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Victor Zverovich
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@ -57,21 +57,14 @@ See the `documentation <http://fmtlib.net/latest/>`_ for more details.
Examples Examples
-------- --------
This prints ``Hello, world!`` to stdout: Print ``Hello, world!`` to ``stdout``:
.. code:: c++ .. code:: c++
fmt::print("Hello, {}!", "world"); // uses Python-like format string syntax fmt::print("Hello, {}!", "world"); // uses Python-like format string syntax
fmt::printf("Hello, %s!", "world"); // uses printf 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: Check a format string at compile time:
.. code:: c++
std::string s = fmt::format("{0}{1}{0}", "abra", "cad");
// s == "abracadabra"
Format strings can be checked at compile time:
.. code:: c++ .. code:: c++
@ -94,7 +87,7 @@ Format strings can be checked at compile time:
context_.on_error("argument index out of range"); context_.on_error("argument index out of range");
^ ^
{fmt} can be used as a safe portable replacement for ``itoa`` Use {fmt} as a safe portable replacement for ``itoa``
(`godbolt <https://godbolt.org/g/NXmpU4>`_): (`godbolt <https://godbolt.org/g/NXmpU4>`_):
.. code:: c++ .. code:: c++
@ -129,7 +122,7 @@ Formatting of user-defined types is supported via a simple
std::string s = fmt::format("The date is {}", date{2012, 12, 9}); std::string s = fmt::format("The date is {}", date{2012, 12, 9});
// s == "The date is 2012-12-9" // s == "The date is 2012-12-9"
You can create your own functions similar to `format Create your own functions similar to `format
<http://fmtlib.net/latest/api.html#format>`_ and <http://fmtlib.net/latest/api.html#format>`_ and
`print <http://fmtlib.net/latest/api.html#print>`_ `print <http://fmtlib.net/latest/api.html#print>`_
which take arbitrary arguments (`godbolt <https://godbolt.org/g/MHjHVf>`_): which take arbitrary arguments (`godbolt <https://godbolt.org/g/MHjHVf>`_):
@ -152,6 +145,108 @@ Note that ``vreport_error`` is not parameterized on argument types which can
improve compile times and reduce code size compared to fully parameterized improve compile times and reduce code size compared to fully parameterized
version. 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>`_.
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
Projects using this library Projects using this library
--------------------------- ---------------------------
@ -331,108 +426,6 @@ than ``fmt::format_int`` on Karma's own benchmark,
see `Fast integer to string conversion in C++ see `Fast integer to string conversion in C++
<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_. <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
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>`_.
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 FAQ
--- ---
@ -459,7 +452,7 @@ A: use ``std::tuple``:
License License
------- -------
fmt is distributed under the BSD `license {fmt} is distributed under the BSD `license
<https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_. <https://github.com/fmtlib/fmt/blob/master/LICENSE.rst>`_.
The `Format String Syntax The `Format String Syntax
@ -475,7 +468,7 @@ It only applies if you distribute the documentation of fmt.
Acknowledgments Acknowledgments
--------------- ---------------
The fmt library is maintained by Victor Zverovich (`vitaut The {fmt} library is maintained by Victor Zverovich (`vitaut
<https://github.com/vitaut>`_) and Jonathan Müller (`foonathan <https://github.com/vitaut>`_) and Jonathan Müller (`foonathan
<https://github.com/foonathan>`_) with contributions from many other people. <https://github.com/foonathan>`_) with contributions from many other people.
See `Contributors <https://github.com/fmtlib/fmt/graphs/contributors>`_ and See `Contributors <https://github.com/fmtlib/fmt/graphs/contributors>`_ and