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EQStream abstraction layer
This commit is contained in:
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.. _string-formatting-api:
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*************
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API Reference
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*************
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All functions and classes provided by the fmt library reside
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in namespace ``fmt`` and macros have prefix ``FMT_``. For brevity the
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namespace is usually omitted in examples.
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Format API
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==========
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The following functions use :ref:`format string syntax <syntax>` similar
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to the one used by Python's `str.format
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<http://docs.python.org/3/library/stdtypes.html#str.format>`_ function.
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They take *format_str* and *args* as arguments.
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*format_str* is a format string that contains literal text and replacement
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fields surrounded by braces ``{}``. The fields are replaced with formatted
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arguments in the resulting string.
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*args* is an argument list representing arbitrary arguments.
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.. _format:
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.. doxygenfunction:: format(CStringRef, ArgList)
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.. doxygenfunction:: operator""_format(const char *, std::size_t)
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.. _print:
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.. doxygenfunction:: print(CStringRef, ArgList)
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.. doxygenfunction:: print(std::FILE *, CStringRef, ArgList)
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.. doxygenclass:: fmt::BasicFormatter
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:members:
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Date and time formatting
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------------------------
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The library supports `strftime <http://en.cppreference.com/w/cpp/chrono/c/strftime>`_-like
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date and time formatting::
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#include "fmt/time.h"
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std::time_t t = std::time(nullptr);
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// Prints "The date is 2016-04-29." (with the current date)
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fmt::print("The date is {:%Y-%m-%d}.", *std::localtime(&t));
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The format string syntax is described in the documentation of
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`strftime <http://en.cppreference.com/w/cpp/chrono/c/strftime>`_.
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``std::ostream`` support
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------------------------
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The header ``fmt/ostream.h`` provides ``std::ostream`` support including
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formatting of user-defined types that have overloaded ``operator<<``::
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#include "fmt/ostream.h"
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class Date {
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int year_, month_, day_;
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public:
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Date(int year, int month, int day) : year_(year), month_(month), day_(day) {}
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friend std::ostream &operator<<(std::ostream &os, const Date &d) {
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return os << d.year_ << '-' << d.month_ << '-' << d.day_;
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}
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};
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std::string s = fmt::format("The date is {}", Date(2012, 12, 9));
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// s == "The date is 2012-12-9"
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.. doxygenfunction:: print(std::ostream&, CStringRef, ArgList)
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.. doxygenfunction:: fprintf(std::ostream&, CStringRef, ArgList)
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Argument formatters
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-------------------
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It is possible to change the way arguments are formatted by providing a
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custom argument formatter class::
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// A custom argument formatter that formats negative integers as unsigned
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// with the ``x`` format specifier.
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class CustomArgFormatter :
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public fmt::BasicArgFormatter<CustomArgFormatter, char> {
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public:
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CustomArgFormatter(fmt::BasicFormatter<char, CustomArgFormatter> &f,
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fmt::FormatSpec &s, const char *fmt)
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: fmt::BasicArgFormatter<CustomArgFormatter, char>(f, s, fmt) {}
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void visit_int(int value) {
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if (spec().type() == 'x')
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visit_uint(value); // convert to unsigned and format
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else
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fmt::BasicArgFormatter<CustomArgFormatter, char>::visit_int(value);
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}
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};
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std::string custom_format(const char *format_str, fmt::ArgList args) {
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fmt::MemoryWriter writer;
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// Pass custom argument formatter as a template arg to BasicFormatter.
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fmt::BasicFormatter<char, CustomArgFormatter> formatter(args, writer);
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formatter.format(format_str);
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return writer.str();
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}
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FMT_VARIADIC(std::string, custom_format, const char *)
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std::string s = custom_format("{:x}", -42); // s == "ffffffd6"
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.. doxygenclass:: fmt::ArgVisitor
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:members:
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.. doxygenclass:: fmt::BasicArgFormatter
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:members:
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.. doxygenclass:: fmt::ArgFormatter
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:members:
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Printf formatting functions
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---------------------------
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The following functions use `printf format string syntax
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<http://pubs.opengroup.org/onlinepubs/009695399/functions/fprintf.html>`_ with
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a POSIX extension for positional arguments.
