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PODynamic memory and constructor exceptions
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copied!<p>Early today I discovered function try-catch blocks (from <a href="https://stackoverflow.com/questions/75538/hidden-features-of-c/152659#152659">here</a> in fact) and then went on a bit of a research spree - apparently they're main use is it catch exceptions throw in by a constructor initialiser list.</p> <p>Anyway, this sent me thinking about failing constructors and I've got to a stage where I just need a little clarification. This is all just me trying to learn more about the language, so I don't have a <em>practical</em> example, but here goes...</p> <hr> <p>Given this example code:</p> <pre><code>class A { private: B b C *c; //classes B, C & D omitted for brevity as not really relevant D d; public A(int x, int y, int z) }; A::A(int x, int y, int z) try : b( x ) , c( new C(y) ) , d( z ) { //omitted } catch(...) { //omitted } </code></pre> <p>What happens in these cases:</p> <ol> <li>The initialisation of <code>b</code> throws an exception.</li> <li>The initialisation of <code>c</code> throws an exception.</li> <li>The initialisation of <code>d</code> throws an exception.</li> </ol> <p>Specifically, I want to know at least:</p> <ul> <li>what will/may cause a memory leak from <code>new C(y)</code>. <em>I'm thinking only 3? (see <a href="https://stackoverflow.com/questions/1674980/who-deletes-the-memory-allocated-during-a-new-operation-which-has-exception-in">here</a>)</em></li> <li>could you just <code>delete b</code> in the catch? <em>Is dangerous in cases 1 and 2?</em></li> </ul> <p>Obviously, I guess the safest thing to do is to make <code>c</code> a smart pointer. But disregarding that option for the moment, what's the best course of action? </p> <p>Is it safe to set <code>c</code> to <code>NULL</code> in the initialiser, and then place the call to <code>new</code> in the constructor body? </p> <p>That would then mean a <code>delete c</code> must be placed in the catch in case something else throws in the constructor body? Are there safety issues doing that (ie, if it's the <code>c = new C(y);</code> itself that throws)?</p>

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