C library function - signal()


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Description

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

Declaration

Following is the declaration for signal() function.

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

Parameters

  • sig − This is the signal number to which a handling function is set. The following are few important standard signal numbers −

Sr.No. Macro & Signal
1

SIGABRT

(Signal Abort) Abnormal termination, such as is initiated by the function.

2

SIGFPE

(Signal Floating-Point Exception) Erroneous arithmetic operation, such as zero divide or an operation resulting in overflow (not necessarily with a floating-point operation).

3

SIGILL

(Signal Illegal Instruction) Invalid function image, such as an illegal instruction. This is generally due to a corruption in the code or to an attempt to execute data.

4

SIGINT

(Signal Interrupt) Interactive attention signal. Generally generated by the application user.

5

SIGSEGV

(Signal Segmentation Violation) Invalid access to storage − When a program tries to read or write outside the memory it is allocated for it.

6

SIGTERM

(Signal Terminate) Termination request sent to program.

  • func − This is a pointer to a function. This can be a function defined by the programmer or one of the following predefined functions −

Sr.No. Function & Description
1

SIG_DFL

Default handling − The signal is handled by the default action for that particular signal.

2

SIG_IGN

Ignore Signal − The signal is ignored.

Return Value

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

Example

The following example shows the usage of 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("Going to sleep for a second...\n");
      sleep(1); 
   }
   return(0);
}

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

Let us compile and run the above program that will produce the following result and program will go in infinite loop. To come out of the program we used CTRL + C keys.

Going to sleep for a second...
Going to sleep for a second...
Going to sleep for a second...
Going to sleep for a second...
Going to sleep for a second...
Caught signal 2, coming out...

signal_h.htm

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