Global Variable

First, you should ensure your include files are never included twice by putting that in our header. Also, you must ensure that interdependent classes don''t posses an instance of each others.


Use this first solution if your project is big, it will reduce dependencies.

#ifndef _MYHEADERFILENAME_H_
#define _MYHEADERFILENAME_H_
class MyClassName {
  //declarations go here.

};
#endif

Also, in dependent headers, avoid including .h as much as possible. Use forward declarations instead like this.

class MyClassName;
class MyDependentClass {
  MyClassName* blah; //you can also use a reference, but not an instance

}

---------
If your project is small, you can do that automatically in the header file and include the header in dependent headers, like this:

#ifndef _MYCLASSNAME_CLASS_
#define _MYCLASSNAME_CLASS_
class MyClassName;
#endif

#ifndef _MYHEADERFILENAME_H_
#define _MYHEADERFILENAME_H_
class MyClassName {
  //declarations go here.

};
#endif

However, this will create a LOT of dependencies and your whole project will recompile everytime you make a change in one .h

While Coincoin had a lot of good general advice, he didn''t really answer your question. If you really need to put a global in a header, this is what you do(exclusion guards etc omitted for brevity - see Coincoins post):

In the header:

extern int Global;
 

This tells the compiler that there is a variable named global, but that it shouldn''t allocate memory for it since it is declared elsewhere.

Then, in exactly *ONE* of the .cpp files - doesn''t really matter which:

// file1.cpp
int Global;
 

This will allocate the actual memory needed to hold that variable.

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Shame on me... I only read the part about the redefinition error.