Linked list head double pointer passing

Question

I have seen this in some book/ tutorial.

When you pass in the head pointer (of linked list) into a function, you need to pass it as a double pointer.

For eg:

Answer 1

That last head=prev; does not change the passed pointer's value in the second example. Whether or not that line is necessary for the purposes of this function is up to you. But there is a difference.

How did you test that it "worked fine"? Were you able to iterate the list and print out the node's values and see that they had in fact been reversed? The first function (presumably called like nReverse(&list); changes what list points to, the second do not (so for the second how do you know which node is the beginning of the list, after all it was just changed...).