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POC++: insert tuple in multiset with std::function, and keeping an order
 

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  1. POC++: insert tuple in multiset with std::function, and keeping an order
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    <p>Quite simply, what's wrong with this piece of code?</p> <pre><code> typedef std::function&lt;double()&gt; Event; typedef std::tuple &lt;double, std::function&lt;double()&gt;&gt; Event_handle; std::multiset &lt; Event_handle &gt; event_multiset; std::vector &lt; Event_handle &gt; event_vector; void add_event_handler(double time, Event func_object) { // multiset version gives an error // event_multiset.insert (std::make_tuple(time, func_object)); // vector is ok event_vector.push_back(std::make_tuple(time, func_object)); } </code></pre> <p>compiled using <code>g++ 4.7.2</code> - with command simply <code>g++ -std=c++11 main.cpp</code></p> <p><strong>Why I want to do this?</strong></p> <p>The program is run in real time and the <code>add_even_handler</code> function includes a value of type <code>double</code> called <code>time</code> (note that <code>time</code> variable here has nothing to do with clock or actual time, it is just an increasing object of type double). Therefore when a user add some event it will be called at a certain time.</p> <p>A multiset container under the standard would collate the objects in some order (usually, if not always, <code>std::less&lt;T&gt;</code>). Then looping over the container, I could call the <code>Event</code> upon increasing changes of variable <code>double time</code>.</p> <p><strong>What is the problem?</strong></p> <p>As KyleC has pointed out (see his answer), <code>std::function&lt;&gt;</code> is not understood by the compiler in what process to order</p> <p><strong>How I've overcome the problem</strong></p> <p>You learn something new everyday. The above code was a result of overthinking the problem by initially mixing <code>std::multiset</code> and <code>std::tuple</code>. <code>std::map&lt;T,S&gt;</code> or <code>std::multimap&lt;T,S&gt;</code> is also sorted by an associated <code>key</code> which in this case is of type <code>double</code>, which by default by the standard is again <code>std::less&lt;T&gt;</code>. So instead of the above, I've done something similar to the following</p> <pre><code>std::multimap &lt;double, event&gt; event_map; void add_event_handler(double time, Event func_object) { // multimap is ok event_map.insert(std::make_pair(time,func_object)); } </code></pre> <p>This is just written here in the event it may help people, albeit obvious but nonetheless.</p>
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    1. COcan you post the relevant portion of the error?
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      1. USKyle C
    2. CO@KyleC quick question, how do you output compiler errors to text file in g++?
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      1. USwoosah
 

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