Declare and define static variable in C++ header?

Question

Many other questions deal with how to allocate a variable by declaring it in a header file and defining it (allocating) in a .cpp file.

What I want to do is not use any .cpp files for my class, and to define all functions as inline (in the header file). The problem that I run into is how to define static member variables so that even when the .h file is included in multiple compilation units I don't get the "first defined here" linker error.

I'm open to preprocessor hacks, etc. if it gets the job done. I just want to avoid any .cpp files.

If it matters I'm using GCC.

Answer 1

You can abuse the singleton pattern if you really must avoid any .cpp files:

class Foo {
    public:
        static Bar& getMyStatic() {
            static Bar bar;
            return bar;
        };
};

This works because now the variable is a static variable inside a function, and static has a different meaning within a function context than within a class context. And for functions, the linker does recognize multiple identical definitions and throws away the copies.

But, of course, I would strongly advise against avoiding .cpp files: It means that you get into a situation where you have to build the entire program, or at least large parts of it, in one big piece. Every change you do will necessitate a complete rebuilt which slows down your change-compile-test cycle significantly. For very small projects that might not be a problem, but it is for medium to large ones.