Class member function declaration doubt

Question

I'm reading a C++ tutorial and I've ran into this sentence:

The only difference between defining a class member function completely within its class or to include only the prototype and later its definition, is that in the first case the function will automatically be considered an inline member function by the compiler, while in the second it will be a normal (not-inline) class member function, which in fact supposes no difference in behavior.

I know what an inline function is, my doubt is about which style to choose. Should I define every function inside its class or outside? Perhaps the simplest functions inside and the other outside?
I fear that defining every function inside a class (i.e. having complex inline functions) might mess up the resulting code and introduce debugging problems or weird behaviors during execution. And, finally, there's the "coding style" issue. So,
which approach is better?

Thank you :)

Answer 1

My style: I sometimes will put extremely short (one or two liner) functions in the class itself. Anything longer that I still want as an inlined function go as inline qualified implementations after the class definition, and oftentimes in a separate file that the header #includes at the end of the class definition.

The rationale for putting an inlined function outside the class is that the implementation of some function usually just gets in the way of a human reader's overall understanding of the class. A twenty line function can usually be summarized in a one line comment -- and that comment is all that is needed when you are reading the class definition. If you need more, go to the function definition, or better yet, Read The Fine Documentation. (Expecting someone to Read The F*** Code is a poor substitute for Fine Documentation.)