The wcstold function converts the initial portion of the wide-character string pointed to by nptr to long double representation. First, this function decomposes the input string into three parts: an initial, possibly empty, sequence of white-space characters (as specified by the isspace function); a subject sequence resembling a floating-point constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, it attempts to convert the subject sequence to a floating-point number, and returns the result as a value of type float. The expected form of the (initial portion of the) wide string is optional leading white space, an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NaN (not-a-number).