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!!!!!

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.

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.

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;
}

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....

Nobody noticed this problem?

Code:

for(int i=5;i>=0;i++)
    {
      n.index=i;
      n.count=i;
      chk.push_back(n);
    }

Originally Posted by brewbuck

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.

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