hi, cppers:

It is said that member function can be as parameter of STL algorithm.
BUT when I pass member function whose parameter is a instance of the
class, it dose not work.

class Point
{
public:
    int x; int y;
    Point(int xx, int yy)
    {
        x = xx;
        y = yy;
    }
    friend ostream& operator<<(ostream& out,const Point& p)
    {
        out << p.x << " "<< p.y << endl;
        return out;
    }
    bool LargeThan(const Point& p)
    {

        return (x > p.x)|| ((x==p.x) && (y > p.y));
    }
    void print()
    {
        cout << x << " " << y;
    }
    void printWithPre(const char* s)
    {
        cout << s << " " << x;
    }
};
int main()
{
    vector<Point> vec;

    for (int i = 0; i < 10; i++)
        vec.push_back(Point(i, i));

    for_each(
        vec.begin(),
        vec.end(),
        bind2nd(mem_fun_ref(&Point::printWithPre),"hello:")
        );   // OK


    for_each(
 vec.begin(),
 vec.end(),
 mem_fun_ref(&Point::print)); // OK
    sort(vec.begin(), vec.end(), mem_fun_ref(&Point::LargeThan));  //
ERROR


    return 0;
}

what is the reason?

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On Jul 18, 6:40 pm, many_years_after <shua...@gmail.com> wrote:
> hi, cppers:
>
> It is said that member function can be as parameter of STL algorithm.
> BUT when I pass member function whose parameter is a instance of the
> class, it dose not work.
>
> class Point
> {
> public:
>     int x; int y;
>     Point(int xx, int yy)
>     {
>         x = xx;
>         y = yy;
>     }
>     friend ostream& operator<<(ostream& out,const Point& p)
>     {
>         out << p.x << " "<< p.y << endl;
>         return out;
>     }
>     bool LargeThan(const Point& p)
>     {
>
>         return (x > p.x)|| ((x==p.x) && (y > p.y));
>     }
>     void print()
>     {
>         cout << x << " " << y;
>     }
>     void printWithPre(const char* s)
>     {
>         cout << s << " " << x;
>     }};
>
> int main()
> {
>     vector<Point> vec;
>
>     for (int i = 0; i < 10; i++)
>         vec.push_back(Point(i, i));
>
>     for_each(
>         vec.begin(),
>         vec.end(),
>         bind2nd(mem_fun_ref(&Point::printWithPre),"hello:")
>         );   // OK
>
>     for_each(
>         vec.begin(),
>         vec.end(),
>         mem_fun_ref(&Point::print)); // OK
>     sort(vec.begin(), vec.end(), mem_fun_ref(&Point::LargeThan));  //
> ERROR
>
>     return 0;
>
> }
>
> what is the reason?

Your comparison function must take both parameters as const

  Jiri Palecek

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