ctype(S)

ctype -- character handling routines

Syntax

#include <ctype.h>

int isdigit(c);
int c;

 . . .
int isascii(c);
int c;

Description

The character classification macros listed below are defined by the <ctype.h> header file. They each return nonzero for true, zero for false.

These functions classify character-coded integer values according to the rules of the coded character set defined by character type information in the program's locale (category LC_TYPE).

In the C locale, or in a locale where character type information is not defined, characters are classified according to the rules of the US-ASCII 7-bit coded character set, returning zero for values above octal 0177.

In all cases the argument is an integer, the value of which must be representable as an unsigned char or must equal the value of the macro EOF. If the argument has any other value, the behavior is undefined. isascii is defined on all integer values.

isdigit: tests for the digits 0 through 9.
isxdigit: tests for any character for which isdigit is true or for the letters a through f or A through F.
islower: tests for any lowercase letter as defined by the character set.
isupper: tests for any uppercase letter as defined by the character set.
isalpha: tests for any character for which islower or isupper is true and possibly any others as defined by the character set.
isalnum: tests for any character for which isalpha or isdigit is true.
isspace: tests for a space, horizontal-tab, carriage return, newline, vertical-tab, or form-feed.
iscntrl: tests for ``control characters'' as defined by the character set.
ispunct: tests for any character other than the ones for which isalnum, iscntrl, or isspace is true.
isprint: tests for a space or any character for which isalnum or ispunct is true or other ``printing character'' as defined by the character set.
isgraph: tests for any character for which isprint is true, except for space.
isascii: tests for an ASCII character (a non-negative number less than 0200).

All the character classification macros do a table lookup.

Diagnostics

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

Warning

If a character variable or constant is passed to these functions or macros, undefined results may occur on machines which sign-extend characters by default.

Standards conformance

isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, and isxdigit are conformant with: