C/C++ :: Creating A Singleton Pointer?

I have a class in my application that only needs to be created once, but the object needs to be available to all other classes in my application if necessary. Since declaring everything static can be restrictive (as I understand), I created a class like this:

class Foo {
// Data members
// Constructor/Destructor
// Functions
};
extern Foo* myFoo = new Foo();

And then the global variable gets deleted at the very end of the main method when everything is done:

#include "Foo.cpp" // (yes, I know this is normally bad, this is how I'm required to code)
int main() {
// do stuff
delete myFoo;
return 0;
}

These won't link, though, because I get undefined reference linking errors to myFoo wherever I use it. I'm pretty sure this means I'm creating a singleton wrong, but I'm not sure what I'm doing wrong -- there's no const conflicts and the pointer is properly initialized (to my understanding). If there's a better way to do this than extern, I'm completely open to it, as long as it's understandable and works.