Correct usage(s) of const_cast<>

it is pretty much designed to be only used with legacy APIs that are not const correct i.e. with a function you can't change that has non const interface but doesn't actually mutate anything on the interface

Like others have said, its primary purpose is to remove const from objects in order to pass to non-const correct functions you know won't modify the argument.

There is a trick (by Meyers?) to avoid code duplication, and it goes like this:

struct foo
{
    const return_type& get(void) const
    {
        // fancy pants code that you definitely
        // don't want to repeat

        return theValue; // and got it
    }

    return_type& get(void)
    {
        // well-defined: Add const to *this,
        // call the const version, then
        // const-cast to remove const (because
        // *this is non-const, this is ok)
        return const_cast<return_type&>(static_cast<const foo&>(*this).get());
    }
};

const_cast is also used to remove volatile modifiers, as put into practice in this (controversed) article:

http://www.drdobbs.com/184403766