How can a C++ header file include implementation?

Question

Ok, not a C/C++ expert by any means, but I thought the point of a header file was to declare the functions, then the C/CPP file was to define the implementation.

How

Answer 1

Keeping the implementation in the class header file works, as I'm sure you know if you compiled your code. The const keyword ensures you don't change any members, it keeps the instance immutable for the duration of the method call.