Question

I have a multimap with Note objects from which I want to remove only one object. There can be several Note objects with the same key. The problem is that right now there’s also objects being removed that aren’t within the key range I specify:

long key = note.measureNumber * 1000000 + note.startTime; // = 2000001
multimap<long, Note>::iterator it;
for (it = noteList.lower_bound(key); it != noteList.end() && it->first < (key + 1); it++) {
    if(it->second.frequency == note.frequency){
        noteList.erase(it);
    }
}

When I run this code with key 2000001 the object I’m able to erase the right object, but another object with key 1000017 gets erased as well. Both objects have the same frequency though.

Any idea’s what is wrong with my for loop?

EDIT: To be clear, I only want to check for objects with one specific key (in this case 2000001) there’s no need for the iterator to look at objects with different keys than that one.

Answer 1

Once you erase an iterator it becomes invalid. If you wish to erase from a map while you iterate through it, your code needs to change. Try this:

multimap<long, Note>::iterator it;
for (it = noteList.lower_bound(key); it != noteList.end() && it->first < (key + 1);) {
    if(it->second.frequency == note.frequency){
        noteList.erase(it++);
    }
    else
    {
        ++it;
    }
}