std:: basic_format_args

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Formatting library
Standard format specification
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Formatter
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Formatting arguments
(C++20)
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basic_format_args format_args wformat_args
(C++20) (C++20) (C++20)
(C++20) (deprecated in C++26)
(C++20) (C++20)
Format error
(C++20)
Defined in header <format>
template < class Context >
class basic_format_args ;
(1) (since C++20)
using format_args = basic_format_args < std:: format_context > ;
(2) (since C++20)
using wformat_args = basic_format_args < std:: wformat_context > ;
(3) (since C++20)

Provides access to formatting arguments.

Member functions

(constructor)
constructs a basic_format_args object
(public member function)
get
returns formatting argument at the given index
(public member function)

std::basic_format_args:: basic_format_args

template < class ... Args >
basic_format_args ( const /*format-arg-store*/ < Context, Args... > & store ) noexcept ;

Constructs a basic_format_args object from the result of a call to std::make_format_args or std::make_wformat_args .

std::basic_format_args:: get

std:: basic_format_arg < Context > get ( std:: size_t i ) const noexcept ;

Returns a std::basic_format_arg holding the i -th argument in args , where args is the parameter pack passed to std::make_format_args or std::make_wformat_args .

If there's no such formatting argument (i.e. * this was default-constructed or i is not less than the number of formatting arguments), returns a default-constructed std::basic_format_arg (holding a std::monostate object).

Deduction guides

template < class Context, class ... Args >
basic_format_args ( /*format-arg-store*/ < Context, Args... > ) - > basic_format_args < Context > ;
(since C++20)

Notes

std::basic_format_args has reference semantics. It is the programmer's responsibility to ensure that * this does not outlive store (which, in turn, should not outlive the arguments to std::make_format_args or std::make_wformat_args ).

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
P2216R3 C++20 format_args_t was provided due to overparameterization of vformat_to removed
LWG 3810 C++20 basic_format_args has no deduction guide added
LWG 4106 C++20 basic_format_args was default-constructible default constructor removed

See also

(C++20)
class template that provides access to a formatting argument for user-defined formatters
(class template)
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