Question

I am having some trouble understanding the following simple C code:

int main(int argc, char *argv[]) {
    int n=0;
    fork();
    n++;
    printf("hello: %d\n", n);
}

My current understanding of a fork is that from that line of code on, it will split the rest of the code in 2, that will run in parallel until there is “no more code” to execute.

From that prism, the code after the fork would be:

a)

    n++;                       //sets n = 1
    printf("hello: %d\n", n);  //prints "hello: 1"

b)

    n++;                       //sets n = 2
    printf("hello: %d\n", n);  //prints "hello: 2"

What happens, though, is that both print

hello: 1

Why is that?

EDIT: Only now it ocurred to me that contrary to threads, processes don’t share the same memory. Is that right? If yes, then that’d be the reason.

Answer 1

fork() starts a new process, sharing no variables/memory locations.
It is very similar to what happens if you execute ./yourprogram twice in a shell, assuming the first thing the program does is forking.