How to write a macro that discards the const qualifier, for any type?

I hope some combination of typeof and a cast will do, but haven't found the combination.

I tried this, without luck:

#define discard_const(_x)  ((typeof(_x + 0)) (_x))

struct t {
    char *s;
};

char *
foo(const struct t *r)
{
    return discard_const(r->s);
}

I also tried: #define discard_const(_x) ({__auto_type _y = (_x); _y;}), but not luck

The objective is that if I cast to (char *), I fear that if the type of s changes in the future, the cast might silence any warnings, so I want the type to be automatically calculated, and I only want to discard const.

Of course, with pragmas I may disable any const warnings for that specific line, but a macro that does it within the language would be nicer.

posted almost 2 years ago

CC BY-SA 4.0

2y ago

alx‭

447 reputation 13 6 76 108