vagetablechicken commented on issue #2697: Using a range for loop and erasing 
an item may cause mem error
URL: 
https://github.com/apache/incubator-doris/issues/2697#issuecomment-571913539
 
 
   Based on https://en.cppreference.com/w/cpp/language/range-for, I produce 
code equivalent to the following:
   ```
       for(auto beg=m.begin(), end=m.end(); beg !=end; ++beg){
           auto ita=(*beg).second.find(2);
           if(ita != (*beg).second.end()) (*beg).second.erase(2);
           if((*beg).second.empty()){
               m.erase((*beg).first);
           }
       }
   ```
   The valgrind report is the same like 'range for statement'.
   So I infer that using a range for loop and erasing an item can't avoid 
iterator invalidation. Although, I can't point out the root cause. Maybe the 
stl books have the answer.
   

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