static initialization confusion

Question

I am getting very confused in some concepts in c++. For ex: I have following two files

//file1.cpp
class test
{
    static int s;
    public:
    test(){s++;}
};

static test t;
int test::s=5;

//file2.cpp
#include<iostream>
using namespace std;
class test
{
    static int s;
    public:
    test(){s++;}
    static int get()
    {
    return s;
    }
};

static test t;

int main()
{
    cout<<test::get()<<endl;
}

Now My question is :
1. How two files link successfully even if they have different class definitions?
2. Are the static member s of two classes related because I get output as 7.

Please explain this concept of statics.

Answer 1

They link because the linker knows almost nothing about the C++ language. However, if you do this, you have broken the One Definition Rule, and the behaviour of your program will be undefined. writing invalid code is not a good way of learning C++. Also, you seem to be having a lot of questions about static variables - the concept is really not all that complex - which C++ textbook are you using that does not explain it well?

Answer 2

The classes are (as far as the linker is concerned) identical. get() is just an inline function the linker never sees.

static in a class doesn't limit the member to file scope, but makes it global for all class instances.

[edit:] You'd get an linker error if you would put int test::s=5; into the second file as well.