Question

Consider this pointless program:

/* main.c */

#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv) {
    int i;
    for (i = 0; i < 1024; i++) {
        int pid = fork();
        int status;
        if (pid) {
            wait(&status);
        }
        else {
            char *ptr = (char *)malloc(1024*sizeof(char));
            char *args[2] = {"Hello, world!", NULL};
            execve("/bin/echo", args, NULL);
        }
    }
}

Would not freeing ptr constitute a memory leak for either main.c or the other program, or is it going to be freed anyway when execve is called?

Answer 1

No.

This is not a memory leak. exec*() will make a local copy of the string data in the args array, then blow away the child process memory image and overlay it with the memory image used by /bin/echo. Essentially all that remains after the exec() is the pid.

Edit:

User318904 brought up the case of exec() returning -1 (i.e., failure). In this case, the child process that has forked but failed to exec does, indeed technically have a memory leak, but as the usual response to a failed exec is to just exit the child process anyways, the memory will be reclaimed by the OS. Still, freeing it is probably a good habit to get into, if for no other reason than that it will keep you from wondering about it later on.