Question

I almost never put a ++ or — anywhere except on its own line. I know they can lead to undefined behavior and can be hell for debugging. But for verbosity purposes, I’m tempted. Is this valid code?

map<int, int> dict;

...

int key = ...;
if (dict.lower_bound(key) != dict.begin()) {
  int prevval = (--dict.lower_bound(key))->second;
  ...
}

I’d like to just do

int prevval = (dict.lower_bound(key)-1)->second;

but bidirectional iterators don’t have operator-() defined.

Thanks!

Answer 1

Yes, it’s perfectly valid and works as expected.

Undefined behavior when using these operators usually come from modifying a variable multiple times between sequence points, which is not your case.