# std::vformat

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< cpp‎ | utility‎ | format

Defined in header `<format>` |  |
std::string vformat( std::string_view fmt, std::format_args args ); | (1) | (since C++20)
std::wstring vformat( std::wstring_view fmt, std::wformat_args args ); | (2) | (since C++20)
std::string vformat( const std::locale& loc, std::string_view fmt, std::format_args args ); | (3) | (since C++20)
std::wstring vformat( const std::locale& loc, std::wstring_view fmt, std::wformat_args args ); | (4) | (since C++20)

Format arguments held by `args` according to the format string `fmt`, and return the result as a string. If present, `loc` is used for locale-specific formatting.

### Parameters

fmt | - | an object that represents the format string. The format string consists of ordinary characters (except { and }), which are copied unchanged to the output, escape sequences {{ and }}, which are replaced with { and } respectively in the output, and replacement fields. Each replacement field has the following format:
`{` arg-id (optional) `}` | (1) |
`{` arg-id (optional) `:` format-spec `}` | (2) |
1) replacement field without a format specification 2) replacement field with a format specification
arg-id | - | specifies the index of the argument in `args` whose value is to be used for formatting; if it is omitted, the arguments are used in order. The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error.
format-spec | - | the format specification defined by the std::formatter specialization for the corresponding argument.
For basic types and standard string types, the format specification is interpreted as standard format specification. For chrono types, the format specification is interpreted as chrono format specification. For std::thread::id, the format specification is interpreted as thread id format specification. For other formattable types, the format specification is determined by user-defined `formatter` specializations.
args | - | arguments to be formatted
loc | - | std::locale used for locale-specific formatting

### Return value

A string object holding the formatted result.

### Exceptions

Throws std::format_error if `fmt` is not a valid format string for the provided arguments, or std::bad_alloc on allocation failure. Also propagates any exception thrown by formatter or iterator operations.

### Example

Run this code

    #include <format>
    #include <iostream>

    template<typename... Args>
    inline void println(const std::format_string<Args...> fmt, Args&&... args)
    {
        std::cout << std::vformat(fmt.get(), std::make_format_args(args...)) << '\n';
    }

    int main()
    {
        println("{}{} {}{}", "Hello", ',', "C++", -1 + 2 * 3 * 4);
    }

Output:

    Hello, C++23

### See also

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