Re: [boost] dangerous_cast<>

From: Gabriel Dos Reis (gdr_at_[hidden])
Date: 2002-12-04 10:38:32

David Abrahams <dave_at_[hidden]> writes:

| Gabriel Dos Reis <gdr_at_[hidden]> writes:
| 
| > "David B. Held" <dheld_at_[hidden]> writes:
| >
| > | Does this have any merit whatsoever?
| > | 
| > | template <typename T, typename U>
| > | T* dangerous_cast(U* p)
| > | {
| > |     return static_cast<T*>(static_cast<void*>(p));
| > | }
| >
| > Is it any different from reinterpret_cast<T*>(p) ?
| 
| It might be, depending on your compiler. The behavior of
| reinterpret_cast<T*> is implementation-defined.

The mapping used by reinterpret_cast<> is implementation defined,
thus an implementation is required to document it.

 1) Do you have any corresponding guarantee for converting a void* to
    T* when the source is *not* a T* nor the address obtained from a T?

 2) Isn't the mapping U* -> void* -> T* at best
    implementation-defined if not undefined behaviour? 

-- Gaby