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.. doxygenfunction:: printf(CStringRef, ArgList)
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.. doxygenfunction:: fprintf(std::FILE *, CStringRef, ArgList)
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.. doxygenfunction:: sprintf(CStringRef, ArgList)
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Write API
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=========
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.. doxygenclass:: fmt::BasicWriter
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:members:
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.. doxygenclass:: fmt::BasicMemoryWriter
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:members:
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.. doxygenclass:: fmt::BasicArrayWriter
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:members:
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.. doxygenfunction:: bin(int)
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.. doxygenfunction:: oct(int)
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.. doxygenfunction:: hex(int)
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.. doxygenfunction:: hexu(int)
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.. doxygenfunction:: pad(int, unsigned, Char)
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Utilities
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=========
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.. doxygenfunction:: fmt::arg(StringRef, const T&)
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.. doxygenfunction:: operator""_a(const char *, std::size_t)
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.. doxygendefine:: FMT_CAPTURE
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.. doxygendefine:: FMT_VARIADIC
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.. doxygenclass:: fmt::ArgList
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:members:
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.. doxygenclass:: fmt::BasicStringRef
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:members:
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.. doxygenclass:: fmt::BasicCStringRef
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:members:
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.. doxygenclass:: fmt::Buffer
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:protected-members:
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:members:
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System errors
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=============
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.. doxygenclass:: fmt::SystemError
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:members:
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.. doxygenclass:: fmt::WindowsError
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:members:
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.. _formatstrings:
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Custom allocators
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=================
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The fmt library supports custom dynamic memory allocators.
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A custom allocator class can be specified as a template argument to
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:class:`fmt::BasicMemoryWriter`::
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typedef fmt::BasicMemoryWriter<char, CustomAllocator> CustomMemoryWriter;
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It is also possible to write a formatting function that uses a custom
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allocator::
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typedef std::basic_string<char, std::char_traits<char>, CustomAllocator> CustomString;
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CustomString format(CustomAllocator alloc, fmt::CStringRef format_str,
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fmt::ArgList args) {
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CustomMemoryWriter writer(alloc);
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writer.write(format_str, args);
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return CustomString(writer.data(), writer.size(), alloc);
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}
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FMT_VARIADIC(CustomString, format, CustomAllocator, fmt::CStringRef)
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@@ -0,0 +1,10 @@
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########
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Contents
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########
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.. toctree::
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:maxdepth: 2
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usage
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api
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syntax
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@@ -0,0 +1,203 @@
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Overview
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========
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**fmt** (formerly cppformat) is an open-source formatting library.
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It can be used as a safe alternative to printf or as a fast
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alternative to C++ IOStreams.
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.. raw:: html
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<div class="panel panel-default">
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<div class="panel-heading">What users say:</div>
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<div class="panel-body">
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Thanks for creating this library. It’s been a hole in C++ for a long time.
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I’ve used both boost::format and loki::SPrintf, and neither felt like the
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right answer. This does.
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</div>
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</div>
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.. _format-api:
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Format API
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----------
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The replacement-based Format API provides a safe alternative to ``printf``,
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``sprintf`` and friends with comparable or `better performance
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<http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_.
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The `format string syntax <doc/latest/index.html#format-string-syntax>`_ is similar
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to the one used by `str.format <http://docs.python.org/2/library/stdtypes.html#str.format>`_
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in Python:
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.. code:: c++
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fmt::format("The answer is {}", 42);
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The ``fmt::format`` function returns a string "The answer is 42". You can use
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``fmt::MemoryWriter`` to avoid constructing ``std::string``:
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.. code:: c++
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fmt::MemoryWriter w;
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w.write("Look, a {} string", 'C');
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w.c_str(); // returns a C string (const char*)
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The ``fmt::print`` function performs formatting and writes the result to a file:
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.. code:: c++
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fmt::print(stderr, "System error code = {}\n", errno);
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The file argument can be omitted in which case the function prints to
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``stdout``:
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.. code:: c++
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fmt::print("Don't {}\n", "panic");
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If your compiler supports C++11, then the formatting functions are implemented
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with variadic templates. Otherwise variadic functions are emulated by generating
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a set of lightweight wrappers. This ensures compatibility with older compilers
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while providing a natural API.
