How do I prevent a class from being allocated via the 'new' operator? (I'd like to ensure my RAII class is always allocated on the stack.)

Question

I'd like to ensure my RAII class is always allocated on the stack.

How do I prevent a class from being allocated via the 'new' operator?

Answer 1

All you need to do is declare the class' new operator private:

class X
{
    private: 
      // Prevent heap allocation
      void * operator new   (size_t);
      void * operator new[] (size_t);
      void   operator delete   (void *);
      void   operator delete[] (void*);

    // ...
    // The rest of the implementation for X
    // ...
};  

Making 'operator new' private effectively prevents code outside the class from using 'new' to create an instance of X.

To complete things, you should hide 'operator delete' and the array versions of both operators.

Since C++11 you can also explicitly delete the functions:

class X
{
// public, protected, private ... does not matter
    static void *operator new     (size_t) = delete;
    static void *operator new[]   (size_t) = delete;
    static void  operator delete  (void*)  = delete;
    static void  operator delete[](void*)  = delete;
};

Related Question: Is it possible to prevent stack allocation of an object and only allow it to be instiated with ‘new’?