Basides declaring game, you also have to define it once using Cmatrix game;. GL errors should be solved by linking opengl32.lib.

It''s not enoogh to declare variables, you have to define them as well. A declaration basically tells the compiler that there is an entity with said name and properties, and that it is stored elsewhere. Definition is the same as declaration, but additionally it allocates storage for the variable. Each variable must be defined (without extern) once for your project.

Suppose that in your header file you declare a global variable so that all .cpp files that #include it can refer to it, i.e.

extern int iGlobalInt; 

You must then also define it in one of the .cpp files. The ''extern ...'' just says that there is such a variable so that all the other .cpp files can refer to it (legally). It doesn''t create it (or rather, define it); this is your responsibility. Thus in one of your .cpp files (whichever should be responsible for creating it) you will put

int iGlobalInt /* = whatever */; 

Let''s say you have a variable int GlobalFlag; that you want to be shared among two source files. Naturally, you use a header file that _declares_ this variable:

quote:globals.h

extern int GlobalFlag;

This line specifies that there is a variable with the name GlobalFlag of type int that is stored "elsewhere". The linker, not the compiler, puts variables and functions together and looks for unresolved as well as duplicate variables. The compiler just stores the fact that GlobalFlag is defined somewhere else. It, however, knows how to use GlobalFlag.

Now you have two source files that both use this variable;

quote:source.cpp and source2.cpp
#include "globals.h"
// Now we know that there exists a variable GlobalFlag of type int, use it
GlobalFlag = 2;

Note that both cpp files don''t know where the variable is stored. If you _defined_ it in both cpp files, each file tries to access its own GlobalFlag:

quote:source.cpp and source2.cpp
int GlobalFlag;
// Accesses each own cpp''s GlobalFlag, not the only common one
GlobalFlag = 2;

Using a declaration enables both cpp files use a variable that is "external" (not defined in either of them). However, the linker must have _definitions_ for everything you use. You have to have one, and only one, _definition_ of GlobalFlag. So, in one of your source files, you add

quote:either source.cpp or source2.cpp
int GlobalFlag;

Now one source file allocates storage for the GlobalFlag variable, while the other one uses that storage. To the second file, GlobalFlag is "external" because it''s defined in another file.

If you ask a specific questions, you might get a more useful anwer.

quote:Original post by Oluseyi
Organizing Code Files in C and C++.

He already read this. Look at the original post.