Iterator newbie question

This is a discussion on Iterator newbie question within the C++ Programming forums, part of the General Programming Boards category; Hi everyone! How can I index a list with an integer? I canīt add integers to iterators Thanks any help!...

  1. #1
    Disturbed Boy gustavosserra's Avatar
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    Iterator newbie question

    Hi everyone!
    How can I index a list with an integer? I canīt add integers to iterators
    Thanks any help!
    Nothing more to tell about me...
    Happy day =)

  2. #2
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    A linked list?
    Linked lists generally don't support random accessing, i.e. indexing, as it's horribly slow. Generally iterators override the increment and de-increment operators (++, --), in order to walk through the list.

    If you really needed to, you could overload the arithmetic operators (+, -), with code like this:
    Code:
    iterator List::operator+(iterator pos, int index)
    {
    	for(size_t count = 0; count < index; count++)
    	{
    		pos++
    	}
    	return pos;
    }
    With that you could write the operator[] function fairly easily by starting with the beginning element of the list and adding the index. However I don't remember the syntax for that particular operator, so I'll leave that to you or someone else to look up.
    Last edited by AH_Tze; 05-26-2004 at 05:02 PM.

  3. #3
    Carnivore ('-'v) Hunter2's Avatar
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    Why not use a vector instead of a list?
    Just Google It. √

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  4. #4
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    I'm going to feel really silly if that was the answer he was looking for. I've been working on implementing a linked-list for the last month in my data structs class, so I just assumed people randomly rewrite basic containers for no reason.
    /me heads off for a very long nap

  5. #5
    Carnivore ('-'v) Hunter2's Avatar
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    Well, anyways if you do need some list-exclusive functionality, you can do the operator+ overloading if you're indexing only rarely, or you can use a vector and use a STL copy algorithm to transfer the vector to a list, use the list functionality and convert back to vector, if the list functionality is rarely needed (by rarely I mean 'once every half hour or more'). Of course, most of the time option (a) will be the better choice, especially if you have a lot of elements in the container, but if you don't need that list stuff, you might as well use a vector.

    Actually, the thought just occurred to me that you might want to use a std::deque, since it's got indexing and still has most of the std::list stuff that you might want.
    Just Google It. √

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  6. #6
    Disturbed Boy gustavosserra's Avatar
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    Thanks for the help!
    I was thinking in something like:
    Code:
    int returnElement(list<int>& l, int index){
       return *(l.begin() + index);
    }
    But I'll use vectors.
    Nothing more to tell about me...
    Happy day =)

  7. #7
    Carnivore ('-'v) Hunter2's Avatar
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    >>I'm going to feel really silly if that was the answer he was looking for.
    Has it started yet?
    Just Google It. √

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