What is meant by the term “hook” in programming?

Question

I recently heard the term \"hook\" while talking to some people about a program I was writing. I\'m unsure exactly what this term implies although I inferred from the conve

Answer 1

Hooks are a category of function that allows base code to call extension code. This can be useful in situations in which a core developer wants to offer extensibility without exposing their code.

One usage of hooks is in video game mod development. A game may not allow mod developers to extend base functionality, but hooks can be added by core mod library developers. With these hooks, independent developers can have their custom code called upon any desired event, such as game loading, inventory updates, entity interactions, etc.

A common method of implementation is to give a function an empty list of callbacks, then expose the ability to extend the list of callbacks. The base code will always call the function at the same and proper time but, with an empty callback list, the function does nothing. This is by design.

A third party, then, has the opportunity to write additional code and add their new callback to the hook's callback list. With nothing more than a reference of available hooks, they have extended functionality at minimal risk to the base system.

Hooks don't allow developers to do anything that can't be done with other structures and interfaces. They are a choice to be made with consideration to the task and users (third-party developers).

For clarification: a hook allows the extension and may be implemented using callbacks. Callbacks are generally nothing more than a function pointer; the computed address of a function. There appears to be confusion in other answers/comments.