3.1 isalnum—alphanumeric character predicate

Synopsis

     #include <ctype.h>
     int isalnum(int c);
     

Description
isalnum is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero for alphabetic or numeric ASCII characters, and 0 for other arguments. It is defined only if c is representable as an unsigned char or if c is EOF.

You can use a compiled subroutine instead of the macro definition by undefining the macro using `#undef isalnum'.

Returns
isalnum returns non-zero if c is a letter (a–z or A–Z) or a digit (0–9).

Portability
isalnum is ANSI C.

No OS subroutines are required.