C++ Sorting Custom Objects in a list

Question

I am having trouble sorting a list of custom class pointers. The class I need to sort are events. These get assigned a random time and I need to do them in the right order.

#include <list>

Class Event{
public: 
float time; // the value which I need to sort them by
int type; // to indicate which event i'm dealing with

Event(float tempTime, int tempType)
{
    time = tempTime;
    type = tempType; 
}


int main(){

std::list<Event*> EventList;
list<Event*>::iterator it;

.........

If you could help me sort this out it would be much appreciated! I've been stuck on this for hours now.

Thanks!

Answer 1

Since the list contains pointers, rather than objects, you'll have to provide a custom comparator to compare the objects they point to. And since you're using a list, you have to use its own sort method: the generic std::sort algorithm only works on random-access sequences.

EventList.sort([](Event * lhs, Event * rhs) {return lhs->time < rhs->time;});

or, if you're stuck in the past and can't use lambdas:

struct CompareEventTime {
    bool operator()(Event * lhs, Event * rhs) {return lhs->time < rhs->time;}
};

EventList.sort(CompareEventTime());

If the list contained objects (as it probably should), then it might make sense to provide a comparison operator instead:

bool operator<(Event const & lhs, Event const & rhs) {return lhs.time < rhs.time;}

std::list<Event> EventList;
//...
EventList.sort();