How to call erase with a reverse iterator using a for loop
c++, c++11
Solution
After some use of this idiom, I think a modification to the loop in Jarod42's answer is in order to make things safer and maintain the typical `for(;;)` loop niceties:
for (auto it = testcont.rbegin(), nit = it; it != testcont.rend(); it = nit) {
nit = next(it);
// whatever... maybe a continue somewhere or maybe not
if (WE_WANT_TO_ERASE(it)) {
nit = decltype(it){ testcont.erase(std::next(it).base()) };
}
// whatever... maybe a continue somewhere or maybe not
}
Using the loop in the other answer is too dangerous. If one were to thoughtlessly add a `continue;` somewhere in the loop, without incrementing the iterator first, the result would be an infinite loop. Since, at first glace, this can look like a normal `for(;;)` loop, I believe that this is bound to happen sooner or later. Similarly, if there are branches in the loop, and if one of those branches neglects to increment the iterator, another bug is introduced. Finally, if you do an `erase()`, you need to be sure to `continue` before you increment the iterator or else you have yet another bug.
Using the modified loop above, the loop can be treated just like a normal `for(;;)` loop. The trick is to increment `nit` (the "next iterator") as the first line of the loop body. Then you don't have to worry. The only time you need to update `nit` is if you are doing an `erase()`. Everything else works as one would expect a for loop to work.
One final note: I originally asked the question with regard to maps, but this will work correctly for `vector`, `list`, etc, as well.
Problem
Regarding the answer provided here: How to call erase with a reverse iterator The following results in a segmentation fault (upon `++it`) when compiled in g++ 4.8.4 with -std=c++11. Am I misunderstanding the answer? ``` std::map<int,int> testmap; testmap[0] = 1; for(auto it=testmap.rbegin(); it!=testmap.rend(); ++it) { testmap.erase( std::next(it).base() ); } ```