Question

I have never written copy constructor, so in order to avoid pain i wanted to know if what i have coded is legit. It compiles but i am not sure that it works as a copy constructor should.

Also do i have to use const in the copy constructor or i can simply drop it. (What i dont like about const is that the compiler cries if i use some non const functions).

//EditNode.h
class EditNode
{
      explicit EditNode(QString elementName);
      EditNode(const EditNode &src);
}

//EditNodeContainer.h
class EditNodeContainer : public EditNode
{
      explicit EditNodeContainer(QString elementName);
      EditNodeContainer(const EditNodeContainer &src);
}

//EditNodeContainer.cpp
EditNodeContainer::EditNodeContainer(QString elementName):EditNode(elementName)
{
}       

//This seems to compile but not sure if it works
EditNodeContainer::EditNodeContainer(const EditNodeContainer &src):EditNode(src)
{

}


//the idea whould be to do something like this
EditNodeContainer *container1 = new EditNodeContainer("c1");
EditNodeContainer *copyContainer = new EditNodeContainer(container1);

Answer 1

A copy constructor is a constructor that has one of the following signatures:

class A
{
    A(A& other);
    //or
    A(const A& other);
    //or
    A(volatile A& other);
    //or
    A(const volatile A& other);
    //or any of the above + other parameters that have default arguments
    //example:
    A(const A& other, int x = 0) //this is also a copy constructor
};

The above is specified in 12.8.2 of the standard – C++03.
so you are implementing correctly a copy constructor.

The reason it should receive a const parameter is that you’re not changing the object you’re copying from. If you call non-const functions on it, you’re doing something wrong.

Also, in your snippet

EditNodeContainer *container1 = new EditNodeContainer("c1");
EditNodeContainer *copyContainer = new EditNodeContainer(container1);

you’re not calling a copy constructor, because you’re passing an EditNodeContainer* as parameter, not a EditNodeContainer.