Docs4dev
Docs
cpp / latest / utility / format / basic_format_context.html

std::basic_format_context

Defined in header <format> 
template< class OutputIt, class CharT >
class basic_format_context;
 (1) (since C++20) 
using format_context = basic_format_context</* unspecified */, char>;
 (2) (since C++20) 
using wformat_context = basic_format_context</* unspecified */, wchar_t>;
 (3) (since C++20)

Provides access to formatting state consisting of the formatting arguments and the output iterator.

The behavior is undefined if OutputIt does not model std::output_iterator<const CharT&>.

2) The unspecified template argument is an output iterator that appends to std::string, such as std::back_insert_iterator<std::string>. Implementations typically use an iterator to type-erased buffer type that supports appending to any contiguous and resizable container.
3) The unspecified template argument is an output iterator that appends to std::wstring.

Member types

Type Definition
iterator OutputIt
char_type CharT

Member alias templates

Type Definition
formatter_type<T> std::formatter<T, CharT>

Member functions

arg
returns the argument at the given index
(public member function)
locale
returns the locale used for locale-specific formatting
(public member function)
out
returns the iterator to output buffer
(public member function)
advance_to
advances the output iterator to the given position
(public member function)

std::basic_format_context::arg

std::basic_format_arg<basic_format_context> arg( std::size_t id ) const;

Returns a std::basic_format_arg holding the id-th argument in args, where args is the parameter pack or std::basic_format_args object passed to the formatting function.

If id is not less than the number of formatting arguments, returns a default-constructed std::basic_format_arg (holding a std::monostate object).

std::basic_format_context::locale

std::locale locale();

Returns the locale passed to the formatting function, or a default-constructed std::locale if the formatting function does not take a locale.

std::basic_format_context::out

iterator out();

Returns the iterator to the output buffer. The result is move-constructed from the stored iterator.

std::basic_format_context::advance_to

void advance_to( iterator it );

Move assigns it to the stored output iterator. After a call to advance_to, the next call to out() will return an iterator with the value that it had before the assignment.

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3567 C++20 basic_format_context does not work move-only iterator types made to move iterators

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/format/basic_format_context