isalnum

int isalnum( int ch );

Checks if the given character is an alphanumeric character as classified by the current C locale. In the default locale, the following characters are alphanumeric:

• digits (0123456789)
• uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
• lowercase letters (abcdefghijklmnopqrstuvwxyz)

The behavior is undefined if the value of ch is not representable as unsigned char and is not equal to EOF.

Parameters

Return value

Non-zero value if the character is an alphanumeric character, 0 otherwise.

Example

#include <stdio.h>
#include <ctype.h>
#include <locale.h>
 
int main(void)
{
    unsigned char c = '\xdf'; // German letter ß in ISO-8859-1
 
    printf("isalnum('\\xdf') in default C locale returned %d\n", !!isalnum(c));
 
    setlocale(LC_CTYPE, "de_DE.iso88591");
    printf("isalnum('\\xdf') in ISO-8859-1 locale returned %d\n", !!isalnum(c));
}

isalnum('\xdf') in default C locale returned 0
isalnum('\xdf') in ISO-8859-1 locale returned 1

References

• C11 standard (ISO/IEC 9899:2011):
  • 7.4.1.1 The isalnum function (p: 200)
• C99 standard (ISO/IEC 9899:1999):
  • 7.4.1.1 The isalnum function (p: 181)
• C89/C90 standard (ISO/IEC 9899:1990):
  • 4.3.1.1 The isalnum function

See also