ISALPHA(3) BSD Programmer's Manual ISALPHA(3)
isalpha - alphabetic character test
#include <ctype.h> int isalpha(int c);
The isalpha() function tests for any character for which isupper(3) or islower(3) is true and for which none of iscntrl(3), isdigit(3), ispunct(3), or isspace(3) is true. In the C locale, isalpha() returns true only for the characters for which isupper(3) or islower(3) is true.
The isalpha() macro returns zero if the character tests false or non-zero if the character tests true.
isalnum(3), isascii(3), isblank(3), iscntrl(3), isdigit(3), isgraph(3), islower(3), isprint(3), ispunct(3), isspace(3), isupper(3), isxdigit(3), stdio(3), toascii(3), tolower(3), toupper(3), ascii(7)
The isalpha() function conforms to ANSI X3.159-1989 ("ANSI C89").
The argument to isalpha() must be EOF or representable as an unsigned char; otherwise, the result is undefined. MirBSD #10-current June 29, 1991 1