Extern Struct in C++?

You put the struct MyStruct type declaration in a .h file and include it in both class1.cpp and class2.cpp.

IOW:

Myst.h

struct MyStruct {
 int x;
};

Class1.cpp

#include "Myst.h"

MyStruct theVar;

Class2.cpp

#include "Myst.h"

extern struct MyStruct theVar;

void test() {
 int t = theVar.x;
}