std::basic_format_args

 

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format_to (C++20)

format_to_n (C++20)

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vformat_to (C++20)

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basic_format_stringformat_stringwformat_string (C++20)(C++20)(C++20)

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formattable (C++23)

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basic_format_arg (C++20)

basic_format_arg::handle (C++20)

basic_format_argsformat_argswformat_args (C++20)(C++20)(C++20)

visit_format_arg (C++20) (deprecated in C++26)

make_format_argsmake_wformat_args (C++20)(C++20)

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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).

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

basic_format_arg (C++20)

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