Question

file1.cpp

#include <iostream>

extern int u;
int i=9;
int j=i+9;
int main()
{
   std::cout<<u;
   return 0;
}

file2.cpp

extern int j;
int u=j+9;

Result is u=9 but not 27

This shows that j is initialized twice – First zero(due to which variable u get value 9) and then with 18

Is it possible ?? My meaning for initialization is destroyed here.

I also try to make variable j constant to see what will happen next

file1.cpp //after changing j to constant

extern int u;
int i=9;
extern const int j=i+9;

This has same output as before.

However if I change int j=i+9;(in file1.cpp) to int j=9;

Surprisingly, I got correct values i.e. u=18;

Answer 1

The order of initialization of global variables declares across different translation Units is not specified.

The globals u and i, j reside in different translation units in your code, so the order whether u gets initialized first or i & j get initialized before u is Unspecified.
This invokes an Undefined Behavior in your code.
This invokes an Unspecified Behavior in your code

However, Note that order of initialization of globals in the same translation unit is well-defined.
i.e: it is well defined that i will be initialized before j in your code.

What you are seeing is a classic case of Static Initialization Fiasco.