Thread: Interface problem

Originally Posted by a.mlw.walker

Hi,
i am having trouble compiling my interface. I am trying to store a reference variable as a member variable of the interface object. Compiler says that the variable has not be initiated correctly.

O rly? Because everybody here has an idea what code you are working on and what that member variable is.

Interesting that you have been here for several years, and you still don't know how to describe your problem and how to post code in the code tags (I downloaded the code and it is sufficiently small to paste).

Originally Posted by a.mlw.walker

I pass the displayDriver object in when LCD is instantiated in main

o_O where is that "main"?

you can't initialize references that way. you have to do it in the constructor's initializer list.

Originally Posted by a.mlw.walker

Code:

class LCD : public VisualInterface {
public:
	LCD(DisplayDriver& displayDriver) : displayDriver(displayDriver) {}
}

also, I don't recommend having a parameter named the same as a data member.

Originally Posted by a.mlw.walker

Do you not see the member variable displayDriver in the interface VisualInterface?

Omg no, I don't. If you mention a non-existent main, you may as well mention a non-existent member variable. Is is so !$%!&$ hard to tell the variable name?

Originally Posted by a.mlw.walker

Do you mean like this:

Code:

LCD(DisplayDriver& displayDriver){this->displayDriver = displayDriver;}

?

no. I literally gave you the correct syntax in the example in my previous post.

Actually, Elkvis, your code is slightly wrong. You cannot initialize an inherited member in the initialiser list of a derived class, so it should be:

Code:

class VisualInterface
{
public:
    VisualInterface(DisplayDriver& DisplayDriver): m_DisplayDriver(DisplayDriver) {}
...
protected:
    DisplayDriver& m_DisplayDriver;
}
...
 
 
class LCD : public VisualInterface
{
public:
    LCD(DisplayDriver& DisplayDriver): VisualInterface(DisplayDriver) {}
}

There is no problem in having the driver as a pointer either, though, so long as you don't delete it. However, you should be aware that if you use a reference, you can't copy or assign the class unless you explicitly define a copy constructor and assignment operator. If you use a pointer, it will work, but you do have to think about if you really want the behaviour the default generated code does.

Originally Posted by Elysia

Actually, Elkvis, your code is slightly wrong. You cannot initialize an inherited member in the initialiser list of a derived class

you're right. I overlooked the inheritance.

The general rule is that you should avoid new (and thus, delete). There is nothing forbidding you to use pointers, if they are used correctly. There are things pointers can do that references cannot (for example, being rebound). Use the best tool for the job is the best answer. References are typically stronger than pointers, so I would say prefer them over pointers where possible.