c++ - Strange behavior of static global variable -

i know program not using static variable in appropriate way, shows how reproduce behavior have seen :

main.cpp :

int main(){     myobject* p = new myobject();     header::i = 5;      printf("i %i\n", header::i);     p->update();      return 0; } 

myobject.cpp :

myobject::myobject(){ }  void myobject::update(){     printf("i %i\n", header::i); } 

extern.h :

namespace header {     static int i; }; 

the output :

i : 5 : 0 

why don't 5 both outputs ? 0come ? explain how static variables work ?

static variables have internal linkage means local compilation unit. since have static variable declared in header included in 2 source files, have 2 distinct variables: 1 i local myobject.cpp , another, different i, local main.cpp