.h:2226:16: note: in call to '&checker.context_->on_error(&"argument index out of range"[0])'
           context_.on_error("argument index out of range");
                    ^

 Use {fmt} as a safe portable replacement for ``itoa``
 (`godbolt <https://godbolt.org/g/NXmpU4>`_):

 .. code:: c++

     fmt::memory_buffer buf;
     format_to(buf, "{}", 42);    // replaces itoa(42, buffer, 10)
     format_to(buf, "{:x}", 42);  // replaces itoa(42, buffer, 16)
     // access the string with to_string(buf) or buf.data()

 Format objects of user-defined types via a simple `extension API
 <https://fmt.dev/latest/api.html#formatting-user-defined-types>`_:

 .. code:: c++

     #include "fmt/format.h"

     struct date {
       int year, month, day;
     };

     template <>
     struct fmt::formatter<date> {
       template <typename ParseContext>
       constexpr auto parse(ParseContext &ctx) { return ctx.begin(); }

       template <typename FormatContext>
       auto format(const date &d, FormatContext &ctx) {
         return format_to(ctx.out(), "{}-{}-{}", 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"

 Create your own functions similar to `format
 <https://fmt.dev/latest/api.html#format>`_ and
 `print <https://fmt.dev/latest/api.html#print>`_
 which take arbitrary arguments (`godbolt <https://godbolt.org/g/MHjHVf>`_):

 .. code:: c++

     // 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...));
     }

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

 Note that ``vreport_error`` is not parameterized on argument types which can
 improve compile times and reduce code size compared to a fully parameterized
 version.

 Benchmarks
 ----------

 Speed tests
 ~~~~~~~~~~~

 ================= ============= ===========
 Library           Method        Run Time, s
 ================= ============= ===========
 libc              printf          1.01
 libc++            std::ostream    3.04
 {fmt} 1632f72     fmt::print      0.86
 tinyformat 2.0.1  tfm::printf     3.23
 Boost Format 1.67 boost::format   7.98
 Folly Format      folly::format   2.23
 ================= ============= ===========

 {fmt} is the fastest of the benchmarked methods, ~17% faster than ``printf``.

 The above results were generated by building ``tinyformat_test.cpp`` on macOS
 10.14.3 with ``clang++ -O3 -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/tinyformat_test.cpp>`_.

 {fmt} is 10x faster than ``std::ostringstream`` and ``sprintf`` on floating-point
 formatting (`dtoa-benchmark <https://github.com/fmtlib/dtoa-benchmark>`_)
 and as fast as `double-conversion <https://github.com/google/double-conversion>`_:

 .. image:: https://user-images.githubusercontent.com/576385/54883977-9fe8c000-4e28-11e9-8bde-272d122e7c52.jpg
    :target: https://fmt.dev/unknown_mac64_clang10.0.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
 tinyformat               44.0                  103                 97
 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 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
 tinyformat               32.6                   88                 82
 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 and tinyformat are
 header-only libraries so they don't provide any linkage options.

 Running the tests
 ~~~~~~~~~~~~~~~~~

 Please refer to `Building the library`__ for the 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

 Projects using this library
 ---------------------------

 * `0 A.D. <http://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

 * `AvioBook <https://www.aviobook.aero/en>`_: A comprehensive aircraft
   operations suite

 * `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

 * `CUAUV <http://cuauv.org/>`_: Cornell University's autonomous underwater
   vehicle

 * `HarpyWar/pvpgn <https://github.com/pvpgn/pvpgn-server>`_:
   Player vs Player Gaming Network with tweaks

 * `KBEngine <http://kbengine.org/>`_: An open-source MMOG server engine

 * `Keypirinha <http://keypirinha.com/>`_: A semantic launcher for Windows

 * `Kodi <https://kodi.tv/>`_ (formerly xbmc): Home theater software

 * `Lifeline <https://github.com/peter-clark/lifeline>`_: A 2D game

 * `Drake <http://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

 * `MongoDB <https://mongodb.com/>`_: Distributed document database

 * `MongoDB Smasher <https://github.com/duckie/mongo_smasher>`_: A small tool to
   generate randomized datasets

