Visual C++ - reinterpret_cast
We use reinterpret_cast to convert from one data type to different data type which are mainly used for storing and retrieving. For example, converting a pointer object to a long value is called reinterpret_cast.
A commonly used example in MFC would be a CListCtrl consisting of many items and each item needs to be associated with a class pointer to store its properties, then we use CListCtrl::SetItemData and CListCtrl::GetItemData. Note that this function takes the DWORD as argument. We can pass a class member pointer as DWORD by converting using reinterpret_cast.
In this example, we are converting the pointer objects p1, p2, p3 to unsigned long values lValue1, lValue2, lValue3. And we are converting back the unsigned long value to Shape* pointer objects s1, s2, s3. Then we are checking whether s1 == p1 && s2 == p2 && s3 == p3.
Source Code
class Shape
{
public:
Shape()
{
std::cout << "Shape\n";
}
virtual void draw() = 0;
};
class Rect1 : public Shape
{
int l,b;
public:
Rect1()
{
std::cout << "Rectangle\n\n";
}
virtual void draw() {}
};
class Circle : public Shape
{
int r;
public:
Circle()
{
std::cout << "Circle\n\n";
}
virtual void draw() {}
};
class Square : public Shape
{
int a;
public:
Square()
{
std::cout << "Square\n\n";
}
virtual void draw() {}
};
int _tmain(int argc, _TCHAR* argv[])
{
Shape *p1 = static_cast (new Rect1());
Shape *p2 = static_cast (new Circle());
Shape *p3 = static_cast (new Square());
unsigned long lValue1 = reinterpret_cast(p1); // casting to unsigned long
unsigned long lValue2 = reinterpret_cast(p2); // casting to unsigned long
unsigned long lValue3 = reinterpret_cast(p3); // casting to unsigned long
Shape *s1 = reinterpret_cast(lValue1); // casting back to Shape*
Shape *s2 = reinterpret_cast(lValue2); // casting back to Shape*
Shape *s3 = reinterpret_cast(lValue3); // casting back to Shape*
if( s1 == p1 &&
s2 == p2 &&
s3 == p3)
{
std::cout << "reinterpret_cast is Successfull\n\n";
}
return 0;
}
Output
reinterpret_cast is Successfull
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