diff options
Diffstat (limited to 'src/seastar/fmt/README.rst')
| -rw-r--r-- | src/seastar/fmt/README.rst | 519 |
1 files changed, 519 insertions, 0 deletions
diff --git a/src/seastar/fmt/README.rst b/src/seastar/fmt/README.rst new file mode 100644 index 00000000..3e43b308 --- /dev/null +++ b/src/seastar/fmt/README.rst @@ -0,0 +1,519 @@ +{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://badges.gitter.im/Join%20Chat.svg + :alt: Join the chat at https://gitter.im/fmtlib/fmt + :target: https://gitter.im/fmtlib/fmt + +**{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 <http://fmtlib.net/latest/>`__ + +This is a development branch that implements the C++ standards proposal `P0645 +Text Formatting <http://fmtlib.net/Text%20Formatting.html>`__. +Released versions are available from the `Releases page +<https://github.com/fmtlib/fmt/releases>`__. + +Features +-------- + +* Replacement-based `format API <http://fmtlib.net/dev/api.html>`_ with + positional arguments for localization. +* `Format string syntax <http://fmtlib.net/dev/syntax.html>`_ similar to the one + of `str.format <https://docs.python.org/2/library/stdtypes.html#str.format>`_ + in Python. +* Safe `printf implementation + <http://fmtlib.net/latest/api.html#printf-formatting>`_ including + the POSIX extension for positional arguments. +* Support for user-defined types. +* High speed: performance of the format API is close to that of glibc's `printf + <http://en.cppreference.com/w/cpp/io/c/fprintf>`_ and better than the + performance of 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>`_. +* 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 BSD `license + <https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_ +* `Portability <http://fmtlib.net/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 <http://fmtlib.net/latest/>`_ for more details. + +Examples +-------- + +This prints ``Hello, world!`` to stdout: + +.. code:: c++ + + fmt::print("Hello, {}!", "world"); // uses Python-like format string syntax + fmt::printf("Hello, %s!", "world"); // uses printf format string syntax + +Arguments can be accessed by position and arguments' indices can be repeated: + +.. code:: c++ + + std::string s = fmt::format("{0}{1}{0}", "abra", "cad"); + // s == "abracadabra" + +Format strings can be checked 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"); + ^ + +{fmt} can be used 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 using to_string(buf) or buf.data() + +Formatting of user-defined types is supported via a simple +`extension API <http://fmtlib.net/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" + +You can create your own functions similar to `format +<http://fmtlib.net/latest/api.html#format>`_ and +`print <http://fmtlib.net/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 fully parameterized +version. + +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 + +* `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 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=cppformat&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 library and +FastFormat. 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 mostly solved 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, referred to this situation with +IOStreams as "chevron hell". IOStreams doesn't support positional arguments +by design. + +The good part is that IOStreams supports user-defined types and is safe +although error reporting is awkward. + +Boost Format library +~~~~~~~~~~~~~~~~~~~~ + +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. It makes unconventional use of ``operator()`` for passing +format arguments. + +Tinyformat +~~~~~~~~~~ + +This library supports printf-like format strings and is very small and +fast. Unfortunately it doesn't support positional arguments and wrapping +it in C++98 is somewhat difficult. Also its performance and code compactness +are limited by IOStreams. + +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::Writer`` 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>`_. + +Benchmarks +---------- + +Speed tests +~~~~~~~~~~~ + +The following speed tests results were generated by building +``tinyformat_test.cpp`` on Ubuntu GNU/Linux 14.04.1 with +``g++-4.8.2 -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 2000000 times with output sent to ``/dev/null``; for +further details see the `source +<https://github.com/fmtlib/format-benchmark/blob/master/tinyformat_test.cpp>`_. + +================= ============= =========== +Library Method Run Time, s +================= ============= =========== +libc printf 1.35 +libc++ std::ostream 3.42 +fmt 534bff7 fmt::print 1.56 +tinyformat 2.0.1 tfm::printf 3.73 +Boost Format 1.54 boost::format 8.44 +Folly Format folly::format 2.54 +================= ============= =========== + +As you can see ``boost::format`` is much slower than the alternative methods; this +is confirmed by `other tests <http://accu.org/index.php/journals/1539>`_. +Tinyformat is quite good coming close to IOStreams. Unfortunately tinyformat +cannot be faster than the IOStreams because it uses them internally. +Performance of fmt is close to that of printf, being `faster than printf on integer +formatting <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_, +but slower on floating-point formatting which dominates this benchmark. + +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. + +__ http://fmtlib.net/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 + +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 BSD `license +<https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_. + +The `Format String Syntax +<http://fmtlib.net/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 +<http://docs.python.org/2/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. |