Shifting back <vector> items...

This is a discussion on Shifting back <vector> items... within the C++ Programming forums, part of the General Programming Boards category; Hello, I have a vector filled with a structure. Now, I do pMyVec.erase (pMyVec.begin() + 2) for example. Now.. my ...

  1. #1
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    Angry Shifting back <vector> items...

    Hello,
    I have a vector filled with a structure. Now, I do
    pMyVec.erase (pMyVec.begin() + 2) for example.

    Now.. my question. Will pMyVec[2] still work for the next item? or do I have to shift back the items following the iterator I erased?
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  2. #2
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    I think when you erase elements from vectors the elements after it are moved up.

  3. #3
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    The index is still valid MyVec[2] is a copy of MyVec[3], MyVec[3] now contains MyVec[4] and so on. If you are going to be doing this a lot and you need to preserve order your best bet is with a list. If the order doesn't matter copy the last element to the element you want to delete and delete the last element.

    Code:
    MyVec[2] = MyVec.back();
    MyVec.pop_back();
    Note that sometimes you get even better performance by swapping the element with the last element as often a swap can be implemented in terms of swapping pointers rather than a deep copy

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