isalnum

Character classification macro.

Defined in header <ctype.h>

Syntax

#include <ctype.h>
int isalnum(int c);

Portability

Remarks

isalnum is a macro that classifies ASCII-coded integer values by table lookup. It is a predicate returning nonzero for true and 0 for false. It is defined only when isascii(c) is true or c is EOF.

You can make this macro available as a function by undefining (#undef) it.

Return value

isalnum returns nonzero if c is a letter (A to Z or a to 2) or a digit (0 to 9).

Example

*include <ctype.h>
#include <stdio.h>
int main(void)
{
   char c = 'C';
   if (isalnum(c))
      printf{"%c is alphanumeric\n" ,c);
   else
      printf("%c isn't alphanumeric\n" ,c);
   return 0;

Differences from modern implementations

Nothing recorded yet.

Modern references

• cppreference (search)
• POSIX (search)
• Microsoft C runtime (search)

These are search links, not yet checked by hand.

Stable link: /3.1/ctype.h/isalnum/ · short form /3.1/isalnum/