What are the type-casting types?

Question

Ive seen static_cast, dynamic_cast or reinterpret_cast but i dont know the difference between them.

Answer 1

Hi Garme, the different cast operators do different types of conversion:

* static_cast: checked conversion between types of similar nature (e.g. int and float) at compile time
* dynamic_cast: a checked conversion between pointers to classes at runtime
* const_cast: let's you change the const modifier of a type at compile time
* reinterpret_cast: unchecked conversion at compile time from an arbitrary type to another arbitrary type (the compiler does not check if this can be converted, it just interprets the same data in a new way); pls prevent the use of reinterpret_cast, if you can, as this can lead to really nasty problems. Nevertheless, this operator is mostly useful in programming on a low level, i.e. on hardware or almost on hardware.

Some examples:
// static_cast
float a = 10;
int b = static_cast<int>(a);

// dynamic_cast
class A {};
class B: public A {};
class C: public A {};
A* pca = new B();
B* pcb = dynamic_cast<B*>(pca); // ok
C* pcc = dynamic_cast<C*>(pca); // exception, pca does not refer to a C, it refers to a B

// const_cast
const int c = 11;
int &d = const_cast<int>(c);
const float e = const_cast<const float>(a);

// reinterpret_cast
C* f = reinterpret_cast<C*>(a); // float -> C*, ouch

To be completely honest, there's a fifth cast operator which was the only one initially in C++, as it is taken from C++s predecessor, C. This operator is equivalent to the reinterpret_cast operator.
Example:
C* f = (C*)a; // float -> C*, still ouch :-)

Please don't use the C casting operator at all, as the above mentioned four operators can do every type conversion you will ever need and restrict the conversion to a more specific purpose. This prevents some unintended effects and also states more explicitly what kind of conversion you actually want to do (makes it more readable).

Answer 2

I don't understand, why did you write int &d, what is the meaning of it?

Answer 3

&d means that d is an alias for the term on the right side of the equals sign.
A bit of a stripped-down example :
int a = 5;
int &b = a;

Answer 4

Okok, I realize, I did not answer your question. :-) I did it to have some variety as the example is quite long. :-)

Answer 5

Ok thx!

Answer 6

My pleasure :-)