Function hooking in C++?

Question

With \"hooking\" I mean the ability to non-intrusively override the behavior of a function. Some examples:

• Print a log message before and/or after the function

Answer 1

1. There has to be a way to implement the functionality without affecting the performance of code that doesn't use the functionality. C++ is designed on the principle that you only pay performance costs for the features you use. Inserting if checks in every function to check if its been overridden would be unacceptably slow for many C++ projects. In particular, making it work so that there's no performance cost while still allowing for independent compilation of the overridden and overriding functions will be tricky. If you only allow for compile time overriding, then it's easier to do performantly (the linker can take care of overwriting addresses), but you're comparing to ruby and javascript which let you change these things at runtime.

2. Because it would subvert the type system. What does it mean for a function to be private or non-virtual if someone can override its behavior anyway?

3. Readability would greatly suffer. Any function might have its behavior overridden somewhere else in the code! The more context you need to understand what a function does, the harder it is to figure out a large code base. Hooking is a bug, not a feature. At least if being able to read what you wrote months later is a requirement.