Question

Does Boost, or anything else, contain a container will act like a shared pointer but allow me to control what happens to the shared ‘resource’ at the end of it’s life? I want to encapsulate an object that can be handed around but, when no longer needed can be closed in a context defined way.

For example, I might want to create and pass around a file handle knowing that when it goes out of scope, the file will be closed automatically, but I don’t want to delete the handle.

I could implement it myself, but would rather not get into that if the framework already exists – someone has no doubt done it better. I can’t use boost::shared_ptr, at least not in it’s normal form, as the resource should not be deleted at end of life.

Answer 1

Are you aware that std::shared_ptr can take a custom deleter class? This need not actually use “delete” or “free”, but could easily use some other sort of mechanism (such as a reference counting mechanism’s release and so on).

Here’s a dead simple example for you:

std::shared_ptr<FILE> foo(fopen("la", "r"), fclose);

The deleter just needs to be a function that takes the pointer type that the shared_ptr wraps. In this case, whenfoo goes out of scope, shared_ptr will close the file for you. (Note: this isn’t a totally sensible implementation, because no error values are checked. It is just an example).