std::to_chars - cppreference.com (original) (raw)

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 or 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.

1. 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[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 #include #include #include #include   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.

[edit] See also