Sorting an array of objects using the result of a function in the object in c++

Question

I have a program that creates an array of pointers to an object. The class the pointers are pointing to stores the net price of an item and has a function for calculating the gross price of the object.

Product *p[10];

Book *b;
Software *s;

double price;

cout << "Enter the price of the book: " << endl;
cin >> price;

b = new Book(price);

cout << "Enter the price of the software: " << endl;
cin >> price;

s = new Software(price);

cout << "Gross price of book: " << b->getGrossPrice() << endl;
cout << "Gross price of software: " << s->getGrossPrice() << endl;

p[0] = b;
p[1] = s;

Is there a way of sorting the array in ascending order of the gross price?

I know there is a sort algorithm in the STL but I don't think it will work for me or at least I'm not sure how to make it work.

There are solutions to similar problems on the site that use sort however none that I can find show it's used in this context.

is getGrossPrice() virtual? then you can just call sort with a custom functor that calls that — Hatted Rooster
– Hatted Rooster, Commented Jan 25, 2017 at 19:24

Armen Tsirunyan · Accepted Answer · 2017-01-25 19:28:55Z

4

std::sort(p, p+n,
          [](Product* p1, Product* p2)
          {
              return p1->getGrossPrice() < p2->getGrossPrise();
          });

This is a call to the standard sorting function std::sort. We pass the begin and end iterators(pointers, in this case) to the range we with to sort, and a third argument which is a function object that returns true its first argument is strictly less (in terms of the strict weak ordering we want to sort according to) than the second argument and false otherwise. The part that starts with [] is called a lambda-expression: in other languages similar objects can be known as anonymous functions. It was introduced in C++11.

edited Jan 25, 2017 at 19:28

answered Jan 25, 2017 at 19:25

Armen Tsirunyan

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5 Comments

mascoj Over a year ago

Amen, Please don't just post code. This is not helpful for the asker to understand the answer. If you can, edit the answer and add a brief explanation.

Hatted Rooster Over a year ago

Might want to add C++11 > and maybe add a solution for pre.

Armen Tsirunyan Over a year ago

Have a little patience, guys.

François Andrieux Over a year ago

@ArmenTsirunyan Regarding your plea for patience : it's reasonable to assume that once someone posts an answer, it's the complete answer they intended to post. People are right to critic an answer immediately.

Captain Giraffe Over a year ago

@FrançoisAndrieux On the other hand the SO system encourages First to post, so Armens procedure is a common one. It is also encouraged by Jon Skeet.

Jarod42 · Accepted Answer · 2017-01-25 21:08:11Z

0

With range-v3, you can simply do (with projection):

ranges::sort(prods, std::less<>{}, &Product::getGrossPrice);

Demo

answered Jan 25, 2017 at 21:08

Jarod42

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