c ++将指针传递给方法

Question

I have the following functions:

Triangle* operator=(Triangle& other) const
{
    for (unsigned int i = 0; i < other.getNumOfPoints(); i++)
    {
        this->addPoint(other.getPoint(i));
    }

    color = other.color;

    //type stays the same
    return this;
}


Point* Polygon::getPoint(int index) const
{
    return _points.at(index);
}

void Polygon::addPoint(Point* p) {
    Point* newp = new Point; //create a copy of the original pt
    newp->setX(p->getX());
    newp->setY(p->getY());
    _points.push_back(newp);
}

I am sure each understand what the objects mean, they are pretty straight forward. First method is located inside Triangle class which inherit from Polygon.

Problem is in the first method when I use

this->addPoint(other.getPoint(i));

Eclipse states its Invalid argument. Can I get an explanation of why is it error when getPoint returns Point pointer and AddPoint function requires a Point pointer?

Thanks in advance.

Answer 1

The problem is not about the Point* argument of addPoint , but about the implicit this pointer argument:

operator= is marked as a const function, so inside it, this is a pointer-to- const . Thus trying to call a non- const function on it doesn't work.

You need to mark operator= non- const .

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On a related note, you're also returning a pointer from operator= and taking the right-hand operand by non - const reference, both of which are weird things to do.

When overloading operators, it's strongly recommended to use the canonical signatures, which you can find eg here .