assert return-value, but run either way

Question

Typically, when I erase an element from a set, I want to assert that it was actually erased: ie

assert(s.erase(e));

but then the element doesn't get erased when NDEBUG is set. But if I write

bool removed = s.erase(e);
assert(removed);

the compiler complains that 'removed' is unused when NDEBUG is set.

How can I do this right?

I ended up just creating a utility method:

inline void run_and_assert(bool b) {
    assert(b);
}

now I can say

run_and_assert(s.erase(e));

Are there any drawbacks to this? It seems simpler to me than luiscubal's solution

Many compilers provide a `verify()` function/macro that does what you want. — Jonathan Wood, Dec 17 '13 at 20:56
the very obvious drawback is now you get told only that `b` failed, instead of whatever condition you were actually asserting... — underscore_d, Nov 14 '22 at 08:18

score 8 · Answer 1 · edited May 23 '17 at 12:30

The first example is wrong because the assert expression will be removed when NDEBUG is defined, so s.erase(e) won't be called at all.

The argument of assert should NEVER have side-effects.

The second approach is better, though the warning might indeed be annoying, but there are ways to silence the warning.

Alternatively you could come up with your own assert statement that always executes the code.

#ifdef NDEBUG
#define assert_always_execute(x) (x)
#else
#define assert_always_execute(x) assert(x)
#endif

score -1 · Accepted Answer · answered Feb 02 '14 at 06:12

-1

I wrote my own like luiscubal's suggestion except instead of ugly #define's I made a short inline method:

inline void assert_always_execute(bool x) {
    assert(x);
}

answered Feb 02 '14 at 06:12

dspyz

1

...which still complains about `unused parameter 'x'` when compiled with `NDEBUG`, and thus solves the problem, how? – DevSolar May 28 '15 at 07:16
and also, the very obvious drawback is now you get told only that `b` failed, instead of whatever condition you were actually asserting originally... – underscore_d Nov 14 '22 at 08:20

2 Answers2