Is it a good practice to have half implementation into headers and half to .cpp file?

[babaliaris]

Hello!

I'm trying to make a library in C++ in such a way that code which I don't want the client to recompile, be inside a .dll and the rest of it is implemented into the header files so that the user can Include them
and compile them by himself. To achieve that while I'm writing the library implementation into the header files, I'm also creating a .cpp file for each header that needs to hide some of the implementation into the dll.
The the implementation inside the header file is calling extern c functions to run the hidden implementation.

The problem is, that after a week which I did a lot of work, now I'm getting errors use of undefined type while compiling some cpp files. I know what causes this errors but its unbelievable difficult to figure how to solve it. Let me tell you an example.

I have Core.cpp which inludes:
Core.h->Scene.h->Sprite.h->Animation.h->Core.h (I'm using header guards so there is no circular inclusion)

Now, Core.cpp is trying to compile Animation.h which uses Core instances. But because inside Core.h, Animation.h is included before the definitions of Core.h this is why I'm getting the error:
Animation.h use of undefined type Core

The thing is that I tried to define the header guard of Animation.h inside the Core.cpp, because there is no point of compiling Animation.h inside this cpp file but this causes other problems when compiling Animation.cpp .

I know that YOU SHOULD not actually have implementations on header files while using cpp files so I'm asking you if it's better to drop that thinking of making this library and find another way.

Generally, there is a mess with the inclusions in my project. Everything is including stuff "from here and there". When i was making cpp aplications and I was following the method of keeping implementations inside cpps and in header files only declarations, i never had problems like that.

[2kaud]

Do you mean that for example say core.h uses a class defined in animation.h and that animation.h uses a class defined in core.h?

if so, then this is a no-no as you have a circular class reference dependency. You either need to break this dependency by introducing another class or to use a pointer in the first class definition to the other class and have a class forward reference in the first definition. Except when used as a pointer, a class can't be used until it is fully defined. Have a look at post #4 of http://forums.codeguru.com/showthrea...ke-1-arguments

If this isn't the case, then can you provide some more info please.

[babaliaris]

Do you mean that for example say core.h uses a class defined in animation.h and that animation.h uses a class defined in core.h?

if so, then this is a no-no as you have a circular class reference dependency. You either need to break this dependency by introducing another class or to use a pointer in the first class definition to the other class and have a class forward reference in the first definition. Except when used as a pointer, a class can't be used until it is fully defined. Have a look at post #4 of http://forums.codeguru.com/showthrea...ke-1-arguments

If this isn't the case, then can you provide some more info please.

Yea that's it. I know about Pointer To Implementation but when I was doing that I didn't thought that I will need it at that point.
I have increased the difficulty of my project for no reason actually.

To avoid this problem I used to follow these rules:
1) Create declarations inside header files.
2) Implement them inside .cpp files.
3) Never include headers inside headers (Except standard c++ headers). Manually forward declare inside header files only classes or functions which you are interesting in and use pointer references. Then allocate and use them in the .cpp file. Now if it is very important to stack allocate them, then and only then include the header file and make sure no problems will occur.