isascii—ASCII character predicate #include <ctype.h>
int isascii(int c);
Description
isascii is a macro which returns non-zero when c is an ASCII
character, and 0 otherwise. It is defined for all integer values.
You can use a compiled subroutine instead of the macro definition by
undefining the macro using `#undef isascii'.
Returns
isascii returns non-zero if the low order byte of c is in the range
0 to 127 (0x00–0x7F).
Portability
isascii is ANSI C.
No supporting OS subroutines are required.