c++ - How to cast pointer to base type conditionally given a pointer to derived type -

c++ - How to cast pointer to base type conditionally given a pointer to derived type -

i have 2 derived classes, triangle , sphere, base of operations class shape.

i have situation stored base of operations class pointer, shape* in class a, , have 2 overloaded fellow member functions of class a each derived type, dosomething(sphere* sp) , dosomething(triangle* tr).

class shape { public: shape() {}; virtual ~shape() = 0; }; class triangle : public shape { public: triangle(); }; class sphere : public shape { public: sphere(); }; class { private: shape* shape; void dosomething(triangle* tr); void dosomething(sphere* sp); public: a(); ~a(); };

however, when seek run code passing pointer of type shape* dosomething function, next error:

candidate function not viable: cannot convert base of operations class pointer 'value_type' (aka 'shape *') derived class pointer 'const triangle *' 1st argument void a::dosomething(triangle* tr) {

and same message sphere. i'm sure although pointer of type shape *, points 1 of derived objects.

so, how resolve issue preferably without modifying triangle , sphere classes , modifying a?

there's no way in c++. way dynamic dispatch phone call virtual method:

shape->dosomething();

where maybe triangle::dosomething , sphere::dosomething different implementations of virtual shape::dosomething.

so either need alter code construction it's shape controls calling. or... can have massive branch seek each 1 in turn:

void dosomething() { if (triangle* t = dynamic_cast<triangle*>(shape)) { dosomething(t); } else if (sphere* s = dynamic_cast<sphere*>(shape)) { dosomething(s); } // etc. }

i recommend not doing though. in additional beingness awful read, it's slow , unmaintainable.

c++ pointers casting