Question

I’ve got a function that takes a pointer to an object of a custom class (actually pointers to a base class such that polymorphism works). Within the calling routine this object however is exclusively needed for the purpose of this call, i.e. is temporary. For example like this:

class A { /** stuff */ };
class B : public A { /** stuff */ };

void doSomething( const A* const _p ) { /** stuff */ }

void callingRoutine()
{
  A* tempPointer = new B;
  doSomething( tempPointer );
  delete tempPointer;
}

Now, since I really only need the object of type B within the call to doSomething, is there a way to do it in one line? Doing

doSomething( new B );

creates memory leaks (valgrind says so). Or would

doSomething( &B );

be the recommended way? The latter compiles but gives warnings about passing pointers to temporary objects. This is what I want to do, but would it be safe this way?

Answer 1

The cleanest way is to do

B b;
doSomething(&b);

But what you really should write depends of what the doSomething function does. If it’s fine to destruct b at the end of callingRoutine, then it’s the faster and cleaner way to do this, because allocating on the stack is faster than new and does not require you to delete b afterwards.