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POManual control of iterator when erasing (and deleting) is necessary
 

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    <p>In a particle system, once particles become old enough, they need to die. Since they are stored in an <code>std::vector</code> the approach that works rather well in XCode is:</p> <pre><code>for(std::vector&lt;Particle*&gt;::reverse_iterator iter = particles.rbegin(); iter != particles.rend(); ++iter) { (*iter)-&gt;update(); if ( (*iter)-&gt;isDead() ) { delete (*iter); particles.erase( --iter.base() ); } } </code></pre> <p>After booting into Windows, and compiling in Visual Studio 2010, I found that it doesn't work: see <a href="https://stackoverflow.com/questions/404258/how-do-i-erase-a-reverse-iterator-from-an-stl-data-structure">here</a>. As the answer itself states, this does not work for associative containers. What I find most frustrating here is that <code>std::reverse_iterator</code> and <code>std::iterator</code> behave differently:</p> <ul> <li><code>.erase</code> does not take a <code>reverse_iterator</code> and wants a real thing (e.g. see <a href="https://stackoverflow.com/questions/8621426/how-do-you-erase-and-continue-using-a-stdreverse-iterator">this</a>)</li> <li><code>rev_it.base()</code> call needs to be decremented in the erase call </li> <li>after erasing, I need to convert the <code>std::iterator</code> to an <code>std::reverse_iterator</code></li> </ul> <p>I thought of using a forward <code>std::iterator</code> but iterating backwards, which <a href="https://stackoverflow.com/questions/1853358/use-a-regular-iterator-to-iterate-backwards-or-struggle-with-reverse-iterator">is a terrible idea</a> - but the very need for iterating backwards, really, is to ensure that the loop doesn't skip neighboring members of erased <code>particles</code>.</p> <p>What makes sense to me, though, is <em>not iterating if the <code>.erase()</code> call is made</em>:</p> <pre><code>for( std::vector&lt;Particle*&gt;::iterator iter = particles.begin(); iter != particles.end(); ) { (*iter)-&gt;update(); if ( (*iter)-&gt;isDead() ) { delete (*iter); iter = particles.erase(iter); } else { ++iter; } } </code></pre> <p>This compiles, works, and doesn't seem to be a problem. The question, though, is:</p> <p><strong>Am I overlooking something that renders this a particularly stupid idea?</strong></p> <p>(I'm sure that <code>iter</code> will point at the correct next value by taking advantage of the <code>.erase()</code> function's <code>return</code> value, and it seems more readable to me than <code>--iter.base()</code> call.)</p> <p>That parenthetical aside, a Russian saying that comes to mind is <em>"One who's been burned on hot milk blows on cold water."</em> </p>
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    1. COCan you afford two passes? One to delete and mark the deleted elements (set to NULL for example), another one to remove NULL elements from the vector?
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    2. COCan't you just use `std::remove_if`?
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    3. CO@juanchopanza Certainly, but I will still need to iterate through the `vector` without skipping any members, otherwise later on I'll be calling `draw()` on NULL elements!
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