isalnum—alphanumeric character predicate #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.