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

       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 plus or minus sign, then one of
       the following:

        * A non-empty sequence of decimal digits optionally containing a radix character, then an
          optional exponent part

        * A  0x  or  0X,  then a non-empty sequence of hexadecimal digits optionally containing a
          radix character, then an optional binary exponent part

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

        * One of NAN or NAN(n-wchar-sequence_opt), 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 minus sign, 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-sequence_opt)  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 program's 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.

       The wcstod() function 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 "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

       iswspace() , localeconv() , scanf() , setlocale() , wcstol() , the Base Definitions volume
       of IEEE Std 1003.1-2001, Chapter 7, Locale, <float.h>, <wchar.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  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 .