16.1.4.7 c-strtold

The c-strtold module contains a string to number (‘long double’) conversion function operating on single-byte character strings, that operates as if the locale encoding was ASCII. (The "C" locale on many systems has the locale encoding "ASCII".)

The function is:

extern long double c_strtold (const char *string, char **endp);

In particular, only a period ‘.’ is accepted as decimal point, even when the current locale’s notion of decimal point is a comma ‘,’.