Adding a body to a pure virtual / abstract function in C ++?

Question

A pure virtual function should not have a body, but I just noticed that the following code was accepted by the compiler:

class foo
{
    virtual void dummy() = 0
    {
        cout << "hello";
    }
};

So why do pure virtual functions allow you to have a body? Also, even if the function has a body, the class still cannot be created, why?

Answer 1

A pure virtual function may have a body, but the fact that you declare them pure virtual is to say that a derived implementation is required .

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Answer 2

, / . contract , , .

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...

virtual ~foo() = 0;

...

foo::~foo() {} // required!

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