stold

Stold is the C++ standard library function std::stold used to convert a string to a long double value. It is part of the numeric conversion utilities introduced in C++11 and is declared in the <string> header. The function operates within the std namespace and provides overloads for both std::string and std::wstring inputs, with an optional index parameter to report how many characters were processed.

Signature and overloads

- long double stold(const std::string& str, std::size_t* idx = 0);

- long double stold(const std::wstring& str, std::size_t* idx = 0);

The idx parameter, if non-null, is set to the number of characters used in the conversion. There is no overload for C-style strings in the C++ std::stold family; conversions from C strings are typically done via std::strtold in C or by first constructing a std::string.

Behavior and error handling

std::stold throws exceptions to signal errors:

- std::invalid_argument if no conversion could be performed from the input string.

- std::out_of_range if the converted value is outside the representable range of long double.

The conversion is locale-sensitive, so the current locale can influence parsing in terms of decimal separators and numeric formatting.

Relationship to C equivalents

In C, the analogous conversion function is strtold, which accepts a C string and reports the position of the first unprocessed character via an endptr. The C and C++ facilities share the concept of converting textual representations to floating-point values, but std::stold provides a type-safe, exception-based C++ interface.

Notes

The actual precision and range of long double depend on the platform and compiler; on some systems long double may be the same as double. As with other std::stof/stod/stold family functions, conversions can be affected by locale settings and may yield implementation-defined results in edge cases.