C++ header files and variable scope

I want to organize my c++ variables and functions in the following way: function prototypes in a header file "stuff.h", function implementation in "stuff.cpp", then say #include "stuff.h" in main.cpp (so I can call functions implemented in stuff.cpp). So far so good. Now I want to declare some variab开发者_运维百科les in stuff.cpp that have global scope (so I can modify the variables in functions implemented in stuff.cpp and main.cpp). This doesn't seem to work. How can I do this?

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Declare them as extern. E.g., in stuff.h:

extern int g_number;

Then in stuff.cc:

int g_number = 123;

Then in main.cc just #include stuff.h.