CODEWITHSUNDEEP
c++cprocessexec
Ahmed A
Ahmed A

Reputation: 3652

execl not running programming

I have the following two simple programs:

bye.cc

#include <iostream>

int main()
{ std::cout <<  "Bye bye bye world" << std::endl; }

hello.cc

#include <cstdlib>
#include <unistd.h>
#include <sys/wait.h>
#include <iostream>
using namespace std;


int main()
{
    int status;

    cout <<  "Hello world" << endl;

    int pid = fork();
    if (pid != 0) {
        cout << "I am parent - " << pid << endl;
        // wait for child to finish up......
        cout << "Waiting for child to finish" << endl;
        wait(&status);
        cout << "Child finished, status " << status << endl;
    } else {
        cout << "--- I am child - " << pid << endl;   // **Note**
        execl("bye", "");
        cout << "--- I am sleeping" << endl;
        sleep(3);
        exit(11);
    }
}

In hello.cc, if the line marked "Note" is enabled (not commented), I get the expected behavior, sleep(3) is not executed, and "bye" is executed, expected msg printed to console.

$ ./hello
Hello world
I am parent - 27318
Waiting for child to finish
--- I am child - 0
Bye bye bye world
Child finished, status 0

However, when the line marked "Note" is commented, "bye" is NOT executed, and sleep(3) is performed.

$ ./hello
Hello world
I am parent - 27350
Waiting for child to finish
--- I am sleeping
Child finished, status 2816

Can someone please help me understand what might be going on. What I found very odd, if I replace the "cout" with a printf(), then the sleep performed.

Thank you, Ahmed.

Upvotes: 1

Views: 353

Answers (2)

user3629249
user3629249

Reputation: 16540

the exec family of functions, when successful, do not return. That is why you do not see the sleep comment when the execl() is executed.

Upvotes: 0

Nemo
Nemo

Reputation: 71525

According to the spec, the argument list to execl must be terminated by a NULL pointer (i.e. (char *)0, not "").

Changing the nearby code is just changing what happens to be on the stack when you invoke execl. As written, the program's behavior is undefined.

P.S. Always check the return value of library routines for errors.

Upvotes: 1

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