Iterating over std::map<X,std::vector<Y> > and sorting the vectors

Question

When iterating over std::map<X,std::vector<Y> >, may I sort the vectors, or might that invalidate the iterator?

In other words, is the following code okay?

typedef std::map<int, std::vector<int> > Map;
Map m;
for (Map::iterator it = m.begin(); it != m.end(); ++it) {
  std::sort(it->second.begin(), it->second.end());
}

Answer 1

Your code is okay. Iterators from a map are only invalidated when you remove elements from the map. Modifying an element of an STL container never invalidates that container's iterators, only operations on the container itself, like removing or sometimes adding elements.

Answer 2

Your code is perfectly fine. As a matter of fact, you shouldn't have any doubt as you are neither inserting nor removing elements from the map : the structure of the map is unchanged, you are only affecting the values stored.