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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../utility/to_chars.html below:

std::to_chars - cppreference.com

std::to_chars_result to_chars( char* first, char* last, /* integer-type */ value, int base = 10 ); (1) (since C++17)
(constexpr since C++23)

std::to_chars_result to_chars( char*, char*, bool, int = 10 ) = delete;

(2) (since C++17)

std::to_chars_result to_chars( char* first, char* last, /* floating-point-type */ value );

(3) (since C++17) std::to_chars_result to_chars( char* first, char* last, /* floating-point-type */ value, std::chars_format fmt ); (4) (since C++17) std::to_chars_result to_chars( char* first, char* last, /* floating-point-type */ value, std::chars_format fmt, int precision ); (5) (since C++17)

Converts value into a character string by successively filling the range [first, last), where [first, last) is required to be a valid range.

1) Integer formatters: value is converted to a string of digits in the given base (with no redundant leading zeroes). Digits in the range 10..35 (inclusive) are represented as lowercase characters a..z. If value is less than zero, the representation starts with a minus sign. The library provides overloads for all cv-unqualified signed and unsigned integer types and for the type char as the type of the parameter value.

2) Overload for bool is deleted. std::to_chars rejects argument of type bool because the result would be "0"/"1" but not "false"/"true" if it is permitted.

3) value

is converted to a string in the style of

std::printf

in the default ("C") locale. The conversion specifier is

f

e

(resolving in favor of

f

in case of a tie), chosen according to the requirement for a shortest representation: the string representation consists of the smallest number of characters such that there is at least one digit before the radix point (if present) and parsing the representation using the corresponding

std::from_chars

function recovers value exactly. If there are several such representations, one with the smallest difference to

value

is chosen, resolving any remaining ties using rounding according to

std::round_to_nearest

. The library provides overloads for all cv-unqualified

standard(until C++23)

floating-point types as the type of the parameter

value

5) Same as (4), except the precision is specified by the parameter precision rather than by the shortest representation requirement. The library provides overloads for all cv-unqualified standard(until C++23) floating-point types as the type of the parameter value.

[edit] Parameters first, last - character range to write to value - the value to convert to its string representation base - integer base to use: a value between 2 and 36 (inclusive). fmt - floating-point formatting to use, a bitmask of type std::chars_format precision - floating-point precision to use [edit] Return value

On success, returns a value of type std::to_chars_result such that ec equals value-initialized std::errc and ptr is the one-past-the-end pointer of the characters written. Note that the string is not NUL-terminated.

On error, returns a value of type std::to_chars_result holding std::errc::value_too_large in ec, a copy of the value last in ptr, and leaves the contents of the range [first, last) in unspecified state.

[edit] Exceptions

Throws nothing.

[edit] Notes

Unlike other formatting functions in C++ and C libraries, std::to_chars is locale-independent, non-allocating, and non-throwing. Only a small subset of formatting policies used by other libraries (such as std::sprintf) is provided. This is intended to allow the fastest possible implementation that is useful in common high-throughput contexts such as text-based interchange (JSON or XML).

The guarantee that std::from_chars can recover every floating-point value formatted by std::to_chars exactly is only provided if both functions are from the same implementation.

To format a bool value as "0"/"1" using std::to_chars, the value must be cast to another integer type.

[edit] Example

#include <charconv>
#include <iomanip>
#include <iostream>
#include <string_view>
#include <system_error>
 
void show_to_chars(auto... format_args)
{
    const size_t buf_size = 10;
    char buf[buf_size]{};
    std::to_chars_result result = std::to_chars(buf, buf + buf_size, format_args...);
 
    if (result.ec != std::errc())
        std::cout << std::make_error_code(result.ec).message() << '\n';
    else
    {
        std::string_view str(buf, result.ptr - buf);
        std::cout << std::quoted(str) << '\n';
    }
}
 
int main()
{
    show_to_chars(42);
    show_to_chars(+3.14159F);
    show_to_chars(-3.14159, std::chars_format::fixed);
    show_to_chars(-3.14159, std::chars_format::scientific, 3);
    show_to_chars(3.1415926535, std::chars_format::fixed, 10);
}

Possible output:

"42"
"3.14159"
"-3.14159"
"-3.142e+00"
Value too large for defined data type

[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 LWG 2955 C++17 this function was in <utility> and used std::error_code moved to <charconv> and uses std::errc LWG 3266 C++17 bool argument was accepted and promoted to int rejected by a deleted overload LWG 3373 C++17 std::to_chars_result might have additional members additional members are disallowed [edit] See also

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