Header File 

ctype.h  

Category 

Classification Routines 

Prototype 

int iscntrl(int c); 

int iswcntrl(wint_t c); 

Description 

Tests for a control character. 

iscntrl is a macro that classifies ASCII-coded integer values by table lookup. The macro is affected by the current locale’s LC_CTYPE category. For the default C locale, c is a delete character or control character (0x7F or 0x00 to 0x1F). 

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

Return Value 

iscntrl returns nonzero if c is a delete character or ordinary control character. 

Example  

#include <stdio.h>
#include <ctype.h>
int main(void)
{
  char c = 'C';
  if (iscntrl(c))
    printf("%c is a control character\n",c);
  else 
    printf("%c is not a control character\n",c);
  return 0;
}

Portability