C++ Standard Library C++ STL Library

C++ <cctype> - iscntrl() Function

The C++ <cctype> iscntrl() function is used to check if the given character is a control character. A control character is a character that does not occupy a printing position on a display. In the default "C" locale, a control character are those between ASCII codes 0x00 (NUL) and 0x1f (US), plus 0x7f (DEL).

Other locales may consider a different selection of characters as control characters.


int iscntrl ( int ch );               


ch Specify the character to be checked, casted to an int, or EOF.

Return Value

Returns non-zero value (i.e, true) if ch is a control character, else returns zero (i.e, false).


The example below shows the usage of iscntrl() function.

#include <iostream>
#include <cctype>
using namespace std;
int main (){
  char str[50] = "Hello\nWorld!";

  //replacing all control 
  //characters with @ in str
  int i = 0;
  while(str[i]) {
      str[i] = '@';

  //displaying the output
  cout<<"str contains: "<<str;  
  return 0;

The output of the above code will be:

str contains: Hello@World!

❮ C++ <cctype> Library