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copied!<p>As andre said, to avoiding overloading operators on your struct you can use the following map:</p> <p><code>std::map<std::pair<int, int>, int> a_map;</code></p> <p><strong>Insertion:</strong></p> <p>Insert into it with <code>a_map.insert(std::pair<std::pair<int,int>, int>(std::pair<int,int>(x, y), z));</code></p> <p>or</p> <p><code>std::pair<int, int> index(x, y); a_map[index] = z;</code></p> <p>or (neatest version, borrowed from andre's answer)</p> <p><code>a_map[make_pair(x, y)] = z;</code></p> <p><strong>Access:</strong></p> <p>If you're only iterating through the elements and don't particularly care about accessing values by their index very often this method is fine. If you <em>do</em> want to do that then you can access them like so:</p> <p><code>std::pair<int, int> index(x, y); int z = a_map[index];</code></p> <p>or (neatest version)</p> <p><code>int z = a_map[make_pair(x, y)];</code></p> <p>You could also use <code>find()</code> but once again, you'll need to construct a <code>pair</code> for it (<a href="http://www.cplusplus.com/reference/map/map/find/" rel="nofollow">http://www.cplusplus.com/reference/map/map/find/</a>).</p> <p>You can use the <code>make_pair()</code> function from <code><utility></code> (<a href="http://www.cplusplus.com/reference/utility/make_pair/" rel="nofollow">http://www.cplusplus.com/reference/utility/make_pair/</a>) to make constructing the pairs a bit easier but if you don't want to use a map with pairs as the indexes then you might want to revert to the original plan and use an <code>std::map<pos, int></code> instead. </p> <p><strong>Alternative map:</strong></p> <p>If you decide to use <code>std::map<pos, int></code> just remember to overload <code>operator<</code> on <code>pos</code> to allow your <code>map</code> to sort its keys (since you aren't actually making any use of the sorting feature, you can return the comparison of either <code>pos::x</code> or <code>pos::y</code> arbitrarily).</p> <p><strong>Unordered map:</strong></p> <p>If you want to avoid the need to overload the operator and the sorting entirely, you can use the new C++11 <code>unordered_map</code> which is a more efficient container for insertions and deletions anyway. Since you're only using the uniqueness and iterator properties of <code>map</code>, it would be worth considering using <code>unordered_map</code> if you can (they have very similar interfaces and I've used them in place of <code>map</code> just by changing the type of my variable before!) </p>

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