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Difference between revisions of "cpp/utility/format/basic format args"

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===Defect reports===
 
===Defect reports===
 
{{dr list begin}}
 
{{dr list begin}}
−
{{dr list item|paper=P2216R3|std=C++20|before=|after={{tt|format_args_t}} is removed}}
+
{{dr list item|paper=P2216R3|std=C++20|before={{tt|format_args_t}} was provided due to overparameterization of {{tt|vformat_to}}|after=removed}}
 
{{dr list end}}
 
{{dr list end}}
  

Revision as of 11:00, 19 June 2021

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Formatting library
Standard format specification
Formatting functions
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Format strings
(C++20)(C++20)(C++20)
(C++26)
Formatting concepts
(C++23)
Formatter
(C++20)
(C++23)
(C++23)
(C++23)
(C++23)
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
(C++23)
(C++23)
Formatting arguments
(C++20)
(C++20)
basic_format_argsformat_argswformat_args
(C++20)(C++20)(C++20)
(C++20) (deprecated in C++26)
(C++20)(C++20)
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.

Contents

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).

Example

This section is incomplete
Reason: no 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

See also

(C++20)
 class template that provides access to a formatting argument for user-defined formatters
(class template) [edit]
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