isalnum(3) -- Linux man page
NAMEisalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit - character classification routines
#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);
DESCRIPTIONThese 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.
- checks for an alphanumeric character; it is equivalent to (isalpha(c) || isdigit(c)).
- 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.
- 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.
- checks for a blank character; that is, a space or a tab. This function is a GNU extension.
- checks for a control character.
- checks for a digit (0 through 9).
- checks for any printable character except space.
- checks for a lower-case character.
- checks for any printable character including space.
- checks for any printable character which is not a space or an alphanumeric character.
- 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').
- checks for an uppercase letter.
- 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 VALUEThe values returned are nonzero if the character c falls into the tested class, and a zero value if not.
CONFORMING TOANSI - C, BSD 4.3. isascii() is a BSD extension and is also an SVID extension. isblank() is a GNU extension.
NOTEThe 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 ALSOtolower(3), toupper(3), setlocale(3), ascii(7), locale(7)