Vector erase iterator

Question

I have this code   int main         vector lt int gt  res      res push back 1       vector lt int gt   iterator it   res begin        for    it    res end    it                  it   res erase it             if it    res end                return 0             A random access iterator pointing to the new location of the element that followed the last element erased by the function call  which is the vector end if the operation erased the last element in the sequence    This code crashes  but if I use the if it    res end    portion and then return  it works  How come  Does the for loop cache the res end   so the not equal operator fails

User · Answer

Do not erase and then increment the iterator  No need to increment  if your vector has an odd  or even  I don t know  number of elements you will miss the end of the vector

User · Answer

Because the method erase in vector return the next iterator of the passed iterator   I will give example of how to remove element in vector when iterating   void test del vector        std  vector lt int gt  vecInt 0  1  2  3  4  5          method 1     for auto it   vecInt begin   it    vecInt end              if  it   2     remove all the odds             it   vecInt erase it      note it will   next it  after erase           else                it                          output all the remaining elements     for auto const amp  it vecInt std  cout lt  lt it      std  cout lt  lt std  endl          recreate vecInt  and use method 2     vecInt    0  1  2  3  4  5         method 2     for auto it std  begin vecInt  it  std  end vecInt             if   it   2               it   vecInt erase it            else                it                          output all the remaining elements     for auto const amp  it vecInt std  cout lt  lt it      std  cout lt  lt std  endl          recreate vecInt  and use method 3     vecInt    0  1  2  3  4  5         method 3     vecInt erase std  remove if vecInt begin    vecInt end                        const int a  return a   2                      vecInt end             output all the remaining elements     for auto const amp  it vecInt std  cout lt  lt it      std  cout lt  lt std  endl       output aw below   024 024 024   A more generate method   template lt class Container  class F gt  void erase where Container amp  c  F amp  amp  f        c erase std  remove if c begin    c end   std  forward lt F gt  f                c end        void test del vector        std  vector lt int gt  vecInt 0  1  2  3  4  5         method 4     auto is odd      int x  return x   2        erase where vecInt  is odd           output all the remaining elements     for auto const amp  it vecInt std  cout lt  lt it      std  cout lt  lt std  endl

User · Answer

for    it    res end           it   res erase it       or  more general   for    it    res end           if  smth          it   res erase it       else           it

User · Answer

As a modification to crazylammer s answer  I often use   your vector type  iterator it  for  it   res start    it    res end           your vector type  iterator curr   it        if  something          res erase curr       The advantage of this is that you don t have to worry about forgetting to increment your iterator  making it less bug prone when you have complex logic  Inside the loop  curr will never be equal to res end    and it will be at the next element regardless of if you erase it from your vector

User · Answer

The it   instruction is done at the end of the block  So if your are erasing the last element  then you try to increment the iterator that is pointing to an empty collection

User · Answer

res erase it  always returns the next valid iterator  if you erase the last element it will point to  end    At the end of the loop   it is always called  so you increment  end   which is not allowed    Simply checking for  end   still leaves a bug though  as you always skip an element on every iteration  it gets  incremented  by the return from  erase    and then again by the loop   You probably want something like    while  it    res end              it   res erase it            to erase each element   for completeness  I assume this is a simplified example  if you simply want every element gone without having to perform an operation on it  e g  delete  you should simply call res clear     When you only conditionally erase elements  you probably want something like  for     it    res end          if  condition        it   res erase it       else         it

User · Answer

The following also seems to work     for  vector lt int gt   iterator it   res begin    it    res end    it        res erase it--       Not sure if there s any flaw in this

User · Answer

Something that you can do with modern C   is using  std  remove if  and lambda expression   This code will remove  3  of the vector  vector lt int gt  vec  1 2 3 4 5 6    vec erase std  remove if begin vec  end vec     int elem  return  elem    3      end vec

User · Answer

if allPlayers empty      false        for int i   allPlayers size   - 1  i  gt   0  i--                if allPlayers at i  getpMoney    lt   0               allPlayers erase allPlayers at i              This works for me  And Don t need to think about indexes have already erased

User · Answer

You increment it past the end of the  empty  container in the for loop s loop expression

[c++] Vector erase iterator

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