What is the practical use of pointers to member functions?

Question

I\'ve read through this article, and what I take from it is that when you want to call a pointer to a member function, you need an instance (either a pointer to one or a sta

Answer 1

Member functions, like many function pointers, act as callbacks. You could manage without them by creating some abstract class that calls your method, but this can be a lot of extra work.

One common use is algorithms. In std::for_each, we may want to call a member function of the class of each member of our collection. We also may want to call the member function of our own class on each member of the collection - the latter requires boost::bind to achieve, the former can be done with the STL mem_fun family of classes (if we don't have a collection of shared_ptr, in which case we need to boost::bind in this case too). We could also use a member function as a predicate in certain lookup or sort algorithms. (This removes our need to write a custom class that overloads operator() to call a member of our class, we just pass it in directly to boost::bind).

The other use, as I mentioned, are callbacks, often in event-driven code. When an operation has completed we want a method of our class called to handle the completion. This can often be wrapped into a boost::bind functor. In this case we have to be very careful to manage the lifetime of these objects correctly and their thread-safety (especially as it can be very hard to debug if something goes wrong). Still, it once again can save us from writing large amounts of "wrapper" code.