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The Format API also supports positional arguments useful for localization:
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.. code:: c++
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fmt::print("I'd rather be {1} than {0}.", "right", "happy");
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Named arguments can be created with ``fmt::arg``. This makes it easier to track
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what goes where when multiple values are being inserted:
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.. code:: c++
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fmt::print("Hello, {name}! The answer is {number}. Goodbye, {name}.",
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fmt::arg("name", "World"), fmt::arg("number", 42));
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If your compiler supports C++11 user-defined literals, the suffix ``_a`` offers
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an alternative, slightly terser syntax for named arguments:
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.. code:: c++
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fmt::print("Hello, {name}! The answer is {number}. Goodbye, {name}.",
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"name"_a="World", "number"_a=42);
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The ``_format`` suffix may be used to format string literals similar to Python:
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.. code:: c++
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std::string message = "{0}{1}{0}"_format("abra", "cad");
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Other than the placement of the format string on the left of the operator,
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``_format`` is functionally identical to ``fmt::format``. In order to use the
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literal operators, they must be made visible with the directive
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``using namespace fmt::literals;``. Note that this brings in only ``_a`` and
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``_format`` but nothing else from the ``fmt`` namespace.
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.. _write-api:
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Write API
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---------
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The concatenation-based Write API (experimental) provides a
|
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`fast <http://zverovich.net/2013/09/07/integer-to-string-conversion-in-cplusplus.html>`_
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stateless alternative to IOStreams:
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.. code:: c++
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fmt::MemoryWriter out;
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out << "The answer in hexadecimal is " << hex(42);
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.. _safety:
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Safety
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------
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The library is fully type safe, automatic memory management prevents buffer overflow,
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errors in format strings are reported using exceptions. For example, the code
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.. code:: c++
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fmt::format("The answer is {:d}", "forty-two");
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throws a ``FormatError`` exception with description
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"unknown format code 'd' for string", because the argument
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``"forty-two"`` is a string while the format code ``d``
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only applies to integers.
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Where possible, errors are caught at compile time. For example, the code
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.. code:: c++
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fmt::format("Cyrillic letter {}", L'\x42e');
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produces a compile-time error because wide character ``L'\x42e'`` cannot be
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formatted into a narrow string. You can use a wide format string instead:
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.. code:: c++
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|
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fmt::format(L"Cyrillic letter {}", L'\x42e');
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For comparison, writing a wide character to ``std::ostream`` results in
|
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its numeric value being written to the stream (i.e. 1070 instead of letter 'ю' which
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is represented by ``L'\x42e'`` if we use Unicode) which is rarely what is needed.
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.. _portability:
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Portability
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-----------
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The library is highly portable. Here is an incomplete list of operating systems and
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compilers where it has been tested and known to work:
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* 64-bit (amd64) GNU/Linux with GCC 4.4.3, `4.6.3 <https://travis-ci.org/fmtlib/fmt>`_,
|
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4.7.2, 4.8.1 and Intel C++ Compiler (ICC) 14.0.2
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* 32-bit (i386) GNU/Linux with GCC 4.4.3, 4.6.3
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||||
|
||||
* Mac OS X with GCC 4.2.1 and Clang 4.2, 5.1.0
|
||||
|
||||
* 64-bit Windows with Visual C++ 2010, 2013 and
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`2015 <https://ci.appveyor.com/project/vitaut/fmt>`_
|
||||
|
||||
* 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 only thing to keep in mind
|
||||
for C++98 portability:
|
||||
|
||||
* Variadic templates: minimum GCC 4.4, Clang 2.9 or VS2013. This feature allows
|
||||
the Format API to accept an unlimited number of arguments. With older compilers
|
||||
the maximum is 15.
|
||||
|
||||
* User-defined literals: minimum GCC 4.7, Clang 3.1 or VS2015. The suffixes
|
||||
``_format`` and ``_a`` are functionally equivalent to the functions
|
||||
``fmt::format`` and ``fmt::arg``.
|
||||
|
||||
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
|
||||
-----------
|
||||
|
||||
fmt has a 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/fmtlib/fmt#license>`_ allows using the library both
|
||||
in open-source and commercial projects.
