C++ downcasting

Question

This question is a followup on what I posted here

Synth implements Generator and Track has a generator member (which has a Synth in it). What I want to do is something like:

Track track = Track();
cout << track.generator.varA << endl;

But this doesn't work so I'm guessing I have to somehow cast generator to Synth first, before I can access any synthesizer methods or members and I can't figure out how to do that.

Answer 1

在确定您拥有的基本指针确实是该派生类型时，要将其转换为派生类型，请执行以下操作：

static_cast<Derived*>(myBasePointer)

Answer 2

First of all, generator is a pointer, so you cannot use the . operator to access a member of the pointed object, as you do here:

track.generator.varA // ERROR!

Secondly, since you want a pointer to a derived class and you have a pointer to a base class, you should use dynamic_cast<> to get one (unless you are sure the object pointed to is an instance of the derived class, in that case you can use static_cast<> ):

Synth* p = dynamic_cast<Synth*>(track.generator);
if (p != nullptr)
{
    cout << p->varA << endl;
}