"Safely" terminate a running C++ program on keypress? - c++

Question

I'm trying to write a simulation that will carry on running until I press a certain key (like 'q' for quit). Then after I press that, I want the program to finish writing the data its currently writing, close files, then gracefully exit (as opposed to just pressing ctrl+c to force the program to stop). Is there any way to do this on C++?
Thanks

Answer 1

Have the user press CTRL-C, but install a signal handler to deal with it. In the signal handler, set a global boolean variable, for example user_wants_to_quit. Then your sim loop can look like:
while ( work_to_be_done && !user_wants_to_quit) {
…
}
// Loop exited, clean up my data
A complete POSIX program (sorry, if you were hoping for Microsoft Windows), including setting and restoring the SIGINT (CTRL-C) handler:
#include <iostream>
#include <signal.h>
namespace {
sig_atomic_t user_wants_to_quit = 0;
void signal_handler(int) {
user_wants_to_quit = 1;
}
}
int main () {
// Install signal handler
struct sigaction act;
struct sigaction oldact;
act.sa_handler = signal_handler;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
sigaction(SIGINT, &act, &oldact);
// Run the sim loop
int sim_loop_counter = 3;
while( (sim_loop_counter--) && !user_wants_to_quit) {
std::cout << "Running sim step " << sim_loop_counter << std::endl;
// Sim logic goes here. I'll substitute a sleep() for the actual
// sim logic
sleep(1);
std::cout << "Step #" << sim_loop_counter << " is now complete." << std::endl;
}
// Restore old signal handler [optional]
sigaction(SIGINT, &oldact, 0);
if( user_wants_to_quit ) {
std::cout << "SIM aborted\n";
} else {
std::cout << "SIM complete\n";
}
}