What is double star (eg. NSError **)?

Question

So, I saw this:

error:(NSError **)error

in the apple doc\'s. Why two stars? What is the significance?

Answer 1

In C, a double star is a pointer to a pointer. There are a couple of reasons to do this. First is that the pointer might be to an array of pointers. Another reason would be to pass a pointer to a function, where the function modifies the pointer (similar to an "out" parameter in other languages).