使用 static_cast 投射 POD 对象

Question

this is what i mean,

class V3
{
public:
float x,y,z;
};

class V3_
{
 public:
float x,y,z;
};

V3_ vec1;
V3 vec2 = static_cast<V3_>(vec1);

what should i do to make this cast work in compile time?

Thanks.

edit:

there seems to be some misunderstanding about what i want to do. i can write an operator to the conversion, but i want it to be done in compile time.

here are two implementations of Vector3 that allows static_cast. i dont know how does it work, but it does work.

http://www.ogre3d.org/docs/api/html/OgreVector3_8h_source.html

http://harry-3d-engine.googlecode.com/svn/trunk/NxOgreVec3.h

i can do this cast

 void DynamicBody::SetLinearMomentum(const Vector3& vel)
 {
body->setLinearMomentum(static_cast<NxOgre::Vec3>(vel));
 }

i would like an explanation on how i can do this.

edit:

upon further investigation i found how it actually does this, it calls

template<class user_xyz_vector_type>
inline user_xyz_vector_type as() const { ... }

that is not an actual static_cast, but compiler accepts it as one. i really hoped casting pods to eachother was an actual thing.

Answer 1

This cast will not work at any time. You can't static_cast completely unrelated and not convertible types to each other.

I'm not sure what you are trying to do, so I don't know what the work "work" means in this case, but at a raw memory level the conversion can be performed by reinterpret_cast

V3 vec2 = reinterpret_cast<V3_&>(vec1);

but this is an ugly hack that is not guaranteed to work, since, again, your types are unrelated. With the same degree (or even better) of success you can simply memcpy one object into another.

Answer 2

You could avoid using cast altogether as:

V3 vec2 = {vec1.x, vec1.y, vec1.z};

Or write conversion function:

V3 to_V3(V3_ const & v)
{
   V3 v3 = {v.x, v.y, v.z};
   return v3;
}

and use it as:

V3 vec2 = to_V3(vec1);

Answer 3

The types are unrelated, therefore you need reinterpret_cast :

V3_ vec1;
V3 vec2 = reinterpret_cast<V3_&>(vec1);

Answer 4

V3_ vec1;
V3 vec2 = *(V3*)&vec1;

EDIT: still, you know that's probably not a good thing to do?

Answer 5

To static_cast V3 to V3_ use public: on V3 class declaration. class V3 : public V3_ . This way you can convert objects. Use virtual deconstructors if you want polymorphism and you're aware of what you're doing.