 * `OpenSpace <http://openspaceproject.com/>`_: An open-source astrovisualization
   framework

 * `PenUltima Online (POL) <http://www.polserver.com/>`_:
   An MMO server, compatible with most Ultima Online clients

 * `quasardb <https://www.quasardb.net/>`_: A distributed, high-performance,
   associative database

 * `readpe <https://bitbucket.org/sys_dev/readpe>`_: Read Portable Executable

 * `redis-cerberus <https://github.com/HunanTV/redis-cerberus>`_: A Redis cluster
   proxy

 * `rpclib <http://rpclib.net/>`_: A modern C++ msgpack-RPC server and client
   library

 * `Saddy <https://github.com/mamontov-cpp/saddy-graphics-engine-2d>`_:
   Small crossplatform 2D graphic engine

 * `Salesforce Analytics Cloud <http://www.salesforce.com/analytics-cloud/overview/>`_:
   Business intelligence software

 * `Scylla <http://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

 `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, ...))
 <http://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 which 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 which 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.

 Loki SafeFormat
 ~~~~~~~~~~~~~~~

 SafeFormat is a formatting library which uses ``printf``-like format strings and
 is type safe. It doesn't support user-defined types or positional arguments and
 makes unconventional use of ``operator()`` for passing format arguments.

 Tinyformat
 ~~~~~~~~~~

 This library supports ``printf``-like format strings and is very small .
 It doesn't support positional arguments and wrapping it in C++98 is somewhat
 difficult. Tinyformat relies on iostreams which limits its performance.