|
||||
|
||||
.. raw:: html
|
||||
|
||||
<a class="btn btn-success" href="https://github.com/fmtlib/fmt">GitHub Repository</a>
|
||||
|
||||
<div class="section footer">
|
||||
<iframe src="http://ghbtns.com/github-btn.html?user=fmtlib&repo=fmt&type=watch&count=true"
|
||||
class="github-btn" width="100" height="20"></iframe>
|
||||
</div>
|
||||
@@ -0,0 +1,406 @@
|
||||
.. _syntax:
|
||||
|
||||
********************
|
||||
Format String Syntax
|
||||
********************
|
||||
|
||||
Formatting functions such as :ref:`fmt::format() <format>` and :ref:`fmt::print() <print>`
|
||||
use the same format string syntax described in this section.
|
||||
|
||||
Format strings contain "replacement fields" surrounded by curly braces ``{}``.
|
||||
Anything that is not contained in braces is considered literal text, which is
|
||||
copied unchanged to the output. If you need to include a brace character in the
|
||||
literal text, it can be escaped by doubling: ``{{`` and ``}}``.
|
||||
|
||||
The grammar for a replacement field is as follows:
|
||||
|
||||
.. productionlist:: sf
|
||||
replacement_field: "{" [`arg_id`] [":" `format_spec`] "}"
|
||||
arg_id: `integer` | `identifier`
|
||||
integer: `digit`+
|
||||
digit: "0"..."9"
|
||||
identifier: `id_start` `id_continue`*
|
||||
id_start: "a"..."z" | "A"..."Z" | "_"
|
||||
id_continue: `id_start` | `digit`
|
||||
|
||||
In less formal terms, the replacement field can start with an *arg_id*
|
||||
that specifies the argument whose value is to be formatted and inserted into
|
||||
the output instead of the replacement field.
|
||||
The *arg_id* is optionally followed by a *format_spec*, which is preceded
|
||||
by a colon ``':'``. These specify a non-default format for the replacement value.
|
||||
|
||||
See also the :ref:`formatspec` section.
|
||||
|
||||
If the numerical arg_ids in a format string are 0, 1, 2, ... in sequence,
|
||||
they can all be omitted (not just some) and the numbers 0, 1, 2, ... will be
|
||||
automatically inserted in that order.
|
||||
|
||||
Some simple format string examples::
|
||||
|
||||
"First, thou shalt count to {0}" // References the first argument
|
||||
"Bring me a {}" // Implicitly references the first argument
|
||||
"From {} to {}" // Same as "From {0} to {1}"
|
||||
|
||||
The *format_spec* field contains a specification of how the value should be
|
||||
presented, including such details as field width, alignment, padding, decimal
|
||||
precision and so on. Each value type can define its own "formatting
|
||||
mini-language" or interpretation of the *format_spec*.
|
||||
|
||||
Most built-in types support a common formatting mini-language, which is
|
||||
described in the next section.
|
||||
|
||||
A *format_spec* field can also include nested replacement fields within it.
|
||||
These nested replacement fields can contain only an argument index;
|
||||
format specifications are not allowed. Formatting is performed as if the
|
||||
replacement fields within the format_spec are substituted before the
|
||||
*format_spec* string is interpreted. This allows the formatting of a value
|
||||
to be dynamically specified.
|
||||
|
||||
See the :ref:`formatexamples` section for some examples.
|
||||
|
||||
.. _formatspec:
|
||||
|
||||
Format Specification Mini-Language
|
||||
==================================
|
||||
|
||||
"Format specifications" are used within replacement fields contained within a
|
||||
format string to define how individual values are presented (see
|
||||
:ref:`syntax`). Each formattable type may define how the format
|
||||
specification is to be interpreted.
|
||||
|
||||
Most built-in types implement the following options for format specifications,
|
||||
although some of the formatting options are only supported by the numeric types.
|
||||
|
||||
The general form of a *standard format specifier* is:
|
||||
|
||||
.. productionlist:: sf
|
||||
format_spec: [[`fill`]`align`][`sign`]["#"]["0"][`width`]["." `precision`][`type`]
|
||||
fill: <a character other than '{' or '}'>
|
||||
align: "<" | ">" | "=" | "^"
|
||||
sign: "+" | "-" | " "
|
||||
width: `integer` | "{" `arg_id` "}"
|
||||
precision: `integer` | "{" `arg_id` "}"
|
||||
type: `int_type` | "c" | "e" | "E" | "f" | "F" | "g" | "G" | "p" | "s"
|
||||
int_type: "b" | "B" | "d" | "o" | "x" | "X"
|
||||
|
||||
The *fill* character can be any character other than '{' or '}'. The presence
|
||||
of a fill character is signaled by the character following it, which must be
|
||||
one of the alignment options. If the second character of *format_spec* is not
|
||||
a valid alignment option, then it is assumed that both the fill character and
|
||||
the alignment option are absent.
