WCSTOD(3)                  POSIX Programmer's Manual                 WCSTOD(3)



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

NAME
       wcstod, wcstof, wcstold -- convert a wide-character string to a double-
       precision number

SYNOPSIS
       #include <wchar.h>

       double wcstod(const wchar_t *restrict nptr, wchar_t **restrict endptr);
       float wcstof(const wchar_t *restrict nptr, wchar_t **restrict endptr);
       long double wcstold(const wchar_t *restrict nptr,
           wchar_t **restrict endptr);

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.1-2017
       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

       Then they shall 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 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:
                   digit
                   nondigit
                   n-wchar-sequence digit
                   n-wchar-sequence nondigit

       The subject sequence is defined as the longest initial subsequence of
       the input wide string, starting with the first non-white-space wide
       character, that is of the expected form. The subject sequence contains
       no wide characters if the input wide string is not of the expected
       form.

       If the subject sequence has the expected form for a floating-point
       number, the sequence of wide characters starting with the first digit
       or the radix character (whichever occurs first) shall be interpreted as
       a floating constant according to the rules of the C language, except
       that the radix character shall be used in place of a period, and that
       if neither an exponent part nor a radix character appears in a decimal
       floating-point number, or if a binary exponent part does not appear in
       a hexadecimal floating-point number, an exponent part of the
       appropriate type with value zero shall be assumed to follow the last
       digit in the string. If the subject sequence begins with a <hyphen-
       minus>, the sequence shall be interpreted as negated. A wide-character
       sequence INF or INFINITY shall be interpreted as an infinity, if
       representable in the return type, else as if it were a floating
       constant that is too large for the range of the return type. A wide-
       character sequence NAN or NAN(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 locale, additional locale-specific subject
       sequence forms 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.

       The 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 ""LL<=DD<=UU"".  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(), wcstol()

       The Base Definitions volume of POSIX.1-2017, Chapter _7, Locale,
       <float.h>, <wchar.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            WCSTOD(3)
