int isalnum ( int c );

<cctype>

Check if character is alphanumeric

Checks if parameter c is either a decimal digit or an uppercase or lowercase letter.

The result is true if either isalpha or isdigit would also return true.

Notice that what is considered a letter may depend on the locale being used; In the default C locale, what constitutes a letter is what returns true by either isupper or islower.

For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.

Parameters

c

Character to be checked, casted as an int, or EOF.

Return Value

Example

/* isalnum example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i;
  char str[]="c3po...";
  i=0;
  while (isalnum(str[i])) i++;
  printf ("The first %d characters are alphanumeric.\n",i);
  return 0;
}

Output:

The first 4 characters are alphanumeric.

See also