Write a C program that does not terminate when Ctrl+C is pressed

Difficulty Level : Hard
Last Updated : 16 Oct, 2019

Write a C program that doesn’t terminate when Ctrl+C is pressed. It prints a message “Cannot be terminated using Ctrl+c” and continues execution.

We can use signal handling in C for this. When Ctrl+C is pressed, SIGINT signal is generated, we can catch this signal and run our defined signal handler. C standard defines following 6 signals in signal.h header file.

SIGABRT – abnormal termination.
SIGFPE – floating point exception.
SIGILL – invalid instruction.
SIGINT – interactive attention request sent to the program.
SIGSEGV – invalid memory access.
SIGTERM – termination request sent to the program.

Additional signals are specified Unix and Unix-like operating systems (such as Linux) defines more than 15 additional signals. See http://en.wikipedia.org/wiki/Unix_signal#POSIX_signals
The standard C library function signal() can be used to set up a handler for any of the above signals.

/* A C program that does not terminate when Ctrl+C is pressed */
#include <stdio.h> 
#include <signal.h> 
  
/* Signal Handler for SIGINT */
void sigintHandler(int sig_num) 
{ 
    /* Reset handler to catch SIGINT next time. 
       Refer http://en.cppreference.com/w/c/program/signal */
    signal(SIGINT, sigintHandler); 
    printf("\n Cannot be terminated using Ctrl+C \n"); 
    fflush(stdout); 
} 
  
int main () 
{ 
    /* Set the SIGINT (Ctrl-C) signal handler to sigintHandler  
       Refer http://en.cppreference.com/w/c/program/signal */
    signal(SIGINT, sigintHandler); 
  
    /* Infinite loop */
    while(1) 
    {         
    } 
    return 0; 
} 

Output: When Ctrl+C was pressed two times

 
 Cannot be terminated using Ctrl+C
 
 Cannot be terminated using Ctrl+C

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