Why do we have reinterpret_cast in C++ when two chained static_cast can do it's job?
- by Nawaz
Say I want to cast A* to char* and vice-versa, we have two choices (I mean, many of us think we've two choices, because both seems to work! Hence the confusion!):
struct A
{
int age;
char name[128];
};
A a;
char *buffer = static_cast<char*>(static_cast<void*>(&a)); //choice 1
char *buffer = reinterpret_cast<char*>(&a); //choice 2
Both work fine.
//convert back
A *pA = static_cast<A*>(static_cast<void*>(buffer)); //choice 1
A *pA = reinterpret_cast<A*>(buffer); //choice 2
Even this works fine!
So why do we have reinterpret_cast in C++ when two chained static_cast can do it's job?
Some of you might think this topic is a duplicate of the previous topics such as listed at the bottom of this post, but it's not. Those topics discuss only theoretically, but none of them gives even a single example demonstrating why reintepret_cast is really needed, and two static_cast would surely fail. I agree, one static_cast would fail. But how about two?
If the syntax of two chained static_cast looks cumbersome, then we can write a function template to make it more programmer-friendly:
template<class To, class From>
To any_cast(From v)
{
return static_cast<To>(static_cast<void*>(v));
}
And then we can use this, as:
char *buffer = any_cast<char*>(&a); //choice 1
char *buffer = reinterpret_cast<char*>(&a); //choice 2
//convert back
A *pA = any_cast<A*>(buffer); //choice 1
A *pA = reinterpret_cast<A*>(buffer); //choice 2
Also, see this situation where any_cast can be useful: Proper casting for fstream read and write member functions.
So my question basically is,
Why do we have reinterpret_cast in C++?
Please show me even a single example where two chained static_cast would surely fail to do the same job?
Which cast to use; static_cast or reinterpret_cast?
Cast from Void* to TYPE* : static_cast or reinterpret_cast
