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POShould one really set pointers to `NULL` after freeing them?
 

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  1. POShould one really set pointers to `NULL` after freeing them?
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    <p>There seem to be two arguments why one should set a pointer to <code>NULL</code> after freeing them.</p> <h2><a href="https://stackoverflow.com/questions/1879168/why-set-a-pointer-to-null-after-calling-free-in-c/1879173#1879173">Avoid crashing when double-freeing pointers.</a></h2> <p><em>Short: Calling <code>free()</code> a second time, by accident, doesn't crash when it's set to <code>NULL</code>.</em></p> <ul> <li><p>Almost always this masks a logical bug because there is no reason to call <code>free()</code> a second time. It's safer to let the application crash and be able to fix it.</p></li> <li><p>It's not guaranteed to crash because sometimes new memory is allocated at the same address.</p></li> <li><p>Double free occurs mostly when there are two pointers pointing to the same address.</p></li> </ul> <p>Logical errors can lead to data corruption too.</p> <h2><a href="https://stackoverflow.com/questions/1025589/setting-variable-to-null-after-free/1025604#1025604">Avoid reusing freed pointers</a></h2> <p><em>Short: Accessing freed pointers can cause data corruption if <code>malloc()</code> allocates memory in the same spot unless the freed pointer is set to <code>NULL</code></em></p> <ul> <li><p>There's no guarantee that the program crashes when accessing the <code>NULL</code> pointer, if the offset is big enough (<code>someStruct-&gt;lastMember</code>, <code>theArray[someBigNumber]</code>). Instead of crashing there will be data corruption.</p></li> <li><p>Setting the pointer to <code>NULL</code> cannot solve the problem of having a different pointer with the same pointer value.</p></li> </ul> <h2>The questions</h2> <p>Here's <a href="https://stackoverflow.com/questions/1879168/why-set-a-pointer-to-null-after-calling-free-in-c/1879469#1879469">a post against blindly setting a pointer to <code>NULL</code> after freeing</a>.</p> <ul> <li>Which one is harder to debug?</li> <li>Is there a possibility to catch both?</li> <li>How likely is it, that such bugs lead to data corruption instead of crashing?</li> </ul> <p><em>Feel free to expand this question.</em></p>
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    1. USGeorg Schölly
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    1. CODupe of http://stackoverflow.com/questions/1879168/why-set-a-pointer-to-null-after-calling-free-in-c among many others.
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    2. COThe x-ref to [SO 1879168](http://stackoverflow.com/questions/1879168/why-set-a-pointer-to-null-after-calling-free-in-c/1879469#1879469) in the article is broken for me today — the SO server throws up a 404 page. Can you track down and update the x-ref? Or provide one or more alternatives? There seem to be plenty to choose from.
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      1. USJonathan Leffler
 

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