isdigit

Character classification macro.

Defined in header <ctype.h>

Syntax

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

isdigit 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 isEOF.

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

Portability

Return value

isdigit returns nonzero if c is a digit (0 to 9).

Example

#include <ctype.h>
#include <stdio.h>

int main(void)
{
   char c = 'C ;
   if (isdigit(c))
      printf("%c is a digit\n",c);
   else
      printf("%c isn't a digit\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/isdigit/ · short form /3.1/isdigit/