Question

I can’t seem to figure out the syntax for finding structs in containers.

I have a multiset of Event structs. I’m trying to find one of these structs by searching on its key. I get the compiler error commented below.

struct Event {
 public:
  bool operator < ( const Event & rhs ) const {
    return ( time < rhs.time );
  }
  bool operator > ( const Event & rhs ) const {
    return ( time > rhs.time );
  }
  bool operator == ( const Event & rhs ) const {
    return ( time == rhs.time );
  }

  double time;
  int eventID;
  int hostID;
  int s; 
};

typedef std::multiset< Event, std::less< Event > > EventPQ;

EventPQ currentEvents;
double oldRecTime = 20.0;
EventPQ::iterator ceItr = currentEvents.find( EventPQ::key_type( oldRecTime ) ); // no matching function call

I’ve tried a few permutations to no avail. I thought defining the conditional equality operator was going to be enough.

---

Solution

After correcting my typo (sorry), I now have a solution closest to AraK’s, augmented by Soapbox’s suggested use of explicit:

struct Event { 
   explicit Event(double t) : time(t), eventID(), hostID(), s() {}
   Event(double t, int eid, int hid, int stype) : time(t), eventID( eid ), hostID( hid ), s(stype) {}
   ... 
};

EventPQ::iterator ceItr = currentEvents.find( EventPQ::key_type( Event(oldRecTime) ) ); 

I recently discovered that another option would have been to use find_if, discussed here.

Thanks for the help.

Answer 1

You don’t have a suitable constructor that accepts double. Just add the following constructor:

Event(double t) : time(t), eventID(/**/), hostIDeventID(/**/), s(/**/)
{ }

Here is how Event would look like:

struct Event {
 public:
 // Initialize other variables as needed
 Event(double t) : time(t), eventID(/**/), hostIDeventID(/**/), s(/**/)
 { }

  bool operator < ( const Event & rhs ) const {
    return ( time < rhs.time );
  }
  bool operator > ( const Event & rhs ) const {
    return ( time > rhs.time );
  }
  bool operator == ( const Event & rhs ) const {
    return ( time == rhs.time );
  }

  double time;
  int eventID;
  int hostID;
  int s; 
};

// No need for std::less because it is used by default,
// when you define 'operator <' in your class
typedef std::multiset< Event > EventPQ;

EventPQ currentEvents;
double oldRecTime = 20.0;
// You can just pass the double, a temporary object will be created
// for you.
EventPQ::iterator ceItr = currentEvents.find( oldRecTime );