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copied!<blockquote> <p>Is there a way (e.g. some coding convention I could follow from now on) I could have prevented this from hurting me?</p> </blockquote> <p>This may sound snarky, but: by reading the documentation.</p> <p>Since what you did is somewhat <em>expected</em> behaviour of the map, there’s not much you can do to guard against it.</p> <p>One thing you <em>can</em> heed in the future is the following. In your second step, you did something wrong:</p> <blockquote> <p>Check the return value and if NULL use insert to insert a new element in the map.</p> </blockquote> <p>This does <strong>never</strong> work with C++ standard library functions (other than C compatibility functions and <code>new</code>): the standard library doesn’t deal in pointers, least of all null pointers, so checking against <code>NULL</code> (or <code>0</code> or <code>nullptr</code>) rarely makes sense. (Apart from that, it wouldn’t make sense for a map’s <code>operator []</code> to return a pointer in the first place. It <em>obvoiusly</em> returns the <em>element type</em> (or rather, a reference to it)).</p> <p>In fact, the standard library predominantly uses <em>iterators</em> so if at all, check for iterator validity by comparing against the <code>end()</code> of a container.</p> <p>Unfortunately, your code (checking against <code>NULL</code>) compiled since <code>NULL</code> is actually a macro that’s equal to <code>0</code> in C++ so you can compare it against an integer.</p> <p>C++11 gets safer by introducing the <code>nullptr</code> keyword which has a distinct type, so comparing it with an integer wouldn’t compile. So this is a useful coding convention: never use <code>NULL</code>, and instead compile with C++11 support enabled and use <code>nullptr</code>.</p>

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