How to Catch a Ctrl-C Event

How can I catch a ctrl-c event?

signal isn't the most reliable way as it differs in implementations. I would recommend using sigaction. Tom's code would now look like this :

#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

void my_handler(int s){
           printf("Caught signal %d\n",s);
           exit(1); 

}

int main(int argc,char** argv)
{

   struct sigaction sigIntHandler;

   sigIntHandler.sa_handler = my_handler;
   sigemptyset(&sigIntHandler.sa_mask);
   sigIntHandler.sa_flags = 0;

   sigaction(SIGINT, &sigIntHandler, NULL);

   pause();

   return 0;    
}

Ctrl + C interrupt event handling in Linux

When you press Ctr + C, the operating system sends a signal to the process. There are many signals and one of them is SIGINT. The SIGINT ("program interrupt") is one of the Termination Signals.

There are a few more kinds of Termination Signals, but the interesting thing about SIGINT is that it can be handled (caught) by your program. The default action of SIGINT is program termination. That is, if your program doesn't specifically handle this signal, when you press Ctr + C your program terminates as the default action.

To change the default action of a signal you have to register the signal to be caught. To register a signal in a C program (at least under POSIX systems) there are two functions

1. signal(int signum, sighandler_t handler);
2. sigaction(int signum, const struct sigaction *act,
   struct sigaction *oldact);.

These functions require the header signal.h to be included in your C code. I have provide a simple example of the signal function below with comments.

#include <stdio.h>
#include <stdlib.h>
#include <signal.h> //  our new library 
volatile sig_atomic_t flag = 0;
void my_function(int sig){ // can be called asynchronously
  flag = 1; // set flag
}

int main(){
  // Register signals 
  signal(SIGINT, my_function); 
  //      ^          ^
  //  Which-Signal   |-- which user defined function registered
  while(1)  
    if(flag){ // my action when signal set it 1
        printf("\n Signal caught!\n");
        printf("\n default action it not termination!\n");
        flag = 0;
    }     
  return 0;
}  

Note: you should only call safe/authorized functions in signal handler. For example avoid calling printf in signal handler.

You can compile this code with gcc and execute it from the shell. There is an infinite loop in the code and it will run until you send a SIGINT signal by pressing Ctr + C.

Catching ctrl+c event in console application (multi-threaded)

Based on your question there are two events you need to catch.

• First there is the console close event which is explained here: "On Exit" for a Console Application
• Second you want to catch control c which is explained here: How do I trap ctrl-c in a C# console app

If you put these two together with your example you get something like this:

static ConsoleEventDelegate handler;
private delegate bool ConsoleEventDelegate(int eventType);
[DllImport("kernel32.dll", SetLastError = true)]
private static extern bool SetConsoleCtrlHandler(ConsoleEventDelegate callback, bool add);

private static MyExternalProcess p1;

public static void Main()
{
    Console.CancelKeyPress += delegate
    {
        killEveryoneOnExit();
    };

    handler = new ConsoleEventDelegate(ConsoleEventCallback);
    SetConsoleCtrlHandler(handler, true);

    p1 = new MyExternalProcess();
    p1.startProcess();
}

public static void killEveryoneOnExit()
{
    p1.kill();
}

static bool ConsoleEventCallback(int eventType)
{
    if (eventType == 2)
    {
        killEveryoneOnExit();
    }
    return false;
}

For a working ctrl c (fun intended) paste example: http://pastebin.com/6VV4JKPY

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