isalpha, isupper, islower, isdigit, isxdigit, isalnum, isspace, ispunct, isprint, isgraph,
iscntrl, isascii, toupper, tolower, toascii - character classification macros
. . .
These macros classify ASCII-coded integer values by table lookup. Each is a predicate
returning nonzero for true, zero for false. Isascii and toascii are defined on all inte-
ger values; the rest are defined only where isascii is true and on the single non-ASCII
value EOF (see stdio(3S)).
isalpha c is a letter
isupper c is an upper case letter
islower c is a lower case letter
isdigit c is a digit
isxdigit c is a hex digit
isalnum c is an alphanumeric character
isspace c is a space, tab, carriage return, newline, vertical tab, or formfeed
ispunct c is a punctuation character (neither control nor alphanumeric)
isprint c is a printing character, code 040(8) (space) through 0176 (tilde)
isgraph c is a printing character, similar to isprint except false for space.
iscntrl c is a delete character(0177) or ordinary control character (less than
isascii c is an ASCII character, code less than 0200
tolower c is converted to lower case. Return value is undefined if not isupper(c).
toupper c is converted to upper case. Return value is undefined if not islower(c).
toascii c is converted to be a valid ascii character.
7th Edition May 12, 1986 CTYPE(3)