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&>.
std::string, such as
std::back_insert_iterator<std::string>. Implementations are encouraged to use an iterator to type-erased buffer type that supports appending to any contiguous and resizable container.
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 |
See also
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https://en.cppreference.com/w/cpp/utility/format/basic_format_context
