The wcstod() and wstod() functions convert the initial portion of the wide character string pointed to by nptr to double representation. They first decompose the input wide character string into three parts: an initial, possibly empty, sequence of white-space wide character codes (as specified by iswspace(3C)); a subject sequence interpreted as a floating-point constant; and a final wide-character string of one or more unrecognised wide-character codes, including the terminating null wide character code of the input wide character string. They then attempt to convert the subject sequence to a floating-point number, and return the result.

The expected form of the subject sequence is an optional `+' or `-' sign, then a non-empty sequence of digits optionally containing a radix, then an optional exponent part. An exponent part consists of `e' or `E', followed by an optional sign, followed by one or more decimal digits. The subject sequence is defined as the longest initial subsequence of the input wide character string, starting with the first non-white-space wide-character code, that is of the expected form. The subject sequence contains no wide-character codes if the input wide character string is empty or consists entirely of white-space wide-character codes, or if the first wide-character code that is not white space other than a sign, a digit or a radix.

If the subject sequence has the expected form, the sequence of wide-character codes starting with the first digit or the radix (whichever occurs first) is interpreted as a floating constant as defined in the C language, except that the radix is used in place of a period, and that if neither an exponent part nor a radix appears, a radix is assumed to follow the last digit in the wide character string. If the subject sequence begins with a minus sign (-), the value resulting from the conversion is negated. A pointer to the final wide character string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.

The radix is defined in the program's locale (category LC_NUMERIC). In the POSIX locale, or in a locale where the radix is not defined, the radix defaults to a period (.).

In other than the POSIX locale, other implementation-dependent subject sequence forms may be accepted.

If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.

The watof(str) function is equivalent to wstod(str, (wchar_t **)NULL).

The wcstod() and wstod() functions return the converted value, if any. If no conversion could be performed, 0 is returned and errno may be set to EINVAL.

If the correct value is outside the range of representable values, +-HUGE_VAL is returned (according to the sign of the value), and errno is set to ERANGE.

If the correct value would cause underflow, 0 is returned, and errno is set to ERANGE.

The wcstod() and wstod() functions will fail if:

ERANGE

The value to be returned would cause overflow or underflow.

The wcstod() and wcstod() functions may fail if:

EINVAL

No conversion could be performed.

Because 0 is returned on error and is also a valid return on success, an application wishing to check for error situations should set errno to 0 call wcstod() or wstod(), then check errno and if it is non-zero, assume an error has occurred.

See attributes(5) for descriptions of the following attributes:

iswspace(3C), localeconv(3C), scanf(3C), setlocale(3C), wcstol(3C), attributes(5)