Question

class A
{
private:
    A(){}; 
    ~A(){};
public:
    static A* GetInstance( void )
    {
        static A obj;
        return& obj;
    }
};

I was supposing if something bad happens would only happen at the first time, since the class constructor is only initialized the first time a call to GetInstance happens, I don’t know the great depths of C++ and I do not trust C++, so when I need a pointer to this class that will be used many times in a function I’m currently doing:

A* ptr = A::GetInstance();
if( ptr )
{

Checking for the pointer validity, I believe that the method returns the address where the value of obj is stored so that ptr will point to it, which I guess it can't fail.

Please observe that I’m not talking about a small application, I’m currently developing on a 500,000+ lines MMO server application that handles thousand of clients and has to stay opened for weeks without crashing, defensive programming is the least minimum required. Is it for sure, 100% safe to use ptr without checking its validity?

Answer 1

There is certainly no way that that function will ever return a null pointer, so there’s no point checking for that. It might make more sense to return a reference, to make it clear that it won’t be null.

However, there’s no guarantee that the function will always return a pointer to a valid object. If it’s called from the destructor of a static object, then obj might already have been destroyed. This is one reason why globally accessible objects are a very bad idea, whether or not you wrap them up in the Singleton anti-pattern like this.