Constants in derived classes 1

[timmay3141]

I am writing a program where I will have a base class with an int that should stay constant, and derived classes that will have their own unique values. For example, it would be something like this:

class BaseClass
{
public:
const int num;
BaseClass() : num(0) {};
};

class DerivedClass : public BaseClass
{
DerivedClass() : num(1) {};
}

Basically, I want all of the derived classes to have their own unique values for num. Unfortunately, this won't compile without making num a non-const integer, because you must initialize constants in the initialization list of the base class. Is there any way I could get around this but leave num as a const?

 

[onlyshiza]

well, why you want to make that varible constant? As you said you are not able to change the value assigned to a constant, otherwise it wouldn't be constant anymore!...

 

[timmay3141]

I see what you are saying, but once I initialize it, it should never be changed. It really doesn't matter, as long as I just make sure I don't accidentally change it somewhere. I just wanted to make it a const so I couldn't accidentally change it.

 

[PerFnurt]

Here's one way:

class BaseClass
{
protected:
BaseClass(int n) : num {};
private:
const int num;
};

class DerivedClass : public BaseClass
{
public:
DerivedClass() : BaseClass(1) {};
}

Note the protected constructor ie can only be called from a derived class.



[sub]Nerdy signatures are as lame as the inconsistent stardates of STTNG.[/sub]

 

[timmay3141]

Great, that's what I needed. Have a star.