exec function. Is there a way to back to the main program?

Question

I've a problem with exec() function under ubuntu. Is there any possibility to go back to the main program?

example:

printf("Some instructions at beginning\n");
execlp("ls","ls", "-l", NULL);

// i want to continue this program after exec and see the text below
printf("Other instructions\n");

Answer 1

No. A successful exec call replaces the current program with another program. If you want both the parent and child to stick around, you need to call fork(2) before exec:

pid_t childpid = fork();
if(childpid < 0)
{
    // Handle error
}
else if(childpid == 0)
{
    // We are the child
    exec(...);
}
else
{
    // We are the parent: interact with the child, wait for it, etc.
}

Note that a failed exec call (e.g. the given executable doesn't exist) does return. If exec returns, it's always because of an error, so be prepared to handle the error.

Answer 2

exec replaces the executable file image. There is no way back. A nice alternative is vfork() exec. vfork copies the process, continues in the copy and when it completes its execution, continues the main process. The copy can exec the desired file. Example:

printf("Some instructions at beginning\n");
if(!vfork()){
    // child
    execlp("ls","ls", "-l", NULL); // child is replaced
}
// parent continues after child is gone
printf("Other instructions\n");

Answer 3

No, Not possible using exec family functions because the executable file, which is generated from your previous code i.e. code which contains execlp("ls","ls","-l",NULL) function, is replaced by the executable file you are going to run by execlp() function i.e. ls. So when this function is executed successfully, you no more have that old executable file containing execlp() function.

Use system("ls -l"); function if you want to run any other process and want to return to current process.