 Boost Spirit.Karma
 ~~~~~~~~~~~~~~~~~~

 This is not really 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_int`` on Karma's own benchmark,
 see `Fast integer to string conversion in C++
 <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.

 FAQ
 ---

 Q: how can I capture formatting arguments and format them later?

 A: use ``std::tuple``:

 .. code:: c++

    template <typename... Args>
    auto capture(const Args&... args) {
      return std::make_tuple(args...);
    }

    auto print_message = [](const auto&... args) {
      fmt::print(args...);
    };

    // Capture and store arguments:
    auto args = capture("{} {}", 42, "foo");
    // Do formatting:
    std::apply(print_message, args);

 License
 -------

 {fmt} is distributed under the MIT `license
 <https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_.

 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>`_
 adapted for the current library. 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.

 Acknowledgments
 ---------------

 The {fmt} library is maintained by Victor Zverovich (`vitaut
 <https://github.com/vitaut>`_) and Jonathan Müller (`foonathan
 <https://github.com/foonathan>`_) 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.

 The benchmark section of this readme file and the performance tests are taken
 from the excellent `tinyformat <https://github.com/c42f/tinyformat>`_ library
 written by Chris Foster.  Boost Format library is acknowledged transitively
 since it had some influence on tinyformat.
 Some ideas used in the implementation are borrowed from `Loki
 <http://loki-lib.sourceforge.net/>`_ SafeFormat and `Diagnostic API
 <http://clang.llvm.org/doxygen/classclang_1_1Diagnostic.html>`_ in
 `Clang <http://clang.llvm.org/>`_.
 Format string syntax and the documentation are based on Python's `str.format
 <https://docs.python.org/3/library/stdtypes.html#str.format>`_.
 Thanks `Doug Turnbull <https://github.com/softwaredoug>`_ for his valuable
 comments and contribution to the design of the type-safe API and
 `Gregory Czajkowski <https://github.com/gcflymoto>`_ for implementing binary
 formatting. Thanks `Ruslan Baratov <https://github.com/ruslo>`_ for comprehensive
 `comparison of integer formatting algorithms <https://github.com/ruslo/int-dec-format-tests>`_
 and useful comments regarding performance, `Boris Kaul <https://github.com/localvoid>`_ for
 `C++ counting digits benchmark <https://github.com/localvoid/cxx-benchmark-count-digits>`_.
 Thanks to `CarterLi <https://github.com/CarterLi>`_ for contributing various
 improvements to the code.
	{fmt}
	=====

	.. image:: https://travis-ci.org/fmtlib/fmt.png?branch=master
	:target: https://travis-ci.org/fmtlib/fmt

	.. image:: https://ci.appveyor.com/api/projects/status/ehjkiefde6gucy1v
	:target: https://ci.appveyor.com/project/vitaut/fmt

	.. image:: https://img.shields.io/badge/stackoverflow-fmt-blue.svg
	:alt: Ask questions at StackOverflow with the tag fmt
	:target: http://stackoverflow.com/questions/tagged/fmt

	.. image:: https://oss-fuzz-build-logs.storage.googleapis.com/badges/libfmt.svg
	:alt: fmt is continuously fuzzed att oss-fuzz
	:target: https://bugs.chromium.org/p/oss-fuzz/issues/list?colspec=ID%20Type%20Component%20Status%20Proj%20Reported%20Owner%20Summary&q=proj%3Dfmt&can=1

	{fmt} is an open-source formatting library for C++.
	It can be used as a safe and fast alternative to (s)printf and iostreams.

	`Documentation <https://fmt.dev/latest/>`__

	Q&A: ask questions on `StackOverflow with the tag fmt <http://stackoverflow.com/questions/tagged/fmt>`_.

	Features
	--------

	* Replacement-based `format API <https://fmt.dev/dev/api.html>`_ with
	positional arguments for localization.
	* `Format string syntax <https://fmt.dev/dev/syntax.html>`_ similar to the one
	of `str.format <https://docs.python.org/3/library/stdtypes.html#str.format>`_
	in Python.
	* Safe `printf implementation
	<https://fmt.dev/latest/api.html#printf-formatting>`_ including
	the POSIX extension for positional arguments.
	* Implementation of `C++20 std::format <https://fmt.dev/Text%20Formatting.html>`__.
	* Support for user-defined types.
	* High performance: faster than common standard library implementations of
	`printf <http://en.cppreference.com/w/cpp/io/c/fprintf>`_ and
	iostreams. See `Speed tests`_ and `Fast integer to string conversion in C++
	<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
	* Small code size both in terms of source code (the minimum configuration
	consists of just three header 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 `unit tests
	<https://github.com/fmtlib/fmt/tree/master/test>`_ 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
	<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
	(``-Wall -Wextra -pedantic``).
	* Support for wide strings.
	* Optional header-only configuration enabled with the ``FMT_HEADER_ONLY`` macro.

	See the `documentation <https://fmt.dev/latest/>`_ for more details.

	Examples
	--------

	Print ``Hello, world!`` to ``stdout``:

	.. code:: c++

	fmt::print("Hello, {}!", "world"); // Python-like format string syntax
	fmt::printf("Hello, %s!", "world"); // printf format string syntax

	Format a string and use positional arguments:

	.. code:: c++

	std::string s = fmt::format("I'd rather be {1} than {0}.", "right", "happy");
	// s == "I'd rather be happy than right."

	Check a format string at compile time:

	.. code:: c++

	// test.cc
	#define FMT_STRING_ALIAS 1
	#include <fmt/format.h>
	std::string s = format(fmt("{2}"), 42);

	.. code::

	$ c++ -Iinclude -std=c++14 test.cc
	...
	test.cc:4:17: note: in instantiation of function template specialization 'fmt::v5::format<S, int>' requested here
	std::string s = format(fmt("{2}"), 42);
	^
	include/fmt/core.h:778:19: note: non-constexpr function 'on_error' cannot be used in a constant expression
	ErrorHandler::on_error(message);
	^
	include/fmt/format.h:2226:16: note: in call to '&checker.context_->on_error(&"argument index out of range"[0])'
	context_.on_error("argument index out of range");
	^

	Use {fmt} as a safe portable replacement for ``itoa``
	(`godbolt <https://godbolt.org/g/NXmpU4>`_):

	.. code:: c++

	fmt::memory_buffer buf;
	format_to(buf, "{}", 42); // replaces itoa(42, buffer, 10)
	format_to(buf, "{:x}", 42); // replaces itoa(42, buffer, 16)
	// access the string with to_string(buf) or buf.data()

	Format objects of user-defined types via a simple `extension API
	<https://fmt.dev/latest/api.html#formatting-user-defined-types>`_:

	.. code:: c++

	#include "fmt/format.h"

	struct date {
	int year, month, day;
	};

	template <>
	struct fmt::formatter<date> {
	template <typename ParseContext>
	constexpr auto parse(ParseContext &ctx) { return ctx.begin(); }

	template <typename FormatContext>
	auto format(const date &d, FormatContext &ctx) {
	return format_to(ctx.out(), "{}-{}-{}", 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"

	Create your own functions similar to `format
	<https://fmt.dev/latest/api.html#format>`_ and
	`print <https://fmt.dev/latest/api.html#print>`_
	which take arbitrary arguments (`godbolt <https://godbolt.org/g/MHjHVf>`_):

	.. code:: c++

	// 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...));
	}

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

	Note that ``vreport_error`` is not parameterized on argument types which can
	improve compile times and reduce code size compared to a fully parameterized
	version.

	Benchmarks
	----------

	Speed tests
	~~~~~~~~~~~

