Sort a list of pointers to objects using lambda expression

Question

I am trying to sort a list of pointers to Pilot’s objects by the times they take to compete in a race. Times are computed through compete method in class Pilot. So I will be sorting them by a method rather than a class attribute. Classes involved in the problem:

class Pilot
{
    double compete(Race *race); // Computes the time the pilot takes to finish the race
}
class Race
{
    list<Pilot*> pilots; // Pilots competing

    void sortByTime();
}

I want to sort the list using a lambda expression. Here is my try:

void Race::sortByTimes()
{ 
    sort(pilots.begin(), pilots.end(), [this](Pilot *p1, Pilot *p2) -> bool
    {
        return p1->compete(this) < p2->compete(this);
    });
}

I got 5 compile errors in algorithm library:

Error C2784 'unknown.type std::operator - (std::move_iterator<_RanIt> &, const std::move_iterator<_RanIt2> &)' : could not deduce template argument for 'std::move_iterator<_RantIt> &' from 'std::_List_iterator<std::_List_val<std::_List_simple_types<PilotoOficial*>>>'

Two more C2784 errors in std:: reverse_iterator and std::_Revranit

Error C2676 binary : 'std::_List_iterator<std::_List_val<std::_List_simple_types<Pilot*>>>' : does not define this operator or a conversion to a type acceptable to the predefined operator

Error C2780 'void std::_Sort(_RanIt,_RanIt,_Diff,_Pr' : expects 4 arguments; 3 provided

You do not need the -> bool after your lambda arguments

Cory Kramer
– Cory Kramer

2015-06-03 17:02:56 +00:00
Commented Jun 3, 2015 at 17:02 — Cory Kramer
– Cory Kramer, Commented Jun 3, 2015 at 17:02

Qaz · Accepted Answer · 2015-06-03 17:02:49Z

3

Use std::list::sort. std::sort requires random-access iterators and you've given it bidirectional iterators. The other option would be to use a container like std::vector that has random-access iterators.

answered Jun 3, 2015 at 17:02

Qaz

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