std::basic_format_args

 

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Formatting library

Formatting functions

format (C++20)

format_to (C++20)

format_to_n (C++20)

formatted_size (C++20)

vformat (C++20)

vformat_to (C++20)

Formatter

formatter (C++20)

basic_format_parse_contextformat_parse_contextwformat_parse_context (C++20)(C++20)(C++20)

basic_format_contextformat_contextwformat_context (C++20)(C++20)(C++20)

Formatting arguments

basic_format_arg (C++20)

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

visit_format_arg (C++20)

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

Format error

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

basic_format_args() noexcept;	(1)
template<class... Args> basic_format_args(const /*format-arg-store*/<Context, Args...>& store) noexcept;	(2)

1) Constructs a basic_format_args object that does not hold any formatting argument.

2) 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 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).

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).

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

See also

basic_format_arg (C++20)

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