reference.rst

API Reference

All functions and classes provided by the C++ Format library reside in namespace fmt and macros have prefix FMT_. For brevity the namespace is usually omitted in examples.

Formatting functions

The following functions use :ref:`format string syntax <syntax>` similar to the one used by Python's str.format function. They take format_str and args as arguments.

format_str is a format string that contains literal text and replacement fields surrounded by braces {}. The fields are replaced with formatted arguments in the resulting string.

args is an argument list representing arbitrary arguments.

.. doxygenfunction:: fmt::format(StringRef, ArgList)

.. doxygenfunction:: fmt::print(StringRef, ArgList)

.. doxygenfunction:: fmt::print(std::FILE *, StringRef, ArgList)

.. doxygenfunction:: fmt::print(std::ostream &, StringRef, ArgList)

Printf formatting functions

The following functions use printf format string syntax with a POSIX extension for positional arguments.

.. doxygenfunction:: fmt::printf(StringRef, ArgList)

.. doxygenfunction:: fmt::fprintf(std::FILE *, StringRef, ArgList)

.. doxygenfunction:: fmt::sprintf(StringRef, ArgList)

Write API

.. doxygenclass:: fmt::BasicWriter
   :members:

.. doxygenclass:: fmt::BasicMemoryWriter
   :members:

.. doxygenfunction:: fmt::bin

.. doxygenfunction:: fmt::oct

.. doxygenfunction:: fmt::hex

.. doxygenfunction:: fmt::hexu

.. doxygenfunction:: fmt::pad(int, unsigned, Char)

Utilities

.. doxygendefine:: FMT_VARIADIC

.. doxygenclass:: fmt::ArgList
   :members:

.. doxygenclass:: fmt::BasicStringRef
   :members:

System Errors

.. doxygenclass:: fmt::SystemError
   :members:

.. doxygenclass:: fmt::WindowsError
   :members:

Custom allocators

The C++ Format library supports custom dynamic memory allocators. A custom allocator class can be specified as a template argument to :cpp:class:`fmt::BasicMemoryWriter`:

typedef fmt::BasicMemoryWriter<char, CustomAllocator> CustomMemoryWriter;

It is also possible to write a formatting function that uses a custom allocator:

typedef std::basic_string<char, std::char_traits<char>, CustomAllocator> CustomString;

CustomString format(CustomAllocator alloc, fmt::StringRef format_str,
                    fmt::ArgList args) {
  CustomMemoryWriter writer(alloc);
  writer.write(format_str, args);
  return CustomString(writer.data(), writer.size(), alloc);
}
FMT_VARIADIC(CustomString, format, CustomAllocator, fmt::StringRef)