q about globals inititialization order and solutions

[sergey akifiev]

another one simple q:
i have one program:

Code: Select all

//: C10:Out.cpp {O}
// First file
#include <fstream>
std::ofstream out("out.txt"); ///:~
//: C10:Oof.cpp
// Second file
//{L} Out
#include <fstream>
extern std::ofstream out;
class Oof {
public:
  Oof() { std::out << "ouch"; }
} oof;
int main() {} ///:~

it segfaults, as supposed, with "correct" :-) linking order
and another program:

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Mirror.h :
#ifndef MIRROR_H
#define MIRROR_H
class Mirror {
  bool b;
  Mirror* ptr;
 public:
  Mirror() {
    b = true;
    ptr = 0;
  }
  Mirror(Mirror* p) {
    b = false;
    ptr = p;
  }
  bool test() {
    if(ptr)
      return ptr->test();
    else
      return b;
  }
};
#endif // MIRROR_H

Mirror1.cpp :
#include "Mirror.h"
Mirror globalMirror;

Mirror2.cpp :
#include "Mirror.h"
extern Mirror globalMirror;
Mirror secondGlobalMirror(&globalMirror);
 ... and so on, totally of 5 files
MirrorMain.cpp : 
#include <iostream>
#include "Mirror.h"
using namespace std;
extern Mirror fifthGlobalMirror;
int main() {
  if(fifthGlobalMirror.test())
    cout << "true" << endl;
  else
    cout << "false" << endl;
}

but it doesn't work incorrectly (print false, instead of true), "ignoring" linking order.
or, may be, i wrote it wrong?
task was (taken from "Thinkig in C++" by Bruce Eckel):
31 In a header file, create a class Mirror that contains two data members: a pointer to a Mirror object and a bool. Give it two constructors: the default constructor initializes the bool to true and the Mirror pointer to zero. The second constructor takes as an argument a pointer to a Mirror object, which it assigns to the object’s internal pointer; it sets the bool to false. Add a member function test( ): if the object’s pointer is nonzero, it returns the value of test( ) called through the pointer. If the pointer is zero, it returns the bool. Now create five cpp files, each of which includes the Mirror header. The first cpp file defines a global Mirror object using the default constructor. The second file declares the object in the first file as extern, and defines a global Mirror object using the second constructor, with a pointer to the first object. Keep doing this until you reach the last file, which will also contain a global object definition. In that file, main( ) should call the test( ) function and report the result. If the result is true, find out how to change the linking order for your linker and change it until the result is false.

[sergey akifiev]

and also, i don't know, how to implement next task:
33 Repair the problem in Exercise 32 using technique one shown in this book.
34 Repair the problem in Exercise 32 using technique two shown in this book.

theese techniques are: use of special initializer class and using of "wrapper" functions.
[edit]
for 33 i wrote something like that:

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#ifndef INITIALIZER_H
#define INITIALIZER_H
#include "Mirror.h"

extern Mirror globalMirror;
extern Mirror secondGlobalMirror;
extern Mirror thirdGlobalMirror;
extern Mirror forthGlobalMirror;
extern Mirror fifthGlobalMirror;

class Initializer {
  static int initCount;
  public:
  Initializer() {
    std::cout << "Initializer()" << std::endl;
    if(initCount++ == 0) {
      std::cout << "  performing initialization" << endl;

      // some init here. what should i put here?
    }
  }
}

static Initializer init;
#endif // INITIALIZER_H

but i don't know what to put for initialization of my globals?