|
||||
|
||||
The meaning of the various alignment options is as follows:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Option | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'<'`` | Forces the field to be left-aligned within the available |
|
||||
| | space (this is the default for most objects). |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'>'`` | Forces the field to be right-aligned within the |
|
||||
| | available space (this is the default for numbers). |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'='`` | Forces the padding to be placed after the sign (if any) |
|
||||
| | but before the digits. This is used for printing fields |
|
||||
| | in the form '+000000120'. This alignment option is only |
|
||||
| | valid for numeric types. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'^'`` | Forces the field to be centered within the available |
|
||||
| | space. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
Note that unless a minimum field width is defined, the field width will always
|
||||
be the same size as the data to fill it, so that the alignment option has no
|
||||
meaning in this case.
|
||||
|
||||
The *sign* option is only valid for number types, and can be one of the
|
||||
following:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Option | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'+'`` | indicates that a sign should be used for both |
|
||||
| | positive as well as negative numbers. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'-'`` | indicates that a sign should be used only for negative |
|
||||
| | numbers (this is the default behavior). |
|
||||
+---------+----------------------------------------------------------+
|
||||
| space | indicates that a leading space should be used on |
|
||||
| | positive numbers, and a minus sign on negative numbers. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
The ``'#'`` option causes the "alternate form" to be used for the
|
||||
conversion. The alternate form is defined differently for different
|
||||
types. This option is only valid for integer and floating-point types.
|
||||
For integers, when binary, octal, or hexadecimal output is used, this
|
||||
option adds the prefix respective ``"0b"`` (``"0B"``), ``"0"``, or
|
||||
``"0x"`` (``"0X"``) to the output value. Whether the prefix is
|
||||
lower-case or upper-case is determined by the case of the type
|
||||
specifier, for example, the prefix ``"0x"`` is used for the type ``'x'``
|
||||
and ``"0X"`` is used for ``'X'``. For floating-point numbers the
|
||||
alternate form causes the result of the conversion to always contain a
|
||||
decimal-point character, even if no digits follow it. Normally, a
|
||||
decimal-point character appears in the result of these conversions
|
||||
only if a digit follows it. In addition, for ``'g'`` and ``'G'``
|
||||
conversions, trailing zeros are not removed from the result.
|
||||
|
||||
.. ifconfig:: False
|
||||
|
||||
The ``','`` option signals the use of a comma for a thousands separator.
|
||||
For a locale aware separator, use the ``'n'`` integer presentation type
|
||||
instead.
|
||||
|
||||
*width* is a decimal integer defining the minimum field width. If not
|
||||
specified, then the field width will be determined by the content.
|
||||
|
||||
Preceding the *width* field by a zero (``'0'``) character enables
|
||||
sign-aware zero-padding for numeric types. This is equivalent to a *fill*
|
||||
character of ``'0'`` with an *alignment* type of ``'='``.
|
||||
|
||||
The *precision* is a decimal number indicating how many digits should be
|
||||
displayed after the decimal point for a floating-point value formatted with
|
||||
``'f'`` and ``'F'``, or before and after the decimal point for a floating-point
|
||||
value formatted with ``'g'`` or ``'G'``. For non-number types the field
|
||||
indicates the maximum field size - in other words, how many characters will be
|
||||
used from the field content. The *precision* is not allowed for integer,
|
||||
character, Boolean, and pointer values.
|
||||
|
||||
Finally, the *type* determines how the data should be presented.
