On Die, 2012-02-07 at 00:38 +0530, Vijay Chauhan wrote:

Hi List,

I am learning Linux and trying to understand exec and fork function.
execl says that it overlays the running address space. What does it mean?

I created the following program and used top command with
intentionally wrong arguments:

#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<stdlib.h>

int main(){
	int a = -1;
	if(fork()==0){
		printf("Inside child\n");
		printf("child pid=%d, parentid=%d\n", getpid(), getppid());
		execl("/usr/bin/top", "/usr/bin/top", ">/dev/null" ,(char*)0 );

You get here only if the execl() as such fails.

		scanf("inside child provide a %d", &a);

You should check the return value here if you actually got a matching
parameter.
scanf() is actually a function to be avoided.

		printf("Inside child a=%d\n", a);
		exit(1);
	} else {
		printf("Inside parent, going to wait\n");
		printf("my pid=%d, parentid=%d\n", getpid(), getppid());
		scanf("input parent %d\n", &a);

You should check the return value here if you actually got a matching
parameter.
scanf() is actually a function to be avoided.

		wait(NULL);

You should check the return value here to know why "wait()" returns.

		printf("Wait over\n");
		printf("Inside parent a=%d\n", a);
	}
	return 0;
}

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd at petrovitsch.priv.at
                     LUGA : http://www.luga.at