Sorting an input array of objects in C++

Question

I have a base class Shape, and other derived classes Circle, Square and Triangle. I created vector of three base-class pointers.

vector < Shape * > shapes( 3 );
shapes[ 0 ] = &C1; //Circle C1;
shapes[ 1 ] = &S1; //Square S1;
shapes[ 2 ] = &T1; //Triangle T1;

After that, I used a loop to call virtualViaPointer() that would call the virtual function draw()

for (size_t i = 0; i < shapes.size(); ++i) {
    cout << endl;
    virtualViaPointer( shapes[ i ] );
}

void virtualViaPointer(const Shape * const baseClassPtr)
{
baseClassPtr->draw();
}

Each derived class has a function getArea() that calculates the area of each shape and returns the result.

Now, I want to sort the areas by using the vector above, and calling getArea() functions. How can I do that? For example, my sort function should be like this sortShape(Array, numShape), where Array is an array of Shape pointers pointing to the created shapes.

Any help is appreciated

juanchopanza · Accepted Answer · 2012-07-23 09:47:12Z

3

You can use std::sort with a suitable comparison function:

bool compareArea(const Shape* lhs, const Shape* rhs){
  return lhs->getArea() < rhs->getArea();
}

...

std::sort(shapes.begin(), shapes.end(), compareArea);

answered Jul 23, 2012 at 9:47

juanchopanza

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Comments

MadScientist · Accepted Answer · 2012-07-23 09:46:43Z

1

Use the sort algorithms with a user-defined sorting criterion, e.g.

std::sort(shapes.begin(), shapes.end(), [](Shape * lhs, Shape * rhs)
{
  return lhs->getArea() < rhs->getArea();
});

answered Jul 23, 2012 at 9:46

MadScientist

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2 Comments

Kos Over a year ago

This is cool but please also note that it requires a modern compiler.

betabandido Over a year ago

It would be good to state that using a lambda function is only supported C++11.

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