Re: Cast "const char *" pointers to "char *" to avoid compiler warnings.

[Jeffrey Walton <noloader at gmail dot com>]

On Tue, Oct 2, 2018 at 5:10 AM Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>...  (In a very quick look at locale.c, for example,
> > locale can definitely be written to--it is definitely not const. This implies
> > that the const on new_locale is what is wrong.)
>
> I did have this "very quick look at locale.c" before writing the
> patch, and not adding
> the cast at the assignment point means removing "const" from __loadlocale()
> prototype:
> char *__loadlocale (struct __locale_t *loc, int category, const char
> *new_locale)
> which in turn has a significant impact on the callers which I hope
> people familiar
> with this area can confirm, or not.

As I understand it, you can only cast const away if the [original]
object is in fact non-const.

OK:

    void foo(const char* buff)
    {
        ((char*)buf)[0] = '\0';
    }

    char bar[10] = {0};
    foo(bar);

Not OK:

    void foo(const char* buff)
    {
        ((char*)buf)[0] = (char)1;
    }

    const char bar[10] = {0};
    foo(bar);

The tricky part is finding the original object.

I don't know if there is a sanitizer to help find these violations,
but I have often wondered about one.

Jeff