title: Using STL Data Structures
body: <p>Please help:</p>
  
  <p>g++ (GCC) 3.4.4</p>
  
  <p>I have two '.hpp' files: 'UnionFind.hpp' and "Graph.hpp". The content of the files is as follows:</p>
  
  <pre><code>#ifndef UNIONFIND_HPP
  #define UNIONFIND_HPP
  
  #include &lt;vector&gt;
  
  using std::vector;
  
  class UnionFind
  {
     public:
        UnionFind(uint32_t size);
        ~UnionFind();
        int find(uint32_t target);
        void join(uint32_t a, uint32_t b);
        void print();
     private:
        uint32_t size;
        uint32_t* index;
        vector&lt;uint32_t&gt;** sets;
  };
  
  #endif
  </code></pre>
  
  <p>And the other:</p>
  
  <pre><code>#ifndef GRAPH_HPP
  #define GRAPH_HPP
  
  #include &lt;set&gt;
  
  using std::set;
  
  class Graph
  {
     public:
        Graph(uint32_t width, uint32_t length, uint32_t startN, uint32_t startP, uint32_t endN, uint32_t endP);
        ~Graph();
        int cost(uint32_t a, uint32_t b);
        void set(uint32_t a, uint32_t b, uint32_t cost);
        void print();
        bool inPath(uint32_t node);
     private:
        int32_t** adjList;
        uint32_t startN;
        uint32_t startP;
        uint32_t endN;
        uint32_t endP;
        set&lt;uint32_t&gt;* path;
        const uint32_t width;
        const uint32_t length;
        const uint32_t size;
        const uint32_t listWidth;
  };
  
  #endif
  </code></pre>
  
  <p>For some reason I get the following errors:</p>
  
  <pre><code>./Graph.hpp:23: error: ISO C++ forbids declaration of `set' with no type
  ./Graph.hpp:23: error: expected `;' before '&lt;' token
  </code></pre>
  
  <p>I had previously run into the problem of not including 'using std::vector' in the 'UnionFind.hpp', but adding 'using std::set' to 'Graph.hpp' does not fix the problem. Also,
  I've tried 'using std::set&lt; uint32_t >', but this gives the following errors:</p>
  
  <pre><code>./Graph.hpp:6: error: a template-id may not appear in a using-declaration
  ./Graph.hpp:23: error: ISO C++ forbids declaration of `set' with no type
  ./Graph.hpp:23: error: expected `;' before '&lt;' token
  </code></pre>