Compile time check of whether a method defined as virtual

Question

I'm trying to come up with a way of checking in the derived class whether a method of the base class is defines as 'virtual' . Basically I would like to have the following code:

class A {
  virtual void vfoo() {}
  void foo() {}
  virtual ~A() {}
};

class B : public A {
  virtual void vfoo() {
    MAGIC_CHECK(m_pA->vfoo()); // succeed
    // code
    m_pA->vfoo();
    // code
  }
  virtual void foo() {
    MAGIC_CHECK(m_pA->foo()); // fail compilation because foo is not virtual!
    // code
    m_pA->foo();
    // code
  }
  A * m_pA;
};

The question is, how do I implement this MAGIC_CHECK? One solution for this could be using -Woverloaded-virtual compilation flag. Can anyone suggest a solution that will not involve this flag?

Thanks!

score 3 · Answer 1 · answered Mar 27 '12 at 13:10

3

In C++11 it's possible to add override at the end of the function declaration in the class and it will yield a warning if the function doesn't override anything:

class B : public A {
  virtual void vfoo() override { //OK
  }
  virtual void foo() override { //error
  }
};

answered Mar 27 '12 at 13:10

Luchian Grigore

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Will it check `virtual`ness also ? – iammilind Mar 27 '12 at 13:11
@iammilind oh, yes... it will break the build if the base method is not virtual. – Luchian Grigore Mar 27 '12 at 13:12
I mean suppose `A::foo()` and `B::foo()` matches the syntax, but they `A::foo()` is not declared as `virtual`, then will it give compiler error? I am asking, because I have less knowledge of this feature. – iammilind Mar 27 '12 at 13:14
@iammilind yes. See the link. – Luchian Grigore Mar 27 '12 at 13:14
Visual Studio has supported the `override` keyword since 2005. – IronMensan Mar 27 '12 at 14:41
Yes, I'm familiar with this feature in C++11. Assume I modify the requirement to something slightly different: Can I somehow check in compile time that the class A (in the example) is "interface"? By interface I mean that all its methods are pure virtual. Is this possible w/o C++11 features? – Vadim S. Mar 27 '12 at 17:16
1

@VadimS. not that I'm aware of. Might worth asking a new question. – Luchian Grigore Mar 27 '12 at 18:56

score 1 · Accepted Answer · answered Mar 27 '12 at 13:13

1

In C++03 standard, it's not possible to check if a method is declared as virtual or not.
You may follow,

coding standards
peer review
possibly some static analysis tool

answered Mar 27 '12 at 13:13

iammilind

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Compile time check of whether a method defined as virtual

2 Answers2

Linked