std::make_format_args, std::make_wformat_args

< cpp‎ | utility‎ | format
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions
Formatting library
Formatting functions
Formatting arguments
Format error
Defined in header <format>
template< class Context = std::format_context, class... Args >

/*format-arg-store*/<Context, Args...>

    make_format_args( Args&&... args );
(1) (since C++20)
template< class... Args >

/*format-arg-store*/<std::wformat_context, Args...>

    make_wformat_args( 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 BasicFormatter requirements for any Ti in Args.


[edit] Parameters

args... - values to be used as formatting arguments

[edit] Returns

An object that holds the formatting arguments.

[edit] 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.

[edit] Example

#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{}, std::make_format_args(args...));
int main()
    log("Number", "of", "arguments", "is", "arbitrary.");
    log("Any type that meets the `BasicFormatter` 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"));


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

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2418R2 C++20 objects that are neither const-usable nor copyable
(such as generator-like objects) are not formattable
allow formatting these objects

[edit] See also

class that provides access to all formatting arguments
(class template) [edit]
non-template variant of std::format using type-erased argument representation
(function) [edit]
non-template variant of std::format_to using type-erased argument representation
(function template) [edit]