Question

My STL is a bit rusty, so forgive me for asking a possibly trivial question. Consider the following piece of code:

map<int,int> m;
...
for (auto itr = m.begin(); itr != m.end(); ++itr) {
    if (itr->second == 0) {
        m.erase(itr);
    }
}

The question is: Is it safe to erase elements while looping over the map?

Answer 1

I think that you shouldn’t use removed iterator at all – in case of lists this causes serious problems, shouldn’t be different for maps.

EDIT by Matthieu M: this code is well-formed in C++0x and allowed as an extension by MSVC.

map<int,int> m;
...
auto itr = m.begin();
while (itr != m.end())
{
    if (itr->second == 0) {
        itr = m.erase(itr);
    }
    else 
    {
        itr++;
    }
}