Question

I got a parent class call

Shape

Shape got 2 child call

Square and Rectangle

Shape class got a variable call area, which is of int type

So i created some object of Square, Rectangle like this

int main()
{
    Shape *shaped[100];

    //then i did some adding of object..
    int areaValue;
    areaValue=1;

    shaped[0] = new Rectangle();
    shaped[0]->setArea(areaValue);

    areaValue=7;
    shaped[1] = new Square();
    shaped[1]->setArea(areaValue);

    areaValue=5;
    shaped[2] = new Square();
    shaped[2]->setArea(areaValue);

    shapeCounter = 3;

    sort(shaped[0],shaped[2]);

    for (int i=0;i<shapeCounter;i++)
    {
        cout << shaped[i].getArea() << endl;
    }

}

I try to sort by ascending area but it doesnt work. no position change, the area still in the same sequence.

Thanks for all help!

Update:

I did the following changes at Shape.cpp

 bool Shape::orderByArea(const Shape* lhs, const shape* rhs)
    {
      return lhs->area() < rhs->area();
    }

Then at main.cpp I did this

std::sort(shaped, shaped + 3, orderByArea);

however i get an error, orderByArea was not declared in this scope.

Another thing i tried was:
To sort using vector

At Shape.h

public:

bool operator<const Shape& x) const
{
return area < x.area;
}

At main.cpp

vector<ShapeTwoD*> sortVector;
sortVector.clear();
sortVector.assign(shaped,shaped + shapeCounter);

sort(sortVector.begin(),sortVector.end());

for(int i=0;i<shapeCounter;i++)
{
cout << sortVector[i].toDisplay() << endl;
}

But nothing seems sorted. I try do a printout its position is same.

Updates: Its fixed now. sort is working . Thanks to the experts !

I got another question is

Shape *shaped[100];

How do i copy the value of

Shape *shaped[100];

into

vector<Shape> myVector;

instead of

vector<Shape*> myVector;

so i can use the normal object sort.

Answer 1

In your code how did you expect the compiler to know that you wanted to sort by area, magic? I would recommend reading a book on the standard C++ library (aka the STL), it will explain how to do custom sorting. In your code you have an array of pointers, so you should write a functor that can order your pointers. Also your parameters to std::sort are wrong. Your array starts at shaped, and ends at shaped + 3 (since you have three elements in your array).

struct sort_by_area
{
    static bool operator()(Shape* x, Shape* y)
    {
        return x->getArea() < y->getArea();
    }
};

sort(shaped, shaped + 3, sort_by_area());

Untested code, apologies for any mistakes.

Or you can use a function pointer as juanchopanza says.