typedef std::multimap<std::string,float> StringFloatMap;
StringFloatMap coll;
StringFloatMap::iterator pos;
...
for (pos = coll.begin(); pos != coll.end(); ) {
    if (pos->second == value) {
        pos = coll.erase(pos);        // Õîðîøî áû, íî...
    }                                 // ïðîèñõîäèò ÎØÈÁÊÀ ÊÎÌÏÈËßÖÈÈ!
    else {
        ++pos;
    }
}