Casting to derived type problem in C++
- by GONeale
Hey there everyone,
I am quite new to C++, but have worked with C# for years, however it is not helping me here! :)
My problem: I have an Actor class which Ball and Peg both derive from on an objective-c iphone game I am working on. As I am testing for collision, I wish to set an instance of Ball and Peg appropriately depending on the actual runtime type of actorA or actorB. My code that tests this as follows:
// Actors that collided
Actor *actorA = (Actor*) bodyA->GetUserData();
Actor *actorB = (Actor*) bodyB->GetUserData();
Ball* ball;
Peg* peg;
if (static_cast<Ball*> (actorA)) { // true
ball = static_cast<Ball*> (actorA);
}
else if (static_cast<Ball*> (actorB)) {
ball = static_cast<Ball*> (actorB);
}
if (static_cast<Peg*> (actorA)) { // also true?!
peg = static_cast<Peg*> (actorA);
}
else if (static_cast<Peg*> (actorB)) {
peg = static_cast<Peg*> (actorB);
}
if (peg != NULL) {
[peg hitByBall];
}
Once ball and peg are set, I then proceed to run the hitByBall method (objective c).
Where my problem really lies is in the casting procedurel Ball casts fine from actorA; the first if (static_cast<>) statement steps in and sets the ball pointer appropriately.
The second step is to assign the appropriate type to peg. I know peg should be a Peg type and I previously know it will be actorB, however at runtime, detecting the types, I was surprised to find actually the third if (static_cast<>) statement stepped in and set this, this if statement was to check if actorA was a Peg, which we already know actorA is a Ball! Why would it have stepped here and not in the fourth if statement?
The only thing I can assume is how casting works differently from c# and that is it finds that actorA which is actually of type Ball derives from Actor and then it found when static_cast<Peg*> (actorA) is performed it found Peg derives from Actor too, so this is a valid test? This could all come down to how I have misunderstood the use of static_cast. How can I achieve what I need? :)
I'm really uneasy about what feels to me like a long winded brute-casting attempt here with a ton of ridiculous if statements. I'm sure there is a more elegant way to achieve a simple cast to Peg and cast to Ball dependent on actual type held in actorA and actorB.
Hope someone out there can help! :)
Thanks a lot.
