Question

Recently I found a piece of C++ code that effectively does the following:

char* pointer = ...;
const char* constPointer = const_cast<const char*>( pointer );

Obviously the author thought that const_cast means “add const”, but in fact const can be just as well added implicitly:

const char* constPointer = pointer;

Is there any case when I would really have to const_cast to a pointer-to-const (const_cast<const Type*> as in above example)?

Answer 1

const_cast, despite its name, is not specific to const; it works with cv-qualifiers which effectively comprises both const and volatile.

While adding such a qualifier is allowed transparently, removing any requires a const_cast.

Therefore, in the example you give:

char* p = /**/;
char const* q = const_cast<char const*>(p);

the presence of the const_cast is spurious (I personally think it obscures the syntax).

But you can wish to remove volatile, in which case you’ll need it:

char const volatile* p = /**/;
char const* q = const_cast<char const*>(p);

This could appear, for example, in driver code.