Sorting STL vector

How do I sort a STL vector containing my own class.

I have a class called CObject and a vector
vector<CObject> Objects

In CObject is a function called GetYPos().
I need to sort the vector so that the Objects with the lowest YPos are first.

I tried using std::sort with the operator < overloaded in CObject but it doesn't work.

Is there any other solutions?

Thanks

The overloaded operator < and std::sort method is the easiest. What kind of errors were you getting?

Code:

---

#include <iostream>
#include <vector>
#include <algorithm>

class MyObject
{
        int m_x;
public:
        MyObject& operator=(int x)
        {
                m_x = x;
                return *this;
        }
        bool operator<(const MyObject& rhs)
        {
                return (m_x < rhs.m_x);
        }
        void Print()
        {
                std::cout << m_x << " ";
        }
};

int main(void)
{
        std::vector<MyObject> vec(4);
        int i;

        vec[0] = 8;
        vec[1] = 5;
        vec[2] = 0;
        vec[3] = 2;

        for(i = 0;i < vec.size();++i)
        {
                vec[i].Print();
        }

        std::cout << std::endl;

        std::sort(vec.begin(),vec.end());

        for(i = 0;i < vec.size();++i)
        {
                vec[i].Print();
        }

        std::cout << std::endl;

        return 0;
}

---

passing `const CObject' as `this' argument of `bool CObject::operator<(const CObject&)' discards qualifiers

stl_algo.h:2118: instantiated from `void std::__introsort_loop(_RandomAccessIter, _RandomAccessIter, _Size) [with _RandomAccessIter = __gnu_cxx::__normal_iterator< CObject*, std::vector< CObject, std::allocator< CObject> > >, _Size = int]'

First off, does your overloaded < operator work outside of the sort function like if you just tested it in main?

Yes, it does.

Hmmmm.... post the relevant code, that might help.

The member function must be const.
It should look like this.

Code:

---

bool CObject::operator<(const CObject&) const

---

My second post on the following thread answers a very similiar question, and shows why the function signature looks like it does.

http://www.cprogramming.com/cboard/s...const+operator