What is the "Pass by * &" for?

Question

What does it mean? I understand the use of pass by reference is to pass in the reference so you can directly alter it without the need of a return, and pass by pointer is similar but with a slower runtime. However, I do not understand what * & does. For an example,

foo(int * & var) { }

Answer 1

It passes a pointer by reference so that you can change what the pointer points to and have those changes reflected to the caller.

For example:

void notByReference(int *p) {
    p = nullptr;
}

void byReference(int *&p) {
    p = nullptr;
}

int main() {
    int *i = new int;
    notByReference(i); //i is not changed since a copy of the pointer was passed
    byReference(i); //i itself is changed, leaking memory
}

Answer 2

This allows you to pass a pointer by reference. Which gives the function the opportunity to modify the pointer and have that modification seen by the caller.

You don't need to stop there. You can pass by reference a pointer to pointer to int, for example.

void foo(int** &var)