	================= ============= ===========
	Library Method Run Time, s
	================= ============= ===========
	libc printf 1.01
	libc++ std::ostream 3.04
	{fmt} 1632f72 fmt::print 0.86
	tinyformat 2.0.1 tfm::printf 3.23
	Boost Format 1.67 boost::format 7.98
	Folly Format folly::format 2.23
	================= ============= ===========

	{fmt} is the fastest of the benchmarked methods, ~17% faster than ``printf``.

	The above results were generated by building ``tinyformat_test.cpp`` on macOS
	10.14.3 with ``clang++ -O3 -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/tinyformat_test.cpp>`_.

	{fmt} is 10x faster than ``std::ostringstream`` and ``sprintf`` on floating-point
	formatting (`dtoa-benchmark <https://github.com/fmtlib/dtoa-benchmark>`_)
	and as fast as `double-conversion <https://github.com/google/double-conversion>`_:

	.. image:: https://user-images.githubusercontent.com/576385/54883977-9fe8c000-4e28-11e9-8bde-272d122e7c52.jpg
	:target: https://fmt.dev/unknown_mac64_clang10.0.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
	tinyformat 44.0 103 97
	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 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
	tinyformat 32.6 88 82
	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 and tinyformat are
	header-only libraries so they don't provide any linkage options.

	Running the tests
	~~~~~~~~~~~~~~~~~

	Please refer to `Building the library`__ for the 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

	Projects using this library
	---------------------------

	* `0 A.D. <http://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

	* `AvioBook <https://www.aviobook.aero/en>`_: A comprehensive aircraft
	operations suite

	* `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

	* `CUAUV <http://cuauv.org/>`_: Cornell University's autonomous underwater
	vehicle

	* `HarpyWar/pvpgn <https://github.com/pvpgn/pvpgn-server>`_:
	Player vs Player Gaming Network with tweaks

	* `KBEngine <http://kbengine.org/>`_: An open-source MMOG server engine

	* `Keypirinha <http://keypirinha.com/>`_: A semantic launcher for Windows

	* `Kodi <https://kodi.tv/>`_ (formerly xbmc): Home theater software

	* `Lifeline <https://github.com/peter-clark/lifeline>`_: A 2D game

	* `Drake <http://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

	* `MongoDB <https://mongodb.com/>`_: Distributed document database

	* `MongoDB Smasher <https://github.com/duckie/mongo_smasher>`_: A small tool to
	generate randomized datasets

	* `OpenSpace <http://openspaceproject.com/>`_: An open-source astrovisualization
	framework

	* `PenUltima Online (POL) <http://www.polserver.com/>`_:
	An MMO server, compatible with most Ultima Online clients

	* `quasardb <https://www.quasardb.net/>`_: A distributed, high-performance,
	associative database

	* `readpe <https://bitbucket.org/sys_dev/readpe>`_: Read Portable Executable

	* `redis-cerberus <https://github.com/HunanTV/redis-cerberus>`_: A Redis cluster
	proxy

	* `rpclib <http://rpclib.net/>`_: A modern C++ msgpack-RPC server and client
	library

	* `Saddy <https://github.com/mamontov-cpp/saddy-graphics-engine-2d>`_:
	Small crossplatform 2D graphic engine

	* `Salesforce Analytics Cloud <http://www.salesforce.com/analytics-cloud/overview/>`_:
	Business intelligence software

	* `Scylla <http://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

	`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, ...))
	<http://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 which 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 which 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.

	Loki SafeFormat
	~~~~~~~~~~~~~~~

