NAME

isalnum, isalpha, isascii, iscntrl, isdigit, islower, isprint, ispunct, isspace, isupper, toascii, tolower, toupper − character classification and conversion macros

SYNOPSIS

#include <ctype.h>

isalnum(c)

. . . 

DESCRIPTION

The is∗ macros classify ASCII-coded integer values by table lookup.  Each is a predicate returning nonzero for true, zero for false.  Isascii is defined on all integer values; the rest are defined only where isascii is true and on the single non-ASCII value EOF (see stdio(3S)). If toupper is provided with a lower case letter (can be ensured by using isascii and islower both true) it will return an upper case ASCII character.  Input other than lower case results in undefined values.  If tolower is provided with an upper case letter (can be ensured by using isascii and isupper both true) it will return a lower-case ASCII character.  Input other than upper case results in undefined values.  No matter what value c has, toascii returns an ASCII character. 

These following macros return non-zero when c meets the indicated criteria:

isalnum c is an alphanumeric character

isalpha c is a letter

isascii c is an ASCII character, code less than 0200. 

iscntrl c is a delete character (0177) or ordinary control character (less than 040). 

isdigit c is a digit

islower c is a lower case letter

isprint c is a printing character, code 040(8) (space) through 0176 (tilde)

ispunct c is a punctuation character (neither control nor alphanumeric)

isspace c is a space, tab, carriage return, newline, or formfeed

isupper c is an upper case letter

SEE ALSO

ascii(7)

7th Edition