mirror of
https://github.com/fmtlib/fmt.git
synced 2024-12-02 14:30:10 +00:00
156 lines
4.6 KiB
ReStructuredText
156 lines
4.6 KiB
ReStructuredText
Overview
|
|
========
|
|
|
|
C++ Format (cppformat) is an open-source formatting library for C++.
|
|
It can be used as a safe alternative to printf or as a fast
|
|
alternative to IOStreams.
|
|
|
|
.. _format-api:
|
|
|
|
Format API
|
|
----------
|
|
|
|
The replacement-based Format API provides a safe alternative to ``printf``,
|
|
``sprintf`` and friends with comparable or `better performance
|
|
<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
|
|
The `format string syntax <doc/latest/index.html#format-string-syntax>`_ is similar
|
|
to the one used by `str.format <http://docs.python.org/2/library/stdtypes.html#str.format>`_
|
|
in Python:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::format("The answer is {}", 42);
|
|
|
|
The ``fmt::format`` function returns a string "The answer is 42". You can use
|
|
``fmt::MemoryWriter`` to avoid constructing ``std::string``:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::MemoryWriter w;
|
|
w.write("Look, a {} string", 'C');
|
|
w.c_str(); // returns a C string (const char*)
|
|
|
|
The ``fmt::print`` function performs formatting and writes the result to a file:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::print(stderr, "System error code = {}\n", errno);
|
|
|
|
The file argument can be omitted in which case the function prints to
|
|
``stdout``:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::print("Don't {}\n", "panic");
|
|
|
|
If your compiler supports C++11, then the formatting functions are implemented
|
|
with variadic templates. Otherwise variadic functions are emulated by generating
|
|
a set of lightweight wrappers. This ensures compatibility with older compilers
|
|
while providing a natural API.
|
|
|
|
The Format API also supports positional arguments useful for localization:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::print("I'd rather be {1} than {0}.", "right", "happy");
|
|
|
|
.. _write-api:
|
|
|
|
Write API
|
|
---------
|
|
|
|
The concatenation-based Write API (experimental) provides a
|
|
`fast <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_
|
|
stateless alternative to IOStreams:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::MemoryWriter out;
|
|
out << "The answer in hexadecimal is " << hex(42);
|
|
|
|
.. _safety:
|
|
|
|
Safety
|
|
------
|
|
|
|
The library is fully type safe, automatic memory management prevents buffer overflow,
|
|
errors in format strings are reported using exceptions. For example, the code
|
|
|
|
.. code:: c++
|
|
|
|
fmt::format("The answer is {:d}", "forty-two");
|
|
|
|
throws a ``FormatError`` exception with description
|
|
"unknown format code 'd' for string", because the argument
|
|
``"forty-two"`` is a string while the format code ``d``
|
|
only applies to integers.
|
|
|
|
Where possible, errors are catched at compile time. For example, the code
|
|
|
|
.. code:: c++
|
|
|
|
fmt::format("Cyrillic letter {}", L'\x42e');
|
|
|
|
produces a compile-time error because wide character ``L'\x42e'`` cannot be
|
|
formatted into a narrow string. You can use a wide format string instead:
|
|
|
|
.. code:: c++
|
|
|
|
fmt::format(L"Cyrillic letter {}", L'\x42e');
|
|
|
|
For comparison, writing a wide character to ``std::ostream`` results in
|
|
its numeric value being written to the stream (i.e. 1070 instead of letter 'ю' which
|
|
is represented by ``L'\x42e'`` if we use Unicode) which is rarely what is needed.
|
|
|
|
.. _portability:
|
|
|
|
Portability
|
|
-----------
|
|
|
|
C++ Format is highly portable. Here is an incomplete list of operating systems and
|
|
compilers where it has been tested and known to work:
|
|
|
|
* 64-bit (amd64) GNU/Linux with GCC 4.4.3, `4.6.3 <https://travis-ci.org/cppformat/cppformat>`_,
|
|
4.7.2, 4.8.1 and Intel C++ Compiler (ICC) 14.0.2
|
|
|
|
* 32-bit (i386) GNU/Linux with GCC 4.4.3, 4.6.3
|
|
|
|
* Mac OS X with GCC 4.2.1 and Clang 4.2, 5.1.0
|
|
|
|
* 64-bit Windows with Visual C++ 2010 and
|
|
`2013 <https://ci.appveyor.com/project/vitaut/cppformat>`_
|
|
|
|
* 32-bit Windows with Visual C++ 2010
|
|
|
|
Although the library uses C++11 features when available, it also works with older
|
|
compilers and standard library implementations.
|
|
|
|
The output of all formatting functions is consistent across platforms. In particular,
|
|
formatting a floating-point infinity always gives ``inf`` while the output
|
|
of ``printf`` is platform-dependent in this case. For example,
|
|
|
|
.. code::
|
|
|
|
fmt::print("{}", std::numeric_limits<double>::infinity());
|
|
|
|
always prints ``inf``.
|
|
|
|
.. _ease-of-use:
|
|
|
|
Ease of Use
|
|
-----------
|
|
|
|
C++ Format has small self-contained code base consisting of a single header file
|
|
and a single source file and no external dependencies. A permissive BSD `license
|
|
<https://github.com/cppformat/cppformat#license>`_ allows using the library both
|
|
in open-source and commercial projects.
|
|
|
|
.. raw:: html
|
|
|
|
<a class="btn btn-success" href="https://github.com/cppformat/cppformat">GitHub Repository</a></p>
|
|
|
|
<div class="section footer">
|
|
<iframe src="http://ghbtns.com/github-btn.html?user=cppformat&repo=cppformat&type=watch&count=true"
|
|
class="github-btn" width="100" height="20"></iframe>
|
|
</div>
|