std::basic_format_args - cppreference.com

From cppreference.com

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

	constructs a `basic_format_args` object (public member function)
	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

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