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I have been looking around but I have not found any question that really helps me to solve this issue. I am not very experienced, so maybe this problem is trivial and it is a question of my lack of knowledge.

I am trying to solve an issue. Our system has a Logger that takes different logs and puts them into a SharedMemory.

However, from one of our classes (a StateMachine) I can not use the Loogger because of recursion:

  • Logger.h includes SharedMemory.h

  • SharedMemory.h includes StateMachine.h

If I include Logger.h in StateMachine.h, compile errors appear everywhere. First i was trying to fix this problem by creating a second SharedMemory that is dedicated exclusively to the Logger and don't include StateMachine.h.

With this approach, the compilation errors were solved, but my manager does not like this design solution.

I have also tried to change include order, and to declare class before the include but it is not working (e.g. declare class SharedMachine; before #include SharedMachine.h)

The includes are like this:

In the StateMachine.h

#ifndef SM_H

#define SM_H

#include <map> 

/* (different includes) */

#include Logger.h

In the Logger.h

#include SharedMemory.h

In the SharedMemory.h

#include StateMachine.h

I would like to know if there is any trick that I can use to make the includes work in this way, without architectural changes (that my manager seems not to like).

anatolyg
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Alejandro Martinez
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    Use forward declarations instead including the entire file [(what is forward declarations)](https://stackoverflow.com/questions/4757565/what-are-forward-declarations-in-c) – Equod Jul 30 '20 at 10:35
  • The terms you want to be searching for are "forward declaration" and "circular dependency" – JMAA Jul 30 '20 at 10:36
  • The core of the problem is within those headers. Why do you think that you need to include them? Something that depends on logger cannot possible be depended on by logger. You cannot have cycles in dependency trees. – eerorika Jul 30 '20 at 10:38
  • ´Thank you very much for your answers, I have tried to create a forwards declaration in State_Machine, writing the definition of the Logger there, but then bring me to a redefinition error. Also header guards are in all my header files so I think is not the issue. I am reading questions now about "circular dependency", maybe there will be something – Alejandro Martinez Jul 30 '20 at 10:55

1 Answers1

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  1. Try to move includes from header files to source (*.cpp) files
  2. Use forward declarations: What are forward declarations in C++?
  3. Change interfaces to work with pointers or references to needed types instead of using actual types, to make possible using forward declaration (if needed)
Ihor Drachuk
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  • Thank you very much, it seems that as you told, if I place the include in the *.cpp file everything works fine! i have just move the #include Logger/logger.h to the State_Machine.cpp and it is working – Alejandro Martinez Jul 30 '20 at 11:08