std::basic_format_arg(3)

💖 NAME 💖

std::basic_format_arg — std::basic_format_arg

Welcome to std::basic_format_arg(3), the page from the C++ Standard Libary manual — yes, “Libary” is literally what the header says, not me 💀. We are gonna get you comfy with formatting arguments, no cap, bestie 💅.

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✨ Synopsis ✨

Defined in header <format>.

template< class Context >   (since C++20)
class basic_format_arg;

Provides access to a formatting argument.

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 stores a std::variant of the following types:

• std::monostate (only if the object was default-constructed)
• bool
• Context::char_type
• int
• unsigned int
• long long int
• unsigned long long int
• float
• double
• long double
• const Context::char_type*
• std::basic_string_view<Context::char_type>
• const void*
• basic_format_arg::handle

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🎀 Member classes 🎀

• handle — type-erased wrapper that allows formatting an object of user-defined type; (C++20); (public member class)

🫶 Member functions 🫶

• constructor — constructs a std::basic_format_arg; (C++20); (public member function)
• operator bool — checks if the current object holds a formatting argument; (C++20); (public member function)
• visit — visit the stored formatting argument; (C++26); (public member function)

🌈 Non-member functions 🌈

• visit_format_arg — argument visitation interface for user-defined formatters; (C++20); (deprecated in C++26); (function template)

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🧚 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 stored object has type std::monostate.

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

🦋 std::basic_format_arg::operator bool 🦋

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 stored object does not have type std::monostate), false otherwise.

⭐ std::basic_format_arg::visit ⭐

1. template< class Visitor > (since C++26):

decltype(auto) visit( this basic_format_arg arg, Visitor&& vis );

2. template< class R, class Visitor > (since C++26):

R visit( this basic_format_arg arg, Visitor&& vis );

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

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🌸 Notes 🌸

🍓 Feature-test macro 🍓

• __cpp_lib_format — value 202306L; Std (C++26); Feature Member visit

🌟 Example 🌟

This section is incomplete Reason: no example

👑 See also 👑

• basic_format_args — (C++20)
• format_args — (C++20)
• wformat_args — (C++20); (class template); class that provides access to all formatting arguments

🎀 Category 🎀

• Todo no example

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Mwah 💋 — source http://cppreference.com, version/date 2024.06.10, page std::basic_format_arg(3). Slay your formatting era, bestie 🫶✨