ISALPHA Section: Linux Programmer's Manual (3) Updated: September 2, 2025 Index   NAME isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit - character classification routines   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 check whether c, which must have the value of an unsigned char or EOF, falls into a certain character class according to the current locale. isalnum() checks for an alphanumeric character; it is equivalent to (isalpha(c) || isdigit(c)). isalpha() checks for an alphabetic character; in the standard "C" locale, it is equivalent to (isupper(c) || islower(c)). In some locales, there may be additional characters for which isalpha() is true--letters which are neither upper case nor lower case. isascii() checks whether c is a 7-bit unsigned char value that fits into the ASCII character set. This function is a BSD extension and is also an SVID extension. isblank() checks for a blank character; that is, a space or a tab. This function is a GNU extension. iscntrl() checks for a control character. isdigit() checks for a digit (0 through 9). isgraph() checks for any printable character except space. islower() checks for a lower-case character. isprint() checks for any printable character including space. ispunct() checks for any printable character which is not a space or an alphanumeric character. isspace() checks for white-space characters. In the C and POSIX locales, these are: space, form-feed ('\f'), newline ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). isupper() checks for an uppercase letter. isxdigit() checks for a hexadecimal digits, i.e. one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.   RETURN VALUE The values returned are nonzero if the character c falls into the tested class, and a zero value if not.   CONFORMING TO ANSI - C, BSD 4.3. isascii() is a BSD extension and is also an SVID extension. isblank() is a GNU extension.   NOTE The details of what characters belong into which class depend on the current locale. For example, isupper() will not recognize an A - umlaut as an uppercase letter in the default C locale.   SEE ALSO   Index NAME SYNOPSIS DESCRIPTION RETURN VALUE CONFORMING TO NOTE SEE ALSO This document was created by using the manual pages. Time: 11:58:04 GMT, March 24, 2025