Can I get examples for static keyword in header file?

static.h

static int y = 20;
static int& f(){
    static int x = 0;
    return x;
}

general.h

int x = 10;
int& g(){
    static int x = 0;
    return x;
}

outer.h

#include"general.h"
#include"static.h"

void h(){
    x = 20;//static
    y = 20;//non static

    f() = 20;//static
    g() = 20;//non static
}

main.cpp

#include<iostream>
#include"static.h"
#include"general.h"
#include"outer.h"

int main(){
    h();
    std::cout<<"static objects are independent in each file\n";
    std::cout<<"x : "<<x<<", f() : "<<f()<<std::endl;
    std::cout<<"non static objects are only one in every file.\n ";
    std::cout<<"y : "<<y<<", g() : "<<g()<<std::endl;
}

I want to simulate how static keyword changes code behavior.
but, I don't know how to do that...
How do I do?

.....................................................
I split my code.
static.h

static int x = 0;
static int& f(){
    static int k = 0;
    return k;
}
void call_static();

static.cpp

#include"static.h"

void call_static(){
    x = 10;
    f() = 10;
}

general.h

int y = 0;
int& g(){
    static int z = 0;
    return z;
}
void call_general();

general.cpp

#include"general.h"
void call_general(){
    y = 10;
    g() = 10;
}

Static codes are compiled well, but non static codes aren't compiled.

error code

/usr/bin/ld: /tmp/general-539e11.o: in function `g()':
general.cpp:(.text+0x0): multiple definition of `g()'; /tmp/main-5f12cd.o:main.cpp:(.text+0x0): first defined here
/usr/bin/ld: /tmp/general-539e11.o:(.bss+0x0): multiple definition of `y'; /tmp/main-5f12cd.o:(.bss+0x4): first defined here
clang-12: error: linker command failed with exit code 1 (use -v to see invocation)

Is it normal?