What does the '&' symbol in front of a variable do?

Question

I've been going through some open-source code for a Twitter app, and came across this:

(in the OADataFetcher.h) file:

OAMutableURLRequest *request;
NSURLResponse *response;
NSError *error;
NSData *responseData;

(inside the 'fetchDataWithRequest:delegate:didFinishSelector:didFailSelector:' method) in OADataFetcher.m:

responseData = [NSURLConnection sendSynchronousRequest:request
                                         returningResponse:&response
                                                     error:&error];

I was wondering if someone can please explain to me what the '&' symbol does in front of the returningResponse and error variables. How is it different then simply using the variables without the ampersand?

Answer 1

The & is the "address-of" operator. It returns the address of (pointer to) the variable it precedes.