|
||||
|
||||
The available string presentation types are:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Type | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'s'`` | String format. This is the default type for strings and |
|
||||
| | may be omitted. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| none | The same as ``'s'``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
The available character presentation types are:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Type | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'c'`` | Character format. This is the default type for |
|
||||
| | characters and may be omitted. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| none | The same as ``'c'``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
The available integer presentation types are:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Type | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'b'`` | Binary format. Outputs the number in base 2. Using the |
|
||||
| | ``'#'`` option with this type adds the prefix ``"0b"`` |
|
||||
| | to the output value. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'B'`` | Binary format. Outputs the number in base 2. Using the |
|
||||
| | ``'#'`` option with this type adds the prefix ``"0B"`` |
|
||||
| | to the output value. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'d'`` | Decimal integer. Outputs the number in base 10. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'o'`` | Octal format. Outputs the number in base 8. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'x'`` | Hex format. Outputs the number in base 16, using |
|
||||
| | lower-case letters for the digits above 9. Using the |
|
||||
| | ``'#'`` option with this type adds the prefix ``"0x"`` |
|
||||
| | to the output value. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'X'`` | Hex format. Outputs the number in base 16, using |
|
||||
| | upper-case letters for the digits above 9. Using the |
|
||||
| | ``'#'`` option with this type adds the prefix ``"0X"`` |
|
||||
| | to the output value. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'n'`` | Number. This is the same as ``'d'``, except that it uses |
|
||||
| | the current locale setting to insert the appropriate |
|
||||
| | number separator characters. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| none | The same as ``'d'``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
Integer presentation types can also be used with character and Boolean values.
|
||||
Boolean values are formatted using textual representation, either ``true`` or
|
||||
``false``, if the presentation type is not specified.
|
||||
|
||||
The available presentation types for floating-point values are:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Type | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'a'`` | Hexadecimal floating point format. Prints the number in |
|
||||
| | base 16 with prefix ``"0x"`` and lower-case letters for |
|
||||
| | digits above 9. Uses 'p' to indicate the exponent. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'A'`` | Same as ``'a'`` except it uses upper-case letters for |
|
||||
| | the prefix, digits above 9 and to indicate the exponent. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'e'`` | Exponent notation. Prints the number in scientific |
|
||||
| | notation using the letter 'e' to indicate the exponent. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'E'`` | Exponent notation. Same as ``'e'`` except it uses an |
|
||||
| | upper-case 'E' as the separator character. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'f'`` | Fixed point. Displays the number as a fixed-point |
|
||||
| | number. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'F'`` | Fixed point. Same as ``'f'``, but converts ``nan`` to |
|
||||
| | ``NAN`` and ``inf`` to ``INF``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'g'`` | General format. For a given precision ``p >= 1``, |
|
||||
| | this rounds the number to ``p`` significant digits and |
|
||||
| | then formats the result in either fixed-point format |
|
||||
| | or in scientific notation, depending on its magnitude. |
|
||||
| | |
|
||||
| | A precision of ``0`` is treated as equivalent to a |
|
||||
| | precision of ``1``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| ``'G'`` | General format. Same as ``'g'`` except switches to |
|
||||
| | ``'E'`` if the number gets too large. The |
|
||||
| | representations of infinity and NaN are uppercased, too. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| none | The same as ``'g'``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
Floating-point formatting is locale-dependent.
|
||||
|
||||
.. ifconfig:: False
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| | The precise rules are as follows: suppose that the |
|
||||
| | result formatted with presentation type ``'e'`` and |
|
||||
| | precision ``p-1`` would have exponent ``exp``. Then |
|
||||
| | if ``-4 <= exp < p``, the number is formatted |
|
||||
| | with presentation type ``'f'`` and precision |
|
||||
| | ``p-1-exp``. Otherwise, the number is formatted |
|
||||
| | with presentation type ``'e'`` and precision ``p-1``. |
|
||||
| | In both cases insignificant trailing zeros are removed |
|
||||
| | from the significand, and the decimal point is also |
|
||||
| | removed if there are no remaining digits following it. |
|
||||
| | |
|
||||
| | Positive and negative infinity, positive and negative |
|
||||
| | zero, and nans, are formatted as ``inf``, ``-inf``, |
|
||||
| | ``0``, ``-0`` and ``nan`` respectively, regardless of |
|
||||
| | the precision. |
|
||||
| | |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
The available presentation types for pointers are:
|
||||
|
||||
+---------+----------------------------------------------------------+
|
||||
| Type | Meaning |
|
||||
+=========+==========================================================+
|
||||
| ``'p'`` | Pointer format. This is the default type for |
|
||||
| | pointers and may be omitted. |
|
||||
+---------+----------------------------------------------------------+
|
||||
| none | The same as ``'p'``. |
|
||||
+---------+----------------------------------------------------------+
|
||||
|
||||
.. _formatexamples:
|
||||
|
||||
Format examples
|
||||
===============
|
||||
|
||||
This section contains examples of the format syntax and comparison with
|
||||
the printf formatting.
