"The Art (and Science) of Using Global Variables Without Using Global Variables"

Method 1:

• Put a G_ or g_ in front of all your global variables.
• Declare them in global.h using the extern keyword.
• Define and initialize them in globals.cpp.
• Number of global variables: as many as you have.

Example:

        in globals.h:
        extern HINSTANCE G_hInst;

        in globals.cpp:
        #include <windows.h>
        #include "globals.h"
        HINSTANCE G_hInst = NULL;

        in program.cpp:
        #include <windows.h>
        #include "globals.h"
        ...
        
        WinMain( HINSTANCE hThisInst, ... )
        {
                G_hInst = hThisInst;
                ...
        }

        WndProc( ... )
        {
                ...
                ...  LoadBitmap( G_hInst, ... );
                ...
        }

Method 2:

• Put all global variables into a struct.
• Have a single global struct variable, using Method 1 rules.
• Number of global variables: one.

Example:

        in globals.h:
        struct tagGlobal
        {
                HINSTANCE hInst;
        };

        extern struct tagGlobal G;

        in global.c:
        #include <windows.h>
        #include "globals.h"
        struct tagGlobal G =
        {
                NULL    // HINSTANCE hInst
        };

        in program.cpp:
        #include <windows.h>
        #include "globals.h"
        ...
        
        WinMain( HINSTANCE hThisInst, ... )
        {
                G.hInst = hThisInst;
                ...
        }

        WndProc( ... )
        {
                ...
                ...  LoadBitmap( G.hInst, ... );
                ...
        }

Method 3:

• Put all global variables into a struct.
• Declare a single "global" function that returns either a pointer (C or C++) or a reference (C++ only) to the struct.
• Define the struct as a static variable inside the "global" function.
• Number of global variables: zero.

Example:

        in globals.h:
        struct tagGlobal
        {
                HINSTANCE hInst;
        };

        typedef struct tagGlobal GLOBAL, * LPGLOBAL;

        LPGLOBAL GetGlobalData( );

        in global.cpp:
        #include <windows.h>
        #include "globals.h"

        LPGLOBAL
        GetGlobalData( )
        {
                static GLOBAL data =
                {
                        NULL    // HINSTANCE hInst
                };
                return ( & data );
        }

        in program.cpp:
        #include <windows.h>
        #include "globals.h"
        ...
        
        WinMain( HINSTANCE hThisInst, ... )
        {
                LPGLOBAL lpG = GetGlobalData( );
                ...
                lpG->hInst = hThisInst;
                ...
        }

        WndProc( ... )
        {
                LPGLOBAL lpG = GetGlobalData( );
                ...
                ...
                ...  LoadBitmap( lpG->hInst, ... );
                ...
        }

Method 4 (C++ only):

• Put all the global variables into a pure static class as private static members.
• Write a public static accessor member function for each, that returns a reference to the variable.
• Make the constructor private.
• Number of global variables: zero.

Example:

        in Global.h:
        class CGlobal
        {
        private:
                static HINSTANCE m_hInst;

                CGlobal( ) { ; }        // pure static class

        public:
                static HINSTANCE & hInst( ) { return m_hInst; }

        };

        in Global.cpp:
        #include <windows.h>
        #include "Global.h"

        HINSTANCE CGlobal::m_hInst = NULL;


        in program.cpp:
        #include <windows.h>
        #include "Global.h"
        ...
        
        WinMain( HINSTANCE hThisInst, ... )
        {
                ...
                CGlobal::hInst( ) = hThisInst;
                ...
        }

        WndProc( ... )
        {
                ...
                ...  LoadBitmap( CGlobal::hInst( ), ... );
                ...
        }

Download example code (12K, zipped)

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