Memory allocated with alloca gets freed at end of function or at end of scope?

Question

If I have a function like this:

void bla(int size) {
    while(b){
        char tmp[size];
        ......
    }
}

tmp gets freed at each iteration of the while loop, right?

If I write this function:

void bla(int size) {
    while(b){
        char* tmp = alloca(size);
        ......
    }
}

tmp gets freed at end of scope or at end of function?

Answer 1

It will be freed at end of function, but since you call alloca() inside the loop you'll likely get stack overflow. If size doesn't change within the function you should call alloca() before the loop.