|
||||
|
||||
In most of the cases the syntax is similar to the printf formatting, with the
|
||||
addition of the ``{}`` and with ``:`` used instead of ``%``.
|
||||
For example, ``"%03.2f"`` can be translated to ``"{:03.2f}"``.
|
||||
|
||||
The new format syntax also supports new and different options, shown in the
|
||||
following examples.
|
||||
|
||||
Accessing arguments by position::
|
||||
|
||||
format("{0}, {1}, {2}", 'a', 'b', 'c');
|
||||
// Result: "a, b, c"
|
||||
format("{}, {}, {}", 'a', 'b', 'c');
|
||||
// Result: "a, b, c"
|
||||
format("{2}, {1}, {0}", 'a', 'b', 'c');
|
||||
// Result: "c, b, a"
|
||||
format("{0}{1}{0}", "abra", "cad"); // arguments' indices can be repeated
|
||||
// Result: "abracadabra"
|
||||
|
||||
Aligning the text and specifying a width::
|
||||
|
||||
format("{:<30}", "left aligned");
|
||||
// Result: "left aligned "
|
||||
format("{:>30}", "right aligned");
|
||||
// Result: " right aligned"
|
||||
format("{:^30}", "centered");
|
||||
// Result: " centered "
|
||||
format("{:*^30}", "centered"); // use '*' as a fill char
|
||||
// Result: "***********centered***********"
|
||||
|
||||
Replacing ``%+f``, ``%-f``, and ``% f`` and specifying a sign::
|
||||
|
||||
format("{:+f}; {:+f}", 3.14, -3.14); // show it always
|
||||
// Result: "+3.140000; -3.140000"
|
||||
format("{: f}; {: f}", 3.14, -3.14); // show a space for positive numbers
|
||||
// Result: " 3.140000; -3.140000"
|
||||
format("{:-f}; {:-f}", 3.14, -3.14); // show only the minus -- same as '{:f}; {:f}'
|
||||
// Result: "3.140000; -3.140000"
|
||||
|
||||
Replacing ``%x`` and ``%o`` and converting the value to different bases::
|
||||
|
||||
format("int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}", 42);
|
||||
// Result: "int: 42; hex: 2a; oct: 52; bin: 101010"
|
||||
// with 0x or 0 or 0b as prefix:
|
||||
format("int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}", 42);
|
||||
// Result: "int: 42; hex: 0x2a; oct: 052; bin: 0b101010"
|
||||
|
||||
.. ifconfig:: False
|
||||
|
||||
Using the comma as a thousands separator::
|
||||
|
||||
format("{:,}", 1234567890);
|
||||
'1,234,567,890'
|
||||
|
||||
Expressing a percentage::
|
||||
|
||||
>>> points = 19
|
||||
>>> total = 22
|
||||
Format("Correct answers: {:.2%}") << points/total)
|
||||
'Correct answers: 86.36%'
|
||||
|
||||
Using type-specific formatting::
|
||||
|
||||
>>> import datetime
|
||||
>>> d = datetime.datetime(2010, 7, 4, 12, 15, 58)
|
||||
Format("{:%Y-%m-%d %H:%M:%S}") << d)
|
||||
'2010-07-04 12:15:58'
|
||||
|
||||
Nesting arguments and more complex examples::
|
||||
|
||||
>>> for align, text in zip('<^>', ['left', 'center', 'right']):
|
||||
... '{0:{fill}{align}16}") << text, fill=align, align=align)
|
||||
...
|
||||
'left<<<<<<<<<<<<'
|
||||
'^^^^^center^^^^^'
|
||||
'>>>>>>>>>>>right'
|
||||
>>>
|
||||
>>> octets = [192, 168, 0, 1]
|
||||
Format("{:02X}{:02X}{:02X}{:02X}") << *octets)
|
||||
'C0A80001'
|
||||
>>> int(_, 16)
|
||||
3232235521
|
||||
>>>
|
||||
>>> width = 5
|
||||
>>> for num in range(5,12):
|
||||
... for base in 'dXob':
|
||||
... print('{0:{width}{base}}") << num, base=base, width=width), end=' ')
|
||||
... print()
|
||||
...
