CTYPE(3) — C LIBRARY FUNCTIONS

NAME

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

SYNOPSIS

#include <ctype.h>

isalpha(c)

...

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 is defined on all integer values; the rest are defined only where isascii(c) is true and on the single non-ASCII value EOF (see stdio(3S)).

isalpha(c) c is a letter

isupper(c) c is an upper case letter

islower(c) c is a lower case letter

isdigit(c) c is a digit [0-9].

isxdigit(c) c is a hexadecimal digit [0-9], [A-F], or [a-f].

isalnum(c)
c is an alphanumeric character, that is, c is a letter or a digit

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

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

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

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

isascii(c) c is an ASCII character, code less than 0200

isgraph(c) c is a visible graphic character, code 041 (exclamation mark) through 0176 (tilde).

CHARACTER CONVERSION MACROS

These macros perform simple conversions on single characters.

toupper(c) converts c to its upper-case equivalent. Note that this only works where c is known to be a lower-case character to start with (presumably checked via islower).

tolower(c) converts c to its lower-case equivalent. Note that this only works where c is known to be a upper-case character to start with (presumably checked via isupper).

toascii(c) masks c with the correct value so that c is guaranteed to be an ASCII character in the range 0 thru 0x7f.

DIAGNOSTICS

If the argument to any of these macros is not in the domain of the function, the result is undefined.

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