C++ performance of accessing member variables versus local variables

Question

Is it more efficient for a class to access member variables or local variables? For example, suppose you have a (callback) method whose sole responsibility is to receive dat

Answer 1

Using the member variables should be marginally faster since they only have to be allocated once (when the object is constructed) instead of every time the callback is invoked. But in comparison to the rest of the work you're probably doing I expect this would be a very tiny percentage. Benckmark both and see which is faster.