Thread: Problem with global variables

Bare with me :/

I have two class definitions in file MyClass.h:

Code:

#define MYCLASS_H

class MyClass
{
    int i;

    public:
        MyClass(int n):i(n){}
        int GetI(void){return i;}
};

class MyClass2
{
    float x;

    public:
        MyClass2(float n):x(n){}
        float GetX(void){return x;}
        void DoStuffToX(void);
};

I then have a file named globals.h with a global object of type MyClass in a namespace:

Code:

#define GLOBALS_H

#ifndef MYCLASS_H
    #include "myClass.h"
#endif

namespace my_name
{
    MyClass myObject(234);
}

I then have a file called MyMain.cpp which includes both header files and refers to my global MyClass object:

Code:

#include <iostream>

#ifndef GLOBALS_H
    #include "globals.h"
#endif

#ifndef MYCLASS_H
    #include "myClass.h"
#endif



int main()
{
    cout << my_name::myObject.GetI();
    cin.get();

  return 0;
}

Now, at this point in the operation everything compiles and works fine; we have an output on the screen of "234". Hoorah. The error occurrs when I try adding another file wanting to include globals.h. This one is called MyClass2.cpp:

Code:

#ifndef MYCLASS_H
    #include "myClass.h"
#endif
#ifndef GLOBALS_H
    #include "globals.h"
#endif

void MyClass2::DoStuffToX()
{
    x *= static_cast<float>(my_name::myObject.GetI());
}

I try to compile this (all four files) and I get the following linker errors:

d:/dom/my documents/developing tools/temp programming/globalobjects/myclass2.o: In function `MyClass2:oStuffToX(void)':
//d/dom/my documents/developing tools/temp programming/globalobjects/myclass2.cpp:9: multiple definition of `my_name::myObject'
d:/dom/my documents/developing tools/temp programming/globalobjects/mymain.o(.bss+0x0)://D/DEV-C_~1/Include/G__~1/streambuf.h: first defined here

This is of course a simplified version of a much more complicated program, where I would really like to be able to have a global variable that can be included by more than one file. Any light on this would be much appreciated.

dt

Ahhahhh, thankyou. So would this be right?

Code:

#file1
...
namespace myNameSpace
{
   MyClass myObject(34);
}

#file2
...
extern myNameSpace::myObject(34);

Thanks again

dt

Having problems referring to the global in it's namespace. If I use:

Code:

using namespace myNameSpace;

The compiler quite rightly doesn't recognise the namespace (as it's in the .cpp and not included in any headers). And then I am baffled as to how to refer to my global. Have tried randomly:

Code:

extern MyClass myNameSpace::MyObject;

...and a few other combinations, to no avail. Anyone know how it's done??!



Another very related question: I would like the global to be an array. At the moment, I have set it as a pointer; then, when I want to initialize it I do something like:

Code:

extern MyClass myNameSpace::*MyObject;  // but obvioously not that!!!

myNameSpace::MyObject = new MyClass[100];
// myNameSpace::MyObject[0] = blah etc....

Once this is done, will the global be initialzed globally, so that whenever I rfer to it in another file (using extern) it will still contain the values I gave it in intitializing it. (I assume so, but this extern thing is confusing me!)

I did something similar in a project long ago... try something like this in your header file:

Code:

namespace myNameSpace
{
    extern MyClass MyObject;
}

Thanks guys