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c++inheritancepure-virtual
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Reputation: 4954

Changing inherited function to be pure virtual

I'm wondering if the following is possible. I wanted my derived class dA to change func() to be pure virtual so that any classes derived from dA must implement func().

Code similar to below compiles without complaint under MSVC even though ddA does not implement func().

The compiler does complain about the below code (see comments). So my question now becomes: is this a standards-compliant way to achieve what I want?

class A {
   public:
      virtual void func() { /* Some base implementation. */ }
}

class dA : public A {
   public:
      void func() override = 0;   // Is this valid?
}

class ddA : public dA {
}

Upvotes: 1

Views: 206

Answers (1)

Saeed All Gharaee
Saeed All Gharaee

Reputation: 1693

Pure virtual function should be declared in parent class. Consider the code below: '''

class Shape {
public:
    Shape(int init_x, int init_y) : x(init_x), y(init_y) {}

    virtual void scale(int s) = 0;
    virtual void print() = 0;
protected:
    int x;
    int y;
};

These functions should be implemented in children:

class Rect : public Shape {
public:
    Rect(int init_x, int init_y, int w, int h);
    virtual void scale(int s) { //implementation }
    virtual void print() { //implementation }
private:
    int width;
    int height;
};

However you don't have to implement virtual functions in subclasses since it had been implemented in super class:

Pure virtual function make your class abstract so you can't use its instances.

Upvotes: 1

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