❮ C Exercise Example6 C Examples Factors Number ❯

C Library Function - `signal()`

C Standard Library - <signal.h>

Description

The C library function void (signal(int sig, void (func)(int)))(int) sets a function to handle a signal, i.e., a signal handler with the sig parameter.

Declaration

Here is the declaration for the signal() function.

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

Parameters

sig -- The signal code used as a variable in the signal handler. Below are some important standard signal constants:

Macro	Signal
SIGABRT	(Signal Abort) Abnormal termination of the program.
SIGFPE	(Signal Floating-Point Exception) Arithmetic operation error, such as division by zero or overflow (not necessarily floating-point operations).
SIGILL	(Signal Illegal Instruction) Illegal function image, such as an illegal instruction, usually due to a variant in the code or an attempt to execute data.
SIGINT	(Signal Interrupt) Interrupt signal, such as ctrl-C, usually generated by the user.
SIGSEGV	(Signal Segmentation Violation) Illegal memory access, such as accessing a non-existent memory unit.
SIGTERM	(Signal Terminate) Termination request signal sent to the program.

func -- A pointer to a function. It can be a function defined by the program or one of the following predefined functions:

Return Value

The function returns the previous value of the signal handler, or SIG_ERR on error.

Example

The following example demonstrates the use of the signal() function.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>

void sighandler(int);

int main()
{
   signal(SIGINT, sighandler);

   while(1) 
   {
      printf("Sleeping for one second...\n");
      sleep(1);
   }

   return(0);
}

void sighandler(int signum)
{
   printf("Caught signal %d, exiting...\n", signum);
   exit(1);
}

Let's compile and run the above program, which will produce the following result and enter an infinite loop, requiring the use of CTRL + C to exit the program.

Sleeping for one second...
Sleeping for one second...
Sleeping for one second...
Sleeping for one second...
Sleeping for one second...
Caught signal 2, exiting...