C++ Singleton Design Pattern Lazy Initialization
Example
This example has been lifted from the Q & A section here:http://stackoverflow.com/a/1008289/3807729
See this article for a simple design for a lazy evaluated with guaranteed destruction singleton:
Can any one provide me a sample of Singleton in c++?
The classic lazy evaluated and correctly destroyed singleton.
class S
{
public:
static S& getInstance()
{
static S instance; // Guaranteed to be destroyed.
// Instantiated on first use.
return instance;
}
private:
S() {}; // Constructor? (the {} brackets) are needed here.
// C++ 03
// ========
// Dont forget to declare these two. You want to make sure they
// are unacceptable otherwise you may accidentally get copies of
// your singleton appearing.
S(S const&); // Don't Implement
void operator=(S const&); // Don't implement
// C++ 11
// =======
// We can use the better technique of deleting the methods
// we don't want.
public:
S(S const&) = delete;
void operator=(S const&) = delete;
// Note: Scott Meyers mentions in his Effective Modern
// C++ book, that deleted functions should generally
// be public as it results in better error messages
// due to the compilers behavior to check accessibility
// before deleted status
};
See this article about when to use a singleton: (not often)
Singleton: How should it be used
See this two article about initialization order and how to cope:
Static variables initialisation order
Finding C++ static initialization order problems
See this article describing lifetimes:
What is the lifetime of a static variable in a C++ function?
See this article that discusses some threading implications to singletons:
Singleton instance declared as static variable of GetInstance method
See this article that explains why double checked locking will not work on C++:
What are all the common undefined behaviours that a C++ programmer should know about?
