关于链接器和多个类声明的 C++ 问题

Question

So I have a file called test.cpp

class Entity
{
    int c = 0;
    int b = 0;
    int d = 5;

};

And then another called main.cpp

#include<iostream>
#include<vector>
#include<algorithm>
class Entity
{

    int a = 5;
    int b = 0;


};
int main()
{
    
}

Why does this link and work just fine? Doesn't the linker see that there are 2 classes with the same name and different data members? Also would these be considered class definitions? If I wanna declare this class in a header file I would just do what I did here right? Even though I'm technically defining variables it's still just a class declaration right..?

Answer 1

It is an ill-formed program.

As the class definition has external linkage then each definition of the class shall consist of the same sequence of tokens.

On the other hand, as neither code from the translation unit test.cpp is used the linker can exclude it from the final exe file.