C library - raise() function

The C library raise(sig) function causes signal sig to be generated. The sig argument is compatible with the SIG macros.

Two types of Signal Handling −

Testing Signal Handling: In this signal handling, we use raise() to check whether a signal handler responds correctly to a specific signal.
Custom Signal Handling: If user want to set the custom signal handling using signal() function then we can use raise() function to call the handler explicitly.

Syntax

Following is the syntax of the C library raise() function −

int raise(int sig)

Parameters

This function accepts only a singal parameter −

sig − This is the signal number to send. Following are few important standard signal constants −

Sr.No.	Macro & Signal
1	SIGABRT (Signal Abort) The Abnormal termination which is initiated by the abort 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.

Return Value

This function returns zero if it is successful otherwise non-zero.

Example 1

In this example, we use the C library raise() function to see its demonstration.

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

void signal_catchfunc(int);

int main () {
   int ret;

   ret = signal(SIGINT, signal_catchfunc);

   if( ret == SIG_ERR) {
      printf("Error: unable to set signal handler.\n");
      exit(0);
   }
   printf("Going to raise a signal\n");
   ret = raise(SIGINT);
   
   if( ret !=0 ) {
      printf("Error: unable to raise SIGINT signal.\n");
      exit(0);
   }

   printf("Exiting...\n");
   return(0);
}

void signal_catchfunc(int signal) {
   printf("!! signal caught !!\n");
}

Output

The above code produces the following result −

Going to raise a signal
!! signal caught !!
Exiting...

Example 2

In this example, we illustrate the signal reciever and sender using the functions − signal() and raise().

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

void handler(int sig) {
   // Signal receiver
   printf("Signal received : %d\n", sig);
}

int main() {
   signal(SIGILL, handler);
   // Signal sender
   printf("Signal Sended : %d\n", SIGILL);
   raise(SIGILL);
   return 0;
}

Output

On execution of above code, we get the following result −

Signal Sended : 4
Signal received : 4

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