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!

Solution

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();