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[C++]Explain this to me

 
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Heartless
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PostPosted: Sun Jan 04, 2009 11:42 am    Post subject: [C++]Explain this to me Reply with quote
What is a singleton pattern? I read it in one of my books, but they did a bad job explaining it, and so did wikipedia.

Code:
class Singleton1
{
     public:
          Singleton1& Instance()
          {
               static Singleton Obj;
               return Obj;
          }
     private
          Singleton1();
}


What is Singleton1& Insatance(), Line 4.
I know it is declaring Instance as a function, what what is the Singleton1& part?

What is static Singleton Obj, Line 6.
What dose static do in there?

What is Singleton1(), Line 10?
What dose this private function do?
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HalfPrime
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PostPosted: Sun Jan 04, 2009 1:48 pm    Post subject: Reply with quote
Looks like it makes it so that you can only have 1 object of that class. When you try to make a second object, you get a pointer to the first instead.

If you did "Singleton a, b;", a and b would would just be pointers to the exact same object.

I've never heard of this before, though, so I may be wrong.

Static means that that variable is allocated once during the whole program so if it's called twice, it will be the same var.
msdn wrote:
When modifying a data member in a class declaration, the static keyword specifies that one copy of the member is shared by all instances of the class. When modifying a member function in a class declaration, the static keyword specifies that the function accesses only static members.


private means it can only be accessed by a member of that class. ie, you can't call a.Singleton1(); from the main loop. If it was under public:, then you could. There's also protected: which is like private:, but it cna also be accessed by members of child classes.
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