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I will start with what's most of us already know:

If I want my class to be abstract, I must define at least one of its methods as "pure virtual", for example, here, the method someFunction() is defined as "pure virtual", as it is defined with the virtual keyword and it is assigned with 0:

class SomeClass {
    virtual void someFunction() = 0;
};

My question is, when I want an "abstract class", i.e. a class which cannot be instantiated (like "pure virtual" class), but I want to implement all its methods. Is there any standard way to do it?

My current workaround is ugly - I just define another dummy pure virtual method:

class UglyWorkaround {
    public:
        virtual void doAction1();
        virtual void doAction2();

        // My ugly workaround for making the class abstract - defining a dummy method
        virtual void thisIsADummyMethod() = 0;
};

This is very bad, as any deriving non-abstract class will have to implement it

Is there a more standard/popular way to define and implement such a class?

I want to clarify - I don't want another ugly workaround - I ask whether there is any standard way that is commonly used. The objective is to make the code readable for other programmers, so they immediately understand that the class is abstract

SomethingSomething
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1 Answers1

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Define the constructor protected

fjardon
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  • It sounds nice on first thought, but it won't prevent you from creating instances of your class from within its methods – SomethingSomething Oct 26 '15 at 13:59
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    @SomethingSomething, if the methods are not static, then how do you invoke them? If they are static, then they are most likely factory methods that should be able to call the ctor. C++ cannot read the mind of the programmers. If they do something wrong, then the program will do exactly the wrong think it was asked to do. – Kijewski Oct 26 '15 at 14:07
  • I agree. If your methods are `not` static, they won't be able to run, as you should have an instance which no one could create. But if your methods `are` static, then someone can run them and they can create instnaces . I want the class to be totally "abstract", like a class that is defined in Java with the "abstract" keyword. I want to block any try to instantiate it not by a child's constructor – SomethingSomething Oct 26 '15 at 14:10
  • Would `#define ABSTRACT /*void*/` for e.g. `ABSTRACT class Animal {...};` work for you? – Kijewski Oct 26 '15 at 14:18