ctype(3C)

NAME

ctype: isalnum(), isalpha(), isascii(), isblank(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit() — classify characters according to type

SYNOPSIS

#include <ctype.h>

int isalnum(int c);
int isalpha(int c);
int isascii(int c);
int isblank(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);

DESCRIPTION

These functions classify character-coded integer values according to the rules of the coded character set identified by the last successful call to setlocale() (see setlocale(3C)). Each function is a predicate returning nonzero for true, zero for false.

If setlocale() has not been called successfully, characters are classified according to the rules of the default ASCII 7-bit coded character set (see setlocale(3C)).

isascii() is defined on all integer values; the other functions are defined for the range -1 (EOF) through 255.

RETURN VALUE

The functions return nonzero under the following circumstances; zero otherwise:

isalnum(c): c is an alphanumeric (letters or digits).
isalpha(c): c is a letter.
isascii(c): c is any ASCII character code between 0 and 0177, inclusive.
isblank(c): c is a blank character; that is, a space or a tab.
iscntrl(c): c is a control character (in ASCII: character codes less than 040 and the delete character (0177)).
isdigit(c): c is a decimal digit (in ASCII: characters [0-9]).
isgraph(c): c is a visible character (in ASCII: printing characters, excluding the space character (040)).
islower(c): c is a lowercase letter.
isprint(c): c is a printing character.
ispunct(c): c is a punctuation character (in ASCII: any printing character except the space character (040), digits, letters).
isspace(c): c is a character that creates whitespace in displayed text (in ASCII: space, tab, carriage return, newline, vertical tab, and formfeed).
isupper(c): c is an uppercase letter.
isxdigit(c): c is a hexadecimal digit (in ASCII: characters [0-9], [A-F] or [a-f]).

If the argument to any of these functions is outside the domain of the function, the result is undefined.

EXTERNAL INFLUENCES

Environment Variables

The LC_CTYPE category determines the classification of character type.

International Code Set Support

Single-byte character code sets are supported.

WARNINGS

These functions are supplied both as library functions and as macros defined in the <ctype.h> header. Normally, the macro versions are used. To obtain the library function, either use a #undef to remove the macro definition or, if compiling in ANSI-C mode, enclose the function name in parenthesis or take its address. The following example uses the library functions for isalpha(), isdigit(), and isspace():

#include <ctype.h> 
#undef isalpha 
       ...
main() 
{ 
    int (*ctype_func)(); 
       ...
    if ( isalpha(c) ) 
       ...
    if ( (isdigit)(c) ) 
       ...
    ctype_func = isspace; 
       ...
} 

AUTHOR

ctype() was developed by IBM, OSF, and HP.

STANDARDS CONFORMANCE

isalnum(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isalpha(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isascii(): AES, SVID2, SVID3, XPG2, XPG3, XPG4

isblank(): ISO/IEC 9899:1999 (C99), UNIX 03

iscntrl(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isdigit(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isgraph(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

islower(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isprint(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

ispunct(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isspace(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isupper(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

isxdigit(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C