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POWhat happens if you increment an iterator that is equal to the end iterator of an STL container
 

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  1. POWhat happens if you increment an iterator that is equal to the end iterator of an STL container
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    <p>What if I increment an iterator by 2 when it points onto the last element of a vector? In <a href="https://stackoverflow.com/questions/1057529/how-to-increment-an-iterator-by-2">this question</a> asking how to adjust the iterator to an STL container by 2 elements two different approaches are offered:</p> <ul> <li>either use a form of arithmetic operator - +=2 or ++ twice</li> <li>or use std::advance()</li> </ul> <p>I've tested both of them with VC++ 7 for the edge case when the iterator points onto the last element of the STL container or beyond:</p> <pre><code>vector&lt;int&gt; vec; vec.push_back( 1 ); vec.push_back( 2 ); vector&lt;int&gt;::iterator it = vec.begin(); advance( it, 2 ); bool isAtEnd = it == vec.end(); // true it++; // or advance( it, 1 ); - doesn't matter isAtEnd = it == vec.end(); //false it = vec.begin(); advance( it, 3 ); isAtEnd = it == vec.end(); // false </code></pre> <p>I've seen may times an advise to compare against vector::end() when traversing the vector and other containers:</p> <pre><code>for( vector&lt;int&gt;::iterator it = vec.begin(); it != vec.end(); it++ ) { //manipulate the element through the iterator here } </code></pre> <p>Obviously if the iterator is advanced past the last element inside the loop the comparison in the for-loop statement will evaluate to false and the loop will happily continue into undefined behaviour.</p> <p>Do I get it right that if I ever use advance() or any kind of increment operation on an iterator and make it point past the container's end I will be unable to detect this situation? If so, what is the best practice - not to use such advancements?</p>
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