std::make_format_args, std::make_wformat_args

 

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Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

Formatting library

Standard format specification

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)

Format strings

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

runtime_format (C++26)

Formatting concepts

formattable (C++23)

Formatter

formatter (C++20)

formatter<pair-or-tuple> (C++23)

formatter<range> (C++23)

range_formatter (C++23)

enable_nonlocking_formatter_optimization (C++23)

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)

range_format (C++23)

format_kind (C++23)

Formatting arguments

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)

Format error

format_error (C++20)

 

Defined in header <format>
template<class Context = std::format_context, class... Args> /*format-arg-store*/<Context, Args...> make_format_args(const Args&... args);	(1)	(since C++20)
template<class... Args> /*format-arg-store*/<std::wformat_context, Args...> make_wformat_args(const Args&... args);	(2)	(since C++20)

Returns an object that stores an array of formatting arguments and can be implicitly converted to std::basic_format_args<Context>.

The behavior is undefined if typename Context::template formatter_type<Ti> does not meet the Formatter requirements for any Ti in Args.

Parameters

args...

-

values to be used as formatting arguments

Returns

An object that holds the formatting arguments.

Notes

A formatting argument has reference semantics for user-defined types and does not extend the lifetime of args. It is the programmer's responsibility to ensure that args outlive the return value. Usually, the result is only used as argument to formatting function.

Example

Run this code

#include <array>
#include <format>
#include <iostream>
#include <string_view>
 
void raw_write_to_log(std::string_view users_fmt, std::format_args&& args) {
    static int n{};
    std::clog << std::format("{:04} : ", n++) << std::vformat(users_fmt, args) << '\n';
}
 
template <typename... Args>
constexpr void log(Args&&... args) {
 
    // Generate formatting string "{} "...
    std::array<char, sizeof...(Args) * 3 + 1> braces{};
    constexpr const char c[4] = "{} ";
    for (auto i{0u}; i != braces.size() - 1; ++i) {
        braces[i] = c[i % 3];
    }
    braces.back() = '\0';
 
    raw_write_to_log(std::string_view{braces.data()}, std::make_format_args(args...));
}
 
int main()
{
    log("Number", "of", "arguments", "is", "arbitrary.");
    log("Any type that meets the `Formatter` requirements", "can be printed.");
    log("For example:", 1, 2.0, '3', "*42*");
 
    raw_write_to_log("{:02} │ {} │ {} │ {}", std::make_format_args(1, 2.0, '3', "4"));
}

Output:

0000 : Number of arguments is arbitrary. 
0001 : Any type that meets the `Formatter` requirements can be printed. 
0002 : For example: 1 2.0 3 *42* 
0003 : 01 │ 2.0 │ 3 │ 4

See also

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

class that provides access to all formatting arguments (class template)