CODEWITHSUNDEEP
c++
Andrei
Andrei

Reputation: 8914

Making sure the method declaration is inherited

How can I protect from accidental definition of non-inherited method where inherited definition is intended. I am told there is trick to express it, but nobody can recall it.

Explanation. I have tree of classes: 'Base' <- 'C' <- 'D', below. Base defines pure virtual function. The function gets redefined in C then in D. But the function has very long argument list.

Somewhere along chain of derivation, there is subtle error in the agrglist which makes D:: non-inherited. Program hapily compiles. And the wrong method is called in the run-time.
Is there trick to cause compilation error when method is non-inherited.

#include <iostream>

class Base {
public:
    virtual void VeryLongFunctionName(int VeryLongArgumentList) = 0;
};
class C : public Base {
public:
    void VeryLongFunctionName(int VeryLongArgumentList) {
        std::cout << "C::\n";
    }
};
class D : public C {
public:
    void VeryLongFunctionNane(int VeryLongArgumentList) { // typo is intentional. It's the point of the question.
        std::cout << "D::\n";
    }
};

int main() {
    Base *p = new D;
    p->VeryLongFunctionName(0);
            // the intention is to print D::. But it prints C::.
            // How can we make compiler catch it.       
    return 0;
}

Upvotes: 5

Views: 209

Answers (3)

ildjarn
ildjarn

Reputation: 62995

For this exact purpose C++0x introduces the override member function decorator, as is already implemented in VC++ 2005 and later: http://msdn.microsoft.com/en-us/library/41w3sh1c.aspx

Alternatively, VC++ permits the following (presumably compiler-specific):

#include <iostream>

class Base {
public:
    virtual void VeryLongFunctionName(int VeryLongArgumentList) = 0;
};

class C : public Base {
public:
    void Base::VeryLongFunctionName(int VeryLongArgumentList) {
        std::cout << "C::\n";
    }
};

class D : public C {
public:
    void Base::VeryLongFunctionNane(int VeryLongArgumentList) {
    //   ^^^^^^ now causes a compilation error
        std::cout << "D::\n";
    }
};

Upvotes: 2

justin
justin

Reputation: 104708

not exactly what you asked for, but i've used this form to reduce the chance for human error:

class t_very_long_argument_list {
public:
    t_very_long_argument_list(T1& argument1, const T2& argument2);
    /* ... */
    T1& argument1;
    const T2& argument2;
};

int C::VeryLongFunctionName(t_very_long_argument_list& arguments) {
    std::cout << "C::\n";
}

Upvotes: 4

Mahesh
Mahesh

Reputation: 34625

You have compilation errors -

  • int VeryLongFunctionName(int VeryLongArgumentList) supposed to return an int which none of the method definitions is doing so.

  • int VeryLongFunctionName(int VeryLongArgumentList) supposed to receive an int.

    p->VeryLongFunctionName(); // Error

With these corrected, you should get the expected results. Check results : http://ideone.com/wIpr9

Upvotes: 1

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