C++ basic constructors/vectors problem (1 constructor, 2 destructors)

Question

Question is probably pretty basic, but can\'t find out what\'s wrong (and it leads to huge of memleaks in my app):

class MyClass {
public:
    MyClass() { co         


        

Answer 1

When the b object gets pushed onto the vector a copy is made, but not by the operator=() you have - the compiler generated copy constructor is used.

When the main() goes out of scope, the b object is destroyed and the copy in the vector is destroyed.

Add an explicit copy constructor to see this:

MyClass( MyClass const& other) {
    cout << "copy ctor\n";
};

Answer 2

If you want to log all copies and constructions you should add an explicit copy constructor so that the compiler doesn't create one for you.

MyClass( const MyClass& )
{
    cout << "Copy constructor\n";
}

You can, in your copy constructor, call your assignment operator. It is a reasonably common way of implementing things, however with your definition of operator=, this may have serious problems.

You have an unconventional implementation of operator=. operator= should return a reference to the class on which it is called (to enable proper chaining), but you return a new class instance by value. This means that if you tried to call operator= from your copy constructor you may well end up with infinite recursion. Try this operator= instead:

MyClass& operator=( const MyClass& )
{
    cout << "operator=\n";
    return *this;
}

When defining an assignment operator you should always consider the possibility that the parameter and *this may refer to the same object and ensure that the definition of the operator won't have any unintended effects in this scenario.