isalnum, isalpha, isascii, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit - Classify characters
Standard C Library (libc.so, libc.a)
Interfaces documented on this reference page conform to industry standards as follows:
isalnum(), isalpha(), isascii(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit(): XPG4, XPG4-UNIX
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:
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.
[Digital] 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.
Functions: ctype(3), setlocale(3), wctype(3)
Standards: i18n_intro(5), standards(5) delim off