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POunordered_map of vectors resetting vectors
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  1. POunordered_map of vectors resetting vectors
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    copied!<p>I am trying to build a class to handle key callbacks.</p> <p>To do this I have a map defined as so:</p> <pre><code>class Keyboard { public: void registerCallback(int key, callback_fn func, bool repeat = false); void onKeyEvent(int key, int state); private: typedef std::function&lt;void (int)&gt; callback_fn; struct Callback { Callback(callback_fn f, bool r) : func(f), repeat(r), last_state(-1) {} callback_fn func; bool repeat; int last_state; }; std::unordered_map&lt;int, std::vector&lt;Callback&gt;&gt; callbacks; }; </code></pre> <p>I then register callbacks like so:</p> <pre><code>void Keyboard::registerCallback(int key, callback_fn func, bool repeat) { // My understanding is that if there is nothing mapped to the key // it will create a new vector. Otherwise it will return the mapped // object. I did try checking if anything already exists at the key // and if not creating a new vector but it yielded the same results. callbacks[key].push_back({ func, repeat }); } </code></pre> <p>However I am having an issue where the mapped vector appears to lose all of it's elements.</p> <p>When I register a callback the vector at the given key increases in size but when I try to iterate over the vector in another method, it has no elements.</p> <p>Below is how my method for iterating over the vector.</p> <pre><code>void Keyboard::onKeyEvent(int key, int state) { for(auto&amp; callback : callbacks[key]) { if(callback.repeat || callback.last_state != state) { callback.func(state); } } } </code></pre> <p>Note if I add <code>std::cout &lt;&lt; callbacks[key].size() &lt;&lt; std::endl;</code> to the top of the function it prints <code>0</code>.</p> <p>If it matters here is an example of how I register a callback.</p> <pre><code>keyboard.registerCallback('w', [](int state) { std::cout &lt;&lt; "w " &lt;&lt; (state == GLFW_PRESS ? "pressed" : "released") &lt;&lt; std::endl; }, true); </code></pre> <p>I suspect my problem stems from differences between Java's maps, which I am more used to, and C++'s maps</p>
 

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