# wcstod

## 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 *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 **"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.
    


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