# wcstod (3p)

# PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.# NAME

wcstod, wcstof, wcstold — convert a wide-character string to a double-precision number# SYNOPSIS

#include <wchar.h>

double wcstod(const wchar_t *restrictnptr, wchar_t **restrictendptr); float wcstof(const wchar_t *restrictnptr, wchar_t **restrictendptr); long double wcstold(const wchar_t *restrictnptr, wchar_t **restrictendptr);

# DESCRIPTION

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard. These functions shall convert the initial portion of the wide-character string pointed to by*nptr*to

**double**,

**float**, and

**long double**representation, respectively. First, they shall decompose the input wide-character string into three parts:

- 1.
- An initial, possibly empty, sequence of white-space wide-character codes (as specified by
*iswspace*())

- 2.
- A subject sequence interpreted as a floating-point constant or representing infinity or NaN

- 3.
- A final wide-character string of one or more unrecognized wide-character codes, including the terminating null wide-character code of the input wide-character string

**'+'**or

**'−'**sign, then one of the following:

- *
- A non-empty sequence of decimal digits optionally containing a radix character; then an optional exponent part consisting of the wide character
**'e'**or the wide character**'E'**, optionally followed by a**'+'**or**'−'**wide character, and then followed by one or more decimal digits

- *
- A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally containing a radix character; then an optional binary exponent part consisting of the wide character
**'p'**or the wide character**'P'**, optionally followed by a**'+'**or**'−'**wide character, and then followed by one or more decimal digits

- *
- One of INF or INFINITY, or any other wide string equivalent except for case

- *
- One of NAN or NAN(
*n-wchar-sequenceopt*), or any other wide string ignoring case in the NAN part, where:

n-wchar-sequence:digitnondigitn-wchar-sequence digitn-wchar-sequence nondigit

*n-wchar-sequenceopt*) shall be interpreted as a quiet NaN, if supported in the return type, else as if it were a subject sequence part that does not have the expected form; the meaning of the

*n*-wchar sequences is implementation-defined. A pointer to the final wide string shall be stored in the object pointed to by

*endptr*, provided that

*endptr*is not a null pointer. If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the conversion shall be rounded in an implementation-defined manner. The radix character shall be as defined in the current locale (category

*LC_NUMERIC*). In the POSIX locale, or in a locale where the radix character is not defined, the radix character shall default to a <period> (

**'.'**). In other than the C or POSIX locales, other implementation-defined subject sequences may be accepted. If the subject sequence is empty or does not have the expected form, no conversion shall be performed; the value of

*nptr*shall be stored in the object pointed to by

*endptr*, provided that

*endptr*is not a null pointer. These functions shall not change the setting of

*errno*if successful. Since 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, then call

*wcstod*(),

*wcstof*(), or

*wcstold*(), then check

*errno*.

# RETURN VALUE

Upon successful completion, these functions shall return the converted value. If no conversion could be performed, 0 shall be returned and*errno*may be set to

**[EINVAL]**. If the correct value is outside the range of representable values, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL shall be returned (according to the sign of the value), and

*errno*shall be set to

**[ERANGE]**. If the correct value would cause underflow, a value whose magnitude is no greater than the smallest normalized positive number in the return type shall be returned and

*errno*set to

**[ERANGE]**.

# ERRORS

The*wcstod*() function shall fail if:

**ERANGE**- The value to be returned would cause overflow or underflow.

*wcstod*() function may fail if:

**EINVAL**- No conversion could be performed.

*The following sections are informative.*

# EXAMPLES

None.# APPLICATION USAGE

If the subject sequence has the hexadecimal form and FLT_RADIX is not a power of 2, and the result is not exactly representable, the result should be one of the two numbers in the appropriate internal format that are adjacent to the hexadecimal floating source value, with the extra stipulation that the error should have a correct sign for the current rounding direction. If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in*<float.h>*) significant digits, the result should be correctly rounded. If the subject sequence

*D*has the decimal form and more than DECIMAL_DIG significant digits, consider the two bounding, adjacent decimal strings

*L*and

*U*, both having DECIMAL_DIG significant digits, such that the values of

*L*,

*D*, and

*U*satisfy

**"L**<=

**D**<=

**U"**. The result should be one of the (equal or adjacent) values that would be obtained by correctly rounding

*L*and

*U*according to the current rounding direction, with the extra stipulation that the error with respect to

*D*should have a correct sign for the current rounding direction.

# RATIONALE

None.# FUTURE DIRECTIONS

None.# SEE ALSO

*,*

*fscanf*()*,*

*iswspace*()*,*

*localeconv*()*,*

*setlocale*()*The Base Definitions volume of POSIX.1‐2008,*

*wcstol*()*Chapter 7*,

*Locale*,

*,*

**<float.h>**

**<wchar.h>**