uibk_703807-Advanced-CXX/topic/little_features/pointer_to_member.cpp

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2021-01-21 15:08:19 +01:00
#include <cassert>
struct Point {
float x, y;
};
struct Rect {
Point tl, br;
float area() const { return (br.x - tl.x) * (br.y - tl.y); }
};
class IShape {
public:
virtual float area() const { assert(false); };
virtual ~IShape() {}
};
class Square : public IShape {
public:
Square(float extend) : m_extend(extend) {}
float area() const override { return m_extend * m_extend; }
private:
float m_extend;
};
int main()
{
Rect r1{{1, 1}, {4, 4}};
assert(r1.area() == 9.0f);
Rect *r1_ptr = &r1;
assert(r1_ptr->area() == 9.0f);
// pointer to member variable
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auto tl_mem_ptr = &Rect::tl; // Point Rect::*tl_mem_ptr
assert((r1.*tl_mem_ptr).x == 1.0f);
assert((r1_ptr->*tl_mem_ptr).x == 1.0f);
// pointer to member function
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auto area_memfn_ptr = &Rect::area; // float (Rect::*area_memfn_ptr)() const
assert((r1.*area_memfn_ptr)() == 9.0f);
assert((r1_ptr->*area_memfn_ptr)() == 9.0f);
// Virtual
Square square{2.0f};
IShape *shape_ptr = &square;
// virtual member function pointer
auto virt_area_memfn_ptr = &IShape::area; // float (IShape::*virt_area_memfn_ptr)() const
assert((square.*virt_area_memfn_ptr)() == 4.0f);
assert((shape_ptr->*virt_area_memfn_ptr)() == 4.0f);
}