std::basic_format_arg

basic_format_arg objects are typically created by std::make_format_args and accessed through std::visit_format_arg or the visit member functions(since C++26).

A basic_format_arg object behaves as if it contains a std::variant of the following types:

std::basic_format_arg::basic_format_arg

basic_format_arg() noexcept;

(since C++20)

Default constructor. Constructs a basic_format_arg that does not hold a formatting argument. The contained object has type std::monostate .

To create a basic_format_arg that holds a formatting argument, std::make_format_args has to be used.

explicit operator bool() const noexcept;

(since C++20)

Checks whether *this holds a formatting argument.

Returns true if *this holds a formatting argument (i.e. the contained object does not have type std::monostate ), false otherwise.

template< class Visitor >
decltype(auto) visit( this basic_format_arg arg, Visitor&& vis );

(1) (since C++26)

template< class R, class Visitor >
R visit( this basic_format_arg arg, Visitor&& vis );

(2) (since C++26)

Applies the visitor vis to the object contained in arg.

The visit functions do not modify the basic_format_arg object on which it is called because a copy of the object is used when calling vis.

1) Equivalent to return std::visit (std::forward <Visitor>(vis), v);, where v is the std::variant contained in arg.

2) Equivalent to return std::visit <R>(std::forward <Visitor>(vis), v);, where v is the std::variant contained in arg.

Feature-test macro	Value	Std	Feature
`__cpp_lib_format`	`202306L`	(C++26)	Member `visit`

This section is incomplete
Reason: no example

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

class that provides access to all formatting arguments
(class template) [edit]