What is Signal?

Signals are the interrupts delivered to a process by the operating system which can Possibly terminate Our program prematurely. We can generate an interrupt by pressing Ctrl+C on the variety of the operating systems such as LINUX, UNIX, Mac OS X or Windows system. Signals are of various types; some could be caught by the program, and some not. Let’s see the list of the signals we can catch in the program and can perform the valid actions based on the signal. to handle signal in c++, we need to include < csignal > header file:

Signal() Function:

The signal() function is provided by the C++ signal-handling library for the purpose to trap the unexpected and unwanted events. Let’s check the general form of the signal() function:

void (*signal (int sig, void (*func)(int)))(int);

This function need two arguments. The integer argument specifies the signal number and the pointer argument specifies the signal-handling function.

Let's have an simple example, where we will catch an signal Interrupt (SIGINT) signal using Signal() function. Whatever signal we want to catch in our program, we must register that signal using Signal function and associate it with a signal handler.

/*Example: Signal Handling: InfoBrother:*/
 
#include <iostream>
#include <csignal>//required for signal Handling:
 
using namespace std;
 
void signalHandler( int signum )
{
   cout << "Interrupt signal (" << signum << ") received.\n";
 
   // cleanup and close up stuff here 
   // terminate program 
 
   exit(signum); 
}
 
main () 
{
   // register signal SIGINT and signal handler 
   signal(SIGINT, signalHandler); 
 
   while(1)
   {
      cout << "Sleeping...." << endl;
      sleep(1);
   }
 
   return 0;
}

When we compile and execute our Program, it work Normally. then we press Ctrl+C to interrupt the execution of program. our program catch the signal and came out of the loop.

raise() Function

We can generate Signals by the raise() functions. This function need an argument, which is an integer signal number.

int raise (signal sig);

Here, sig is the signal number to send any of the signals: SIGINT, SIGABRT, SIGFPE, SIGILL, SIGSEGV, SIGTERM, SIGHUP. Following is the example where we raise a signal internally using raise() function as follows:

/*Example: raise() Function : InfoBrother*/
 
#include <iostream>
#include <csignal>//required for signal handling:
 
using namespace std;
 
void signalHandler( int signum ) 
{
   cout << "Interrupt signal (" << signum << ") received.\n";
 
   // cleanup and close up stuff here 
   // terminate program 
 
   exit(signum); 
}
 
main () 
{
   int i = 0;
   // register signal SIGINT and signal handler 
   signal(SIGINT, signalHandler); 
 
   while(++i)
   {
      cout << "Sleeping...." << endl;
 
      if( i == 3 )
      {
         raise( SIGINT);
      }
 
      sleep(1);
   }
 
   return 0;
}