Sorting a vector of objects

I'm implementing kruskal's algorithm and ran into some troubles compiling. I need to sort a vector of objects by value. Here is my code and the error I'm getting.

Code:

---

//These are the two functions in graph.cpp (there are more but are unrelated)
#include <vector>
#include <algorithm>
#include <iostream>

using namespace std;

#include "graph.h"
#include "edge.h"

using std::vector;

void graph::sort_edgesArray()
{
  sort (edgesArray.begin(), edgesArray.end(), graph::cmp_val);
}

bool graph::cmp_val (edge& a, edge& B)
{
  return (a.val < b.val);
}

---

Code:

---

//This is the header file graph.h
#ifndef GRAPH_H
#define GRAPH_H

#include <vector>
#include "edge.h"

using std::vector;

class graph
{
 public:
 
  int nEdges;
  int nVerts;
  vector<edge> edgesArray;            //array that holds edges
  //might need a vertices vector

  graph() :
    nEdges(0),
    nVerts(0)
    {}

  void addVert(int vert);
   
  void addEdge(int start, int end, int value);

  int get_edges();

  int get_verts();

  void sort_edgesArray();

  bool cmp_val(edge& a, edge& b);
};

#endif

---

Code:

---

//This is the edge.h header file where graph.cpp is calling from to construct the vector.
#ifndef EDGE_H
#define EDGE_H

//Edges class in the graph
class edge
{
 public:
 
  int node1;
  int node2;
  int val;

  //constructor
 edge(int start, int end, int value) :
    node1(start),
    node2(end),
    val(value)
    {}
   
};  //end class edge

#endif

---

Code:

---

//This is the error I'm getting.
graph.cpp: In member function ‘void graph::sort_edgesArray()’:
graph.cpp:39:33: error: no matching function for call to ‘sort(std::vector<edge>::iterator&, std::vector<edge>::iterator&, <unresolved overloaded function type>)’
/usr/include/c++/4.5/bits/stl_algo.h:5236:18: note: candidate is: void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = __gnu_cxx::__normal_iterator<edge*, std::vector<edge> >, _Compare = bool (graph::*)(edge&, edge&)]

---

Quote:

---

Originally Posted by edishuman

I'm implementing kruskal's algorithm and ran into some troubles compiling. I need to sort a vector of objects by value. Here is my code and the error I'm getting.

---

See http://www.parashift.com/c++-faq-lit....html#faq-33.3.
You either need to make the function cmp_val a static member function or (better) make it a global function (possibly in an anonymous namespace). You can also overload operator < for the edge class, such that you can omit the third argument to std::sort.

Some other notes:
- Don't put a using declaration in the global scope of a header file. This effectively makes namespaces useless.
- You don't need to store the number of edges, since it is already given by edgesArray.size().
- Don't make data members of a class public. Make them private and define public member functions that do whatever the class needs to do. If you need to, provide accessor functions to a member variable.

bool graph::cmp_val (edge& a, edge& B)

why pass by reference? Should be value or const ref.

Another idea would be to just implement your operator<, if it makes sense.