How can i use sigaction() to intercept SIGINT? - c++

Question

I am trying to modify the following code to use sigaction() to intercept SIGINT;
I need to replace the "for" loop with "while ( 1 ); you should be able to quit the program by entering "^\". (Need to intercept SIGQUIT.)
#include <signal.h>
#include <unistd.h>
#include <iostream>
using namespace std;
void func ( int sig )
{
cout << "Oops! -- I got a signal " << sig << endl;
}
int main()
{
(void) signal ( SIGINT, func ); //catch terminal interrupts
//for ( int i = 0; i < 20; ++i )
while(1)
{
cout << "signals" << endl;
sleep ( 1 );
}
return 0;
}

Answer 1

You can use sigaction to catch SIGINT (and still have the output you've described) with the following code (which compiles and works for me using clang on a Unix like OS):
#include <signal.h>
#include <iostream>
#include <unistd.h>
static int sigcaught = 0;
static void sighandler(int signum)
{
sigcaught = signum;
}
int main()
{
int signum = SIGINT;
struct sigaction newact;
struct sigaction oldact;
newact.sa_handler = sighandler;
sigemptyset(&newact.sa_mask);
newact.sa_flags = 0;
sigaction(signum, &newact, &oldact);
while (!sigcaught)
{
std::cout << "waiting for signal" << std::endl;
sleep(1);
}
std::cout << "Oops! -- I got a signal " << sigcaught << std::endl;
return 0;
}
Please note that: this code intentionally isn't checking return values (like from sigaction nor sleep) since the original code isn't and since checking them may detract a reader from seeing the relevant differences. I would not want production code to ignore return values however (particularly those that can indicate errors).