Signal Handling in C++

C++Server Side ProgrammingProgramming

Signals are the interrupts delivered to a process by the operating system which can terminate a program prematurely. You can generate interrupts by pressing Ctrl+C on a UNIX, LINUX, Mac OS X or Windows system.

There are signals which cannot be caught by the program but there is a following list of signals which you can catch in your program and can take appropriate actions based on the signal. These signals are defined in C++ header file

Signal
Description
SIGABRT
Abnormal termination of the program, such as a call to abort.
SIGFPE
An erroneous arithmetic operation, such as a divide by zero or an operation resulting in overflow.
SIGILL
Detection of an illegal instruction.
SIGINT
Receipt of an interactive attention signal.
SIGSEGV
An invalid access to storage.
SIGTERM
A termination request sent to the program.

The signal() Function

C++ signal-handling library provides function signal to trap unexpected events. Following is the syntax of the signal() function −

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

Keeping it simple, this function receives two arguments: first argument as an integer which represents signal number and second argument as a pointer to the signal-handling function.

Let us write a simple C++ program where we will catch SIGINT signal using signal() function. Whatever signal you want to catch in your program, you must register that signal using signal function and associate it with a signal handler. Examine the following example −

Example

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

Output

Going to sleep....
Going to sleep....
Going to sleep....

After pressing Ctrl + C, it will show,

Output

Going to sleep....
Going to sleep....
Going to sleep....
Interrupt signal (2) received.

The raise() Function

You can generate signals by function raise(), which takes an integer signal number as an argument and has the following syntax.

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

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

Output

Going to sleep....
Going to sleep....
Going to sleep....
Interrupt signal (2) received.
raja
Published on 29-Apr-2019 13:12:45
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