Question

If DerivedClass1 and DerivedClass2 are classes derived from BaseClass, where BaseClass is a polymorphic class, which of these two code snippets are correct?

BaseClass *ptr;

ptr = new DerivedClass1;
ptr->PrintName();

ptr = new DerivedClass2;
ptr->PrintName();

delete ptr;

or

BaseClass *ptr;

ptr = new DerivedClass1;
ptr->PrintName();

delete ptr;

ptr = new DerivedClass2;
ptr->PrintName();

delete ptr;

Does using ‘new’ multiple times before using ‘delete’ simply redefine ptr’s value, or does it cause some kind of memory leak? Excuse me if this is a stupid question, but I couldn’t seem to find an answer to it.

Answer 1

Your first example will certainly leak. Your second example could leak, say if PrintName() threw an exception.

A better idea is to use a smart pointer, such as std::unique_ptr:

std::unique_ptr<BaseClass> ptr;

ptr.reset(new DerivedClass1);
ptr->PrintName();

ptr.reset(new DerivedClass2);
ptr->PrintName();

Look, Ma, no delete!