fork() and exec()

[Vijay Chauhan]

Thank you all for your help.

Vijay.

On Tue, Feb 7, 2012 at 9:10 PM, Bernd Petrovitsch
<bernd at petrovitsch.priv.at> wrote:
> 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
>