NAME¶

std::basic_format_context - std::basic_format_context

Synopsis¶

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

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

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.

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

A program that declares an explicit or partial specialization of
std::basic_format_context is ill-formed, no diagnostic required.

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¶

This section is incomplete
Reason: no 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 made to move
iterator types iterators
LWG 3975 C++20 user specialization of basic_format_context disallowed
was allowed

Category:¶

* Todo no example