Question

I have 4 classes:
Server.cpp Logger.cpp Util.cpp Crypto.cpp

The class Server use the object Util.
The program works fine, but now I need to use the object Util also in the class Logger.
But when I put in the code #include “Util.cpp” g++ give me an error because I cannot call again the object.
Eclipse told me about the “redefinition” and “previous declaration” of class Util.

How can I solve this?

Answer 1

You should not include the source cpp files in to another cpp file.
This basically violates the One Definition Rule resulting in redefinition errors.

Include the header file which has the definiition of Util class in whichever class you want to create its objects.

Basically, Your code should be organized in this fashion(exception: Templatized code):

Util.h ———–> Contains Definition of class Util acts as Interface
Util.cpp ———–> Contains Implementation of class Util acts as Implementation

Here on whenever you want to create an object of class Util in any of the cpp files you include Util.h in that cpp file so the compiler knows the definition of class Util.

For ex:
Server.cpp wants to create an object of Util then your Server.cpp should include Util.h as:

#include "Util.h"

Also, don’t forget to add Include guards to your header files.

If the usage of Util by another source/header file is limited to creating a pointer to Util then you do not need to include the header file, You only need to Forward declare the Util class.