Sorting a vector of structs....

This is a discussion on Sorting a vector of structs.... within the C++ Programming forums, part of the General Programming Boards category; When I try to compile the following code, insert Code: #include<iostream> #include<vector> #include<algorithm> using namespace std; class c { public: ...

  1. #1
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    Sorting a vector of structs....

    When I try to compile the following code,
    insert
    Code:
    #include<iostream>
    #include<vector>
    #include<algorithm>
    
    using namespace std;
    class c
    {
    public:
    struct match
    {
      int index;
      int count;
    
    }n;
    
    bool func(const match& a,const match& b)
    {
      return a.count<b.count;
    }
    
    void compare()
    {
      vector<match> chk;
      for(int i=5;i>=0;i++)
        {
          n.index=i;
          n.count=i;
          chk.push_back(n);
        }
    
      sort(chk.begin(),chk.end(),func);
      for(int i=0;i<chk.size();i++)
        {
          cout<<chk[i].index<<"   "<<chk[i].count<<endl;
        }
    
      //  return 0;
    
    
    }
    };
    int main()
    {
      c obj;
      obj.compare();
      return 0;
    }
    I get the following error....

    sample.cpp: In member function ‘void c::compare()’:
    sample.cpp:31: error: no matching function for call to ‘sort(__gnu_cxx::__normal_iterator<c::match*, std::vector<c::match, std::allocator<c::match> > >, __gnu_cxx::__normal_iterator<c::match*, std::vector<c::match, std::allocator<c::match> > >, <unresolved overloaded function type>)’
    /usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:2735: note: candidates are: void std::sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<c::match*, std::vector<c::match, std::allocator<c::match> > >, _Compare = bool (c::*)(const c::match&, const c::match&)]


    Aren't the iterators for a vector random access by default????Kindly help!!!!!

  2. #2
    The larch
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    func is a member function of c and as such needs to be called with an instance of c.

    Code:
    C c;
    c.func(match_a, match_b);
    As such it cannot be used as a predicate.

    However, since it doesn't require any knowledge of a c, you might make it a static class function.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
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  3. #3
    C++ Witch laserlight's Avatar
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    By the way, I suggest that you format your code properly, e.g.,
    Code:
    #include<iostream>
    #include<vector>
    #include<algorithm>
    
    using namespace std;
    class c
    {
    public:
        struct match
        {
            int index;
            int count;
        }n;
    
        bool func(const match& a,const match& b)
        {
            return a.count<b.count;
        }
    
        void compare()
        {
            vector<match> chk;
            for (int i=5;i>=0;i++)
            {
                n.index=i;
                n.count=i;
                chk.push_back(n);
            }
    
            sort(chk.begin(),chk.end(),func);
            for (int i=0;i<chk.size();i++)
            {
                cout<<chk[i].index<<"   "<<chk[i].count<<endl;
            }
    
            //  return 0;
        }
    };
    
    int main()
    {
        c obj;
        obj.compare();
        return 0;
    }
    This way it is easier to even see that func and compare are member functions of c.
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  4. #4
    Algorithm Dissector iMalc's Avatar
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    I'd think it would be more useful to put the comparison operator inside match and call it operator less-than. No need for the last parameter to sort unless you want to override the less-than operator of that class.
    Code:
    #include<iostream>
    #include<vector>
    #include<algorithm>
    
    using namespace std;
    class c
    {
    public:
        struct match
        {
            int index;
            int count;
            bool operator < (const match& a, const match& b)
            {
                return a.count < b.count;
            }
        } n;
    
        void compare()
        {
            vector<match> chk;
            for (int i=5; i>=0; i++)
            {
                n.index = i;
                n.count = i;
                chk.push_back(n);
            }
    
            sort(chk.begin(), chk.end());
            for (int i=0; i<chk.size(); i++)
            {
                cout << chk[i].index << "   " << chk[i].count << endl;
            }
        }
    };
    
    int main()
    {
        c obj;
        obj.compare();
        return 0;
    }
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  5. #5
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    Well ... I put the bool function and struct declaration outside class and it worked....

    Anyway the above sample code is just a part of my program... in the original code there are three integer variables in struct (percent, totalpercent & score being the three variables). I've sorted them using three bool functions.... I'd like to know if there is a more object oriented way of doin the same(like iMalc's method).

    Also thank you for your replies....

  6. #6
    Captain Crash brewbuck's Avatar
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    Nobody noticed this problem?

    Code:
    for(int i=5;i>=0;i++)
        {
          n.index=i;
          n.count=i;
          chk.push_back(n);
        }
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  7. #7
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by brewbuck View Post
    Nobody noticed this problem?

    Code:
    for(int i=5;i>=0;i++)
        {
          n.index=i;
          n.count=i;
          chk.push_back(n);
        }
    Hmm... no I didn't.
    Oddly enough I haven't written any backwards loops recently.

  8. #8
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    Wink

    Oh sorry ... I forgot to mention .. I corrected the mistake but dint quite bother about it till it successfully got compiled ....

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