isalnum, isalpha, isascii, iscntrl, isdigit, isgraph,
islower, isprint, ispunct, isspace, isupper, isxdigit -
Classify characters
#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 );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards 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.
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 represented as
an unsigned char or EOF, the result is undefined.
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 character 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. Characters 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 automatically
included in the class print. When c is a character
of class punct in the program's current locale.
When c is a character of class space in the program's
current locale. At a minimum, 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
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.
Upon successful completion of any function, a nonzero
(TRUE) value is returned. Otherwise, the value 0 (FALSE)
is returned.
Files: locale(4)
Functions: ctype(3), setlocale(3), wctype(3)
Standards: i18n_intro(5), standards(5)
ctype(3)
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