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Signal Handling in C++

  • Difficulty Level : Medium
  • Last Updated : 07 Dec, 2021

Signals are the interrupts that force an OS to stop its ongoing task and attend the task for which the interrupt has been sent. These interrupts can pause service in any program of an OS. Similarly, C++ also offers various signals which it can catch and process in a program. Here is a list of various signals and their operations that C++ provides the user to work with.

Signals

Operations

SIGINT

produces a receipt for an active signal

SIGTERM

Sends a termination request to the program

SIGBUS

Bus error which indicates access to an invalid address

SIGILL

Detects an illegal command

SIGALRM

This is used by the alarm() function and indicates the expiration of the timer.

SIGABRT

Termination of a program, abnormally

SIGSTOP

The signal cannot be blocked, handled, and ignored and can stop a process

SIGSEGV

Invalid access to storage

SIGFPE

Overflow operations or mathematically incorrect operations like divide by zero

SIGUSR1

SIGSUR2



User-Defined Signals

This signal() function is provided by the signal library and is used to trap unexpected interrupts or events. 

Syntax:

signal(registered signal, signal handler)

The first argument is an integer, representing the signal number and second is the pointer to a signal handling function. We must keep in mind that the signal that we would like to catch must be registered using a signal function and it must be associated with a signal handling function. The signal handling function should be of the void type. 

Example:  

CPP




// CPP Program to demonstrate the signal() function
#include <csignal>
#include <iostream>
using namespace std;
  
void signal_handler(int signal_num)
{
    cout << "The interrupt signal is (" << signal_num
         << "). \n";
  
    // It terminates the  program
    exit(signal_num);
}
  
int main()
{
    // register signal SIGABRT and signal handler
    signal(SIGABRT, signal_handler);
  
    while (true)
        cout << "Hello GeeksforGeeks..." << endl;
    return 0;
}

Output: Being in an infinite loop this code will show the following output until an interrupt is faced:  

Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...

Now if we press Ctrl+C to send an interrupt, the program will exit by printing:  

Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
The interrupt signal is (22).

raise() function

The raise() function is used to generate signals. 

Syntax:

raise( signal )

It takes an argument as any of the functions mentioned in the list. 

Example: 

CPP




// CPP Program to demonstrate the raise() function
#include <csignal>
#include <iostream>
  
using namespace std;
  
void signal_handler(int signal_num)
{
    cout << "Interrupt signal is (" << signal_num << ").\n";
  
    // It terminates program
    exit(signal_num);
}
  
int main()
{
    int count = 0;
    signal(SIGSEGV, signal_handler);
    // register signal SIGSEGV and signal handler
  
    while (++count) {
        cout << "Hello GeeksforGeeks..." << endl;
        if (count == 5)
            raise(SIGSEGV);
    }
    return 0;
}
Output
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Hello GeeksforGeeks...
Interrupt signal is (11).

This article is contributed by Chinmoy Lenka. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 


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