The iswdigit() function shall test whether wc is a wide-character
code representing a character of class digit in the program's current
locale; see the Base Definitions volume of IEEE Std 1003.1-2001,
Chapter 7, Locale.
The wc argument is a wint_t, the value of which the application
shall ensure is a wide-character code corresponding to a valid character in
the current locale, or equal to the value of the macro WEOF. If the argument
has any other value, the behavior is undefined.
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