Question

I writing OOP software with C++ that i need pass instances of my classes between files, 50…60 files. Unfortunately , I used a library that uses a callback function and not an object.

Question:
I used a few sates such as struct between cpp files, but i got multiple definition error or … How do I pass ONE instance from each class between 50…60 classes?

Class A{}; A *instanceA = new A();
Class B{}; B *instanceB = new B();
.
.
.
Class Z{}; Z *instanceZ = new Z();

I need to pass intaanceA, intanceB and so on between files. Do you have any idea?

Answer 1

I suspect you defined the instance in a header file and included that in multiple files:

A.h:

class A{};

A* instanceA = new A();

b.cpp and c.cpp both #include <A.h>, causing multiple definition error.

To correct you can use extern to declare the instance in the header file and define it in exactly one .cpp file:

A.h:

class A{};
extern A* instanceA;

A.cpp:

A* instanceA = new A();

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Another cause is using extern in the header file but defining instanceA in multiple .cpp files (as was the case here).