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POSTL Sort on nested Classes
 

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    <p>I have a graph class that has a vector of nodes. In each node, there is a vertex and a STL list of edges. Essentially it's an adjacency list.</p> <p>For my assignment, I am trying to display the vertices with the most edges. I figured I would sort the graph's vector of nodes by edge size and print the top N vertices.</p> <p>So I am trying to figure out STL sort, but I'm having difficulties.</p> <p>I have </p> <pre><code> std::sort(path.begin(), path.end()); </code></pre> <p>Where path is the vector of nodes (node = vertex value and list of edges)</p> <p>In my node class, I have </p> <pre><code>bool operator&lt;(const Node&lt;T&gt;&amp; rhs){ return size &lt; rhs.size; //size is how many edges the vertex has } </code></pre> <p>But it's giving me errors. How can I construct the <code>operator&lt;</code> function in my node class to work with STL sort?</p> <p>Here are the errors:</p> <pre><code>$ make g++ -c -g -std=c++0x graphBuilder.cpp In file included from /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/algorithm:63:0, from graph.h:6, from graphBuilder.cpp:2: /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/bits/stl_algo.h: In function '_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&amp;) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator&lt;Node&lt;std::basic_string&lt;char&gt; &gt;*, std::vector&lt;Node&lt;std::basic_string&lt;char&gt; &gt;, std::allocator&lt;Node&lt;std::basic_string&lt;char&gt; &gt; &gt; &gt; &gt;, _Tp = Node&lt;std::basic_string&lt;char&gt; &gt;]': /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/bits/stl_algo.h:2249:70: instantiated from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator&lt;Node&lt;std::basic_string&lt;char&gt; &gt;*, std::vector&lt;Node&lt;std::basic_string&lt;char&gt; &gt;, std::allocator&lt;Node&lt;std::basic_string&lt;char&gt; &gt; &gt; &gt; &gt;]' /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/bits/stl_algo.h:2280:54: instantiated from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator&lt;Node&lt;std::basic_string&lt;char&gt; &gt;*, std::vector&lt;Node&lt;std::basic_string&lt;char&gt; &gt;, std::allocator&lt;Node&lt;std::basic_string&lt;char&gt; &gt; &gt; &gt; &gt;, _Size = int]' /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/bits/stl_algo.h:5212:4: instantiated from 'void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator&lt;Node&lt;std::basic_string&lt;char&gt; &gt;*, std::vector&lt;Node&lt;std::basic_string&lt;char&gt; &gt;, std::allocator&lt;Node&lt;std::basic_string&lt;char&gt; &gt; &gt; &gt; &gt;]' graph.h:32:13: instantiated from 'void Graph&lt;T&gt;::topN(int) [with T = std::basic_string&lt;char&gt;]' graphBuilder.cpp:10:17: instantiated from here /usr/lib/gcc/i486-slackware-linux/4.5.2/../../../../include/c++/4.5.2/bits/stl_algo.h:2211:4: error: passing 'const Node&lt;std::basic_string&lt;char&gt; &gt;' as 'this' argument of 'bool Node&lt;T&gt;::operator&lt;(const Node&lt;T&gt;&amp;) [with T = std::basic_string&lt;char&gt;]' discards qualifiers make: *** [graphBuilder.o] Error 1 </code></pre>
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    1. COWhat errors? That would help to diagnose.
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    2. COIts considered a good practice to include error messages in your question
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    3. COAdded error messages, thanks
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