|
||||
5 5 5 101
|
||||
6 6 6 110
|
||||
7 7 7 111
|
||||
8 8 10 1000
|
||||
9 9 11 1001
|
||||
10 A 12 1010
|
||||
11 B 13 1011
|
||||
|
||||
@@ -0,0 +1,90 @@
|
||||
*****
|
||||
Usage
|
||||
*****
|
||||
|
||||
To use the fmt library, add :file:`format.h` and :file:`format.cc` from
|
||||
a `release archive <https://github.com/fmtlib/fmt/releases/latest>`_
|
||||
or the `Git repository <https://github.com/fmtlib/fmt>`_ to your project.
|
||||
Alternatively, you can :ref:`build the library with CMake <building>`.
|
||||
|
||||
If you are using Visual C++ with precompiled headers, you might need to add
|
||||
the line ::
|
||||
|
||||
#include "stdafx.h"
|
||||
|
||||
before other includes in :file:`format.cc`.
|
||||
|
||||
.. _building:
|
||||
|
||||
Building the library
|
||||
====================
|
||||
|
||||
The included `CMake build script`__ can be used to build the fmt
|
||||
library on a wide range of platforms. CMake is freely available for
|
||||
download from http://www.cmake.org/download/.
|
||||
|
||||
__ https://github.com/fmtlib/fmt/blob/master/CMakeLists.txt
|
||||
|
||||
CMake works by generating native makefiles or project files that can
|
||||
be used in the compiler environment of your choice. The typical
|
||||
workflow starts with::
|
||||
|
||||
mkdir build # Create a directory to hold the build output.
|
||||
cd build
|
||||
cmake <path/to/fmt> # Generate native build scripts.
|
||||
|
||||
where :file:`{<path/to/fmt>}` is a path to the ``fmt`` repository.
|
||||
|
||||
If you are on a \*nix system, you should now see a Makefile in the
|
||||
current directory. Now you can build the library by running :command:`make`.
|
||||
|
||||
Once the library has been built you can invoke :command:`make test` to run
|
||||
the tests.
|
||||
|
||||
If you use Windows and have Visual Studio installed, a :file:`FORMAT.sln`
|
||||
file and several :file:`.vcproj` files will be created. You can then build them
|
||||
using Visual Studio or msbuild.
|
||||
|
||||
On Mac OS X with Xcode installed, an :file:`.xcodeproj` file will be generated.
|
||||
|
||||
To build a `shared library`__ set the ``BUILD_SHARED_LIBS`` CMake variable to
|
||||
``TRUE``::
|
||||
|
||||
cmake -DBUILD_SHARED_LIBS=TRUE ...
|
||||
|
||||
__ http://en.wikipedia.org/wiki/Library_%28computing%29#Shared_libraries
|
||||
|
||||
Building the documentation
|
||||
==========================
|
||||
|
||||
To build the documentation you need the following software installed on your
|
||||
system:
|
||||
|
||||
* `Python <https://www.python.org/>`_ with pip and virtualenv
|
||||
* `Doxygen <http://www.stack.nl/~dimitri/doxygen/>`_
|
||||
* `Less <http://lesscss.org/>`_ with less-plugin-clean-css
|
||||
|
||||
First generate makefiles or project files using CMake as described in
|
||||
the previous section. Then compile the ``doc`` target/project, for example::
|
||||
|
||||
make doc
|
||||
|
||||
This will generate the HTML documentation in ``doc/html``.
|
||||
|
||||
Android NDK
|
||||
===========
|
||||
|
||||
fmt provides `Android.mk file`__ that can be used to build the library
|
||||
with `Android NDK <https://developer.android.com/tools/sdk/ndk/index.html>`_.
|
||||
For an example of using fmt with Android NDK, see the
|
||||
`android-ndk-example <https://github.com/fmtlib/android-ndk-example>`_
|
||||
repository.
|
||||
|
||||
__ https://github.com/fmtlib/fmt/blob/master/Android.mk
|
||||
|
||||
Homebrew
|
||||
========
|
||||
|
||||
fmt can be installed on OS X using `Homebrew <http://brew.sh/>`_::
|
||||
|
||||
brew install cppformat
|
||||
Reference in New Issue
Block a user