ctype(3)ctype(3)NAME
isalnum, isalpha, isascii, iscntrl, isdigit, isgraph, islower, isprint,
ispunct, isspace, isupper, isxdigit - Classify characters
SYNOPSIS
#include <ctype.h>
int isalnum(
int c ); int isalpha(
int c ); int isascii(
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 );
LIBRARY
Standard C Library (libc)
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
isalnum(), isalpha(), isascii(), iscntrl(), isdigit(), isgraph(),
islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit():
XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Specifies the character to be tested. In all cases, this parameter is
an int data type, whose value must be representable as an unsigned char
or must equal the value of the macro EOF (defined in the stdio.h
include file). When this parameter has a value that cannot be repre‐
sented as an unsigned char or EOF, the result is undefined.
DESCRIPTION
The ctype functions test for membership in a character class in the
current locale. Each function tests to see if a character is part of a
different character class.
If the character is part of the character class, the function returns a
nonzero value for true; otherwise, the function returns a value of 0
(zero) for false.
Each function is named by adding the prefix is to the name of the char‐
acter class for which the function tests. For example, the isalpha()
function tests whether the character specified by the c parameter
belongs to the alpha class.
The following lists the function names and describes the conditions
under which the functions return a true value. When c is a character
of class alpha or class digit in the program's current locale. When c
is a character of class alpha in the program's current locale. Charac‐
ters in classes lower and upper automatically belong to class alpha.
When c is a 7-bit US-ASCII character whose value is in the range 0 to
0177 (0 to 0x7F), inclusive. When c is a character of class cntrl in
the program's current locale. When c is a character of class digit in
the program's current locale. The following characters are included in
this class:
0 1 2 3 4 5 6 7 8 9 When c is a character of class graph in the
program's current locale. Characters in classes alpha, digit,
and punct are automatically in class graph. Unlike isprint(),
isgraph() returns FALSE for the space character. When c is a
character of class lower in the program's current locale. At a
minimum, the 26 lowercase US-ASCII characters are included in
this class. These are:
a b c d e f g h i j k l m n o p q r s t u v w x y z When c is a
character of class print in the program's current locale. All
characters in the class graph and the space character are auto‐
matically included in the class print. When c is a character of
class punct in the program's current locale. When c is a char‐
acter of class space in the program's current locale. At a mini‐
mum, the space, form-feed, newline, carriage-return, tab, and
vertical-tab characters are included in this class. When c is a
character of class upper in the program's current locale. At a
minimum, the 26 uppercase US-ASCII characters are included in
this class. These are:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z When c is a
character of class xdigit in the program's current locale. The
following characters are included in this class:
0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f
NOTES
The LC_CTYPE category of the current locale affects all conversions.
In the C locale, or in a locale where character-type information is not
defined, characters are classified according to the rules of the ASCII
character set. For any character value greater than octal 177 (0177 in
C-language context) the value 0 (zero) is returned.
[Tru64 UNIX] The isdigit(), isxdigit(), and isalnum() functions do not
recognize Thai digits. Many applications make assumptions about how a
digit character can be converted to its numeric equivalent. Changing
the functions to recognize Thai digits would break these applications.
Refer to TACTIS(5) for more information about Thai digits.
RETURN VALUES
Upon successful completion of any function, a nonzero (TRUE) value is
returned. Otherwise, the value 0 (FALSE) is returned.
SEE ALSO
Files: locale(4)
Functions: ctype(3), setlocale(3), wctype(3)
Standards: i18n_intro(5), standards(5)ctype(3)
