Question

i’m trying to set a list by desc order, setting the highest to the front of the list, but it is not doing it, here is the struct i am using

struct  datalist
{
    short   index;
    int nNumber;

    bool operator > (const datalist& a) const
    {
        return (nNumber > a.nNumber);
    }
};

and i am doing

datalist* pAR = new datalist;
pAR->index = 1000;
pAR->nNumber = 10;
m_SomeList.push_back(pAR);

pAR = new datalist;
pAR->index = 1005;
pAR->nNumber = 30;
m_SomeList.push_back(pAR);

pAR = new datalist;
pAR->index = 0;
pAR->nNumber = 20;
m_SomeList.push_back(pAR);

m_SomeList.sort(greater<datalist*>());

after the sort, it is outputting 20, 30, 10, i am using VS 6.0, and before i get comments of i need to upgrade, i know that is an old compiler but in my case i need it, so please keep that in mind when answering, the best descriptive, helpful answer gets the vote.

Answer 1

You are sorting a container of pointers, so the container uses std::greater on the pointers so they are sorted by address in non-descending order.

You want to do something like this:

struct Comp {
    bool operator()(const datalist* a, const datalist* b) {
        return *a > *b;
    }
};

m_SomeList.sort(Comp());

or

m_SomeList.sort([](const datalist* a, const datalist* b) {
    return *a > *b;
}); // for C++11

Also as chris mentioned, you might want to be storing these objects by value instead of by pointers so you don’t have to clean them up.