Singleton Correct Usage

[A.Russell]

Finding clear examples of singleton patterns isn't hard, but I am having trouble implementing them. Mainly, is there a way to set one at class level or am I completely off track?:

class SingletonUser
{
protected:
Singleton* singleton;

Public:
SingletonUser()
{
singleton = Singleton::GetInstance();
// error LNK2001: unresolved external symbol
// "private: static class Gravity * Gravity::m_instance"
}
}