	SafeFormat is a formatting library which uses ``printf``-like format strings and
	is type safe. It doesn't support user-defined types or positional arguments and
	makes unconventional use of ``operator()`` for passing format arguments.

	Tinyformat
	~~~~~~~~~~

	This library supports ``printf``-like format strings and is very small .
	It doesn't support positional arguments and wrapping it in C++98 is somewhat
	difficult. Tinyformat relies on iostreams which limits its performance.

	Boost Spirit.Karma
	~~~~~~~~~~~~~~~~~~

	This is not really 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_int`` on Karma's own benchmark,
	see `Fast integer to string conversion in C++
	<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.

	FAQ
	---

	Q: how can I capture formatting arguments and format them later?

	A: use ``std::tuple``:

	.. code:: c++

	template <typename... Args>
	auto capture(const Args&... args) {
	return std::make_tuple(args...);
	}

	auto print_message = [](const auto&... args) {
	fmt::print(args...);
	};

	// Capture and store arguments:
	auto args = capture("{} {}", 42, "foo");
	// Do formatting:
	std::apply(print_message, args);

	License
	-------

	{fmt} is distributed under the MIT `license
	<https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_.

	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>`_
	adapted for the current library. 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.

	Acknowledgments
	---------------

	The {fmt} library is maintained by Victor Zverovich (`vitaut
	<https://github.com/vitaut>`_) and Jonathan Müller (`foonathan
	<https://github.com/foonathan>`_) 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.

	The benchmark section of this readme file and the performance tests are taken
	from the excellent `tinyformat <https://github.com/c42f/tinyformat>`_ library
	written by Chris Foster. Boost Format library is acknowledged transitively
	since it had some influence on tinyformat.
	Some ideas used in the implementation are borrowed from `Loki
	<http://loki-lib.sourceforge.net/>`_ SafeFormat and `Diagnostic API
	<http://clang.llvm.org/doxygen/classclang_1_1Diagnostic.html>`_ in
	`Clang <http://clang.llvm.org/>`_.
	Format string syntax and the documentation are based on Python's `str.format
	<https://docs.python.org/3/library/stdtypes.html#str.format>`_.
	Thanks `Doug Turnbull <https://github.com/softwaredoug>`_ for his valuable
	comments and contribution to the design of the type-safe API and
	`Gregory Czajkowski <https://github.com/gcflymoto>`_ for implementing binary
	formatting. Thanks `Ruslan Baratov <https://github.com/ruslo>`_ for comprehensive
	`comparison of integer formatting algorithms <https://github.com/ruslo/int-dec-format-tests>`_
	and useful comments regarding performance, `Boris Kaul <https://github.com/localvoid>`_ for
	`C++ counting digits benchmark <https://github.com/localvoid/cxx-benchmark-count-digits>`_.
	Thanks to `CarterLi <https://github.com/CarterLi>`_ for contributing various
	improvements to the code.