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POOverloading Iterator: C++ Semantics Question
 

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  1. POOverloading Iterator: C++ Semantics Question
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    <p>Please note this code was not written by me. Otherwise I would not be asking this question. Full credit goes to <a href="https://codereview.stackexchange.com/users/489/jerry-coffin">Jerry Coffin</a>. Anyways the code generates a sequence of numbers by overloading std::iterator&lt; >.</p> <p>I will first post the code, then I will give my interpretation of what I am seeing. If an expert C++ member could correct me if I am wrong I would greatly appreciate it.</p> <p><strong>Code</strong></p> <pre><code>static const int N = 10; template &lt;class T&gt; class sequence : public std::iterator&lt;std::forward_iterator_tag, T&gt; { private: T val; public: sequence(T init) : val(init) { } T operator *( ) { return val; } sequence &amp;operator++( ) { ++val; return *this; } bool operator != ( const sequence &amp;other ) { return val != other.val; } }; void foo( ) { typedef std::vector&lt;int&gt; graph; graph id1( gen_seq(0), gen_seq( N ) ); display( id1 ); /* Not declared */ } /* displays: 0 1 2 3 4 5 6 7 8 9 */ </code></pre> <p>So when looking at this I see that you create a class which contains a value. Now we pass two of those to vector's constructor, which can takes two iterators. Now each time vector's constructor uses the ++ operator on the "sequence" it increments the value inside of the iterator. Technically, you could write:</p> <pre><code>graph id1( gen_seq( 0 ), gen_seq( 0 ) ); </code></pre> <p>and this would generate the same sequence correct? Or is it the != operator that checks to make sure 0 has not gone to N. Any input on this would help greatly. I just finished reading Stroustrup's C++ Programming Language 3rd edition where he touched upon iterators, however inheriting from them was not a big topic and something I am not fully understanding. Kind of whish I would have done all his exercises, because I remember him asking to overload an iterator a few times.</p>
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    1. USCommunity
    1. USMatthew Hoggan
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    1. COThis isn't overloading, it's just inheritance.
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      1. POOverloading Iterator: C++ Semantics Question
      1. USSeth Carnegie
    2. COSorry used wrong term. I will edit my post
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      1. POOverloading Iterator: C++ Semantics Question
      1. USMatthew Hoggan
    3. COFor completeness sake, note also that a forward iterator must provide the following operations as well: default construction, postfix `++`, and equality (`==`). All three of those can easily be defined in terms of the operators that you've already defined.
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      1. POOverloading Iterator: C++ Semantics Question
      1. USJames McNellis
 

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