3.2 isalpha—alphabetic character predicate

Synopsis

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

Description
isalpha is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero when c represents an alphabetic ASCII character, and 0 otherwise. 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 isalpha'.

Returns
isalpha returns non-zero if c is a letter (A–Z or a–z).

Portability
isalpha is ANSI C.

No supporting OS subroutines are required.