C: What is call back function and when it is used ?

Question

Which is the best practice for variable declaration within the function ? Or is it vary from one language to other one ?

Answer 1

This is a very common c programming question asked in interview. When a function (callee) is called through another function (caller) using the function pointer, known as call back. Kernel generates different kinds of signals and user space process may register its own signal handler using call back mechanism. Sample of c code is as below:

struct sigaction act;

/* signal handler definition goes here */
void sig_handler(int signo, siginfo_t *si, void *ucontext)
{
printf("Got alarm signal %d\n",signo);
/* do the required stuff here */
}

int main(void)
{
act.sa_sigaction = sig_handler;
act.sa_flags = SA_SIGINFO;

/* register signal handler */
sigaction(SIGALRM, &act, NULL);  
/* set the alarm for 10 sec */       
alarm(10);   
/* wait for any signal from kernel */                                        
pause();  
/* after signal handler execution */                                             
printf("back to main\n");                     
return 0;

}