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

The best solution is to separate interface and implementation. Interface is your h-file. Put only prototypes there. Implementation goes to cpp-file. This approach has the following advantages:

1. Compilation goes faster because there is no need to compile function bodies several times.
2. Header dependency is simpler because there is no need to include all headers to h-file. Some of the headers are needed only in cpp-file and you can use forward declarations in h-file. Also you can avoid circular dependencies.
3. The last but not the least – it is easier for human beings to understand interface of your class. There is no code mess.