c++ - When should I use [[maybe_unused]]?

Question

What is good about using [[maybe_unused]]? Consider

int winmain(int instance, int /*prevInstance*/, const char */*cmdline*/, int show);

int winmain(int instance, [[maybe_unused]] int prevInstance, [[maybe_unused]] const char *cmdline, int show);

Some might insist that using comments is ugly, because this keyword was made and intended to be used under these circumstances, and I totally agree with it, but the maybe_unused keywords seems a bit too long to me, making the code slightly harder to read.

I would like to follow the standard as "strictly" as I can, but is it worth using?

Answer 1

If the parameter is definitely unused, [[maybe_unused]] is not particularly useful, unnamed parameters and comments work just fine for that.

[[maybe_unused]] is mostly useful for things that are potentially unused, like in

void fun(int i, int j) {
    assert(i < j);
    // j not used here anymore
}

This can't be handled with unnamed parameters, but if NDEBUG is defined, will produce a warning because j is unused.

Similar situations can occur when a parameter is only used for (potentially disabled) logging.