C++ method only visible when object cast to base class?

Question

It must be something specific in my code, which I can't post. But maybe someone can suggest possible causes.

Basically I have:

class CParent
{
 public:
  void doIt(int x);
};
class CChild : public CParent
{
 public:
  void doIt(int x,int y,int z);
};

CChild *pChild = ...
pChild->doIt(123); //FAILS compiler, no method found
CParent *pParent = pChild;
pParent->doIt(123); //works fine

How on earth?

EDIT: people are talking about shadowing/hiding. But the two versions of doIt have different numbers of parameters. Surely that can't confuse the compiler, overloads in child class which can't possibly be confused with the parent class version? Can it?

The compiler error I get is: error C2660: 'CChild::doIt' : function does not take 1 argument

Answer 1

You have shadowed a method. For example:

struct base
{
    void method(int);
    void method(float);
};

struct derived : base
{
    void method(int);
    // base::method(int) is not visible.
    // base::method(float) is not visible.
};

You can fix this with a using directive:

class derived : public base
{
    using base::method; // bring all of them in.

    void method(int);
    // base::method(int) is not visible.
    // base::method(float) is visible.
};

---

Since you seem insistent about the number of parameters, I'll address that. That doesn't change anything. Observe:

struct base
{
    void method(int){}
};

struct derived : base
{
    void method(int,int){}
    // method(int) is not visible.
};

struct derived_fixed : base
{
    using base::method;
    void method(int,int){}
};

int main(void)
{
    {
        derived d;

        d.method(1, 2); // will compile
        d.method(3); // will NOT compile
    }
    {
        derived_fixed d;

        d.method(1, 2); // will compile
        d.method(3); // will compile
    }
}

It will still be shadowed regardless of parameters or return types; it's simply the name that shadows. using base::<x>; will bring all of base's "<x>" methods into visibility.

Answer 2

You are hitting a classic problem. You need using CParent::doIt; in your CChild class. I'll scrounge up the duplicate questions.

Edit:

Here's my answer to essentially the same question: Overriding a Base's Overloaded Function in C++