Question

I’m using extern to fetch variables from another class, and it works fine for int’s, float’s etc…

But this doesn’t work, and I don’t know how to do it:

Class1.cpp

struct MyStruct {
 int x;
}

MyStruct theVar;

Class2.cpp

extern MyStruct theVar;

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

It doesn’t work because Class2 doesn’t know what MyStruct is.

How do I fix this?

I tried declaring the same struct in Class2.cpp, and it compiled, but the values were wrong.

Answer 1

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;
}