operator <

stoneJax (260)
I am trying to create a program that is an event simulation using the STL priority queue. I created the operator < function inside a struct, but when I run the program I get an error that I do not know how to make sense of. I have had a link error in the past (different project), but I was using different files and I was able to get rid of it by creating a new project with one file and then splitting up the client, implementation, and header file. However, this project is all in one file.

ERROR:

Severity Code Description Project File Line Suppression State
Error LNK2019 unresolved external symbol "struct Event __cdecl processArrival(struct Event,class std::priority_queue<struct Event,class std::vector<struct Event,class std::allocator<struct Event> >,struct std::less<struct Event> >,class std::queue<struct Event,class std::deque<struct Event,class std::allocator<struct Event> > >)" (?processArrival@@YA?AUEvent@@U1@V?$priority_queue@UEvent@@V?$vector@UEvent@@V?$allocator@UEvent@@@std@@@std@@U?$less@UEvent@@@3@@std@@V?$queue@UEvent@@V?$deque@UEvent@@V?$allocator@UEvent@@@std@@@std@@@3@@Z) referenced in function "void __cdecl simulate(void)" (?simulate@@YAXXZ)


If I comment out the operator < function I'll get this error, which I think is because the priority queue by nature needs to have operator < implemented:

Severity Code Description Project File Line Suppression State
Error C2676 binary '<': 'const _Ty' does not define this operator or a conversion to a type acceptable to the predefined operator wk_11_sortedList_queues C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.25.28610\include\xstddef 127

I posting just this because that is where the problem is, but if I need to post something else please let me know.


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  struct Event
{

	int customerID;
	int transactionTime;
	int arrivalTime;
	int currentTime;

	bool operator < (const Event& right) const
	{
		return this->arrivalTime < right.arrivalTime;

	}
};
Ganado (6849)
Your error message complains about a "processArrival" function not being defined.
Last edited on
stoneJax (260)
I have it defined, but it looks like I am not using one of the given parameters. For "processArrival" all I am supposed to do is store an arrival time, and a transaction time in a bankQueue which represents the people waiting in line at a bank. I used the first parameter "newEvent" which contains the top() values from from the event list, and the third parameter bankQueue so I can push the arrivalTime and transactionTime into it. I am not seeing what I should be doing with the second parameter "eventListPQueue" though. Also, I can't even debug what I have to check on values until I get past this error as the program will not compile to a breakpoint.

I'll post what I have.

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#include <iostream>
#include <queue>
#include <fstream>
using namespace std;

class Customer
{
public:
	int customerID;
};


struct Event
{

	int customerID;
	int transactionTime;
	int arrivalTime;
	int currentTime;
	typedef int value_type;

	bool operator < (const Event& right) const
	{
		return this->arrivalTime < right.arrivalTime;

	}
};


void simulate();
Event processArrival(Event newEvent, priority_queue<Event> eventListPQueue, queue<Event> bankQueue);
Event processDeparture(Event newEvent, priority_queue<Event> eventListPQueue, queue<Event> bankQueue);

int main()
{
	simulate();
	return 0;
}





void simulate()
{
	ifstream file;
	int data;
	int newArrivalEvent = 0;
	int transactionTime = 0;
	bool tellerAvailable = true;

	
	/*Create an empty queue bankQueue to represent the bank line
	Create an empty priority queue eventListPQueue for the event list*/
	queue <Event> bankQueue;
	priority_queue <Event> eventListPQueue;

	// Create and add arrival events to event list  
	file.open("a11in1.txt");

	while (file) {                                     // data file is not empty

		file >> newArrivalEvent >> transactionTime;    // Get next arrival time aand transaction time t from file
		//cout << "test data: " << data << endl;
		cout << "test newArrivalEvent: " << newArrivalEvent << endl;
		cout << "test transactionTime: " << transactionTime << endl;

		// a new arrival event containing a and t
		Event event;
		event.arrivalTime = newArrivalEvent;
		event.transactionTime = transactionTime;
		eventListPQueue.push(event);	
	}
	file.close();
	
	
	
	// Event loop 
	int currentTime = 0;
	while (eventListPQueue.size() > 0 ) {                        // Event list is not empty

		Event newEvent;
		newEvent = eventListPQueue.top();
  
		currentTime = newEvent.arrivalTime;                      // Get current time       

		if (newEvent.arrivalTime)                                // is an arrival event
			processArrival(newEvent, eventListPQueue, bankQueue);

		else
			processDeparture(newEvent, eventListPQueue, bankQueue);

	}

	//****************  pseudiocode to fill in  **************************************

	//// Processes an arrival event. 
	//processArrival(arrivalEvent: Event, eventListPQueue : PriorityQueue, bankQueue : Queue) 
	//// Remove this event from the event list 
	//eventListPQueue.remove()    
	//
	//customer = customer referenced in arrivalEvent 
	//if (bankQueue.isEmpty() && tellerAvailable) {

	//	departureTime = currentTime + transaction time in arrivalEvent       
	//	newDepartureEvent = a new departure event with departureTime        
	//	eventListPQueue.add(newDepartureEvent)        
	//	tellerAvailable = false
	//}
	//else       
	//	bankQueue.enqueue(customer)
	//	
	//	// Processes a departure event . 
	//	+processDeparture(departureEvent: Event, eventListPQueue: PriorityQueue, bankQueue: Queue)

	//	// Remove this event from the event list 
	//	eventListPQueue.remove() 
	//	
	//	if (!bankQueue.isEmpty()) { 
	//		
	//		// Customer at front of line begins transaction 
	//		customer = bankQueue.peek()        
	//		bankQueue.dequeue()        
	//		departureTime = currentTime + transaction time in customer       
	//		newDepartureEvent = a new departure event with departureTime        
	//		eventListPQueue.add(newDepartureEvent)
	//	}
	//	else
	//		tellerAvailable = true

}





template<typename value_type>
Event processArrival(Event newEvent, priority_queue<value_type> eventListPQueue, queue<value_type> bankQueue)
{
	Event bankLine;
	bankLine.arrivalTime = newEvent;
	bankLine.transactionTime = newEvent;
	bankQueue.push(bankLine);

	return bankLine;
}
keskiverto (10425)
You have two functions:
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Event processArrival( Event, priority_queue<Event>, queue<Event> ); // #1
template<typename value_type>
Event processArrival( Event, priority_queue<value_type>, queue<value_type> ); // #2

The #1 is just a declaration for a normal standalone function. There is no implementation for it.

The #2 is a template. Furhermore, it not visible on line 89. The whole template has to be accessible when something needs to be instantiated from it. Before line 89.
stoneJax (260)
Oh sorry. I was playing around with the typedef int value_type and forgot to change the parameters for consistency. I changed everything to <Event>.

Regarding, "The whole template has to be accessible when something needs to be instantiated from it." That reminds me. The only experience I have with templates is with a client, implementation, and header file. Then the implementation file would have to be removed from the project. This project is all in one file so I am not sure about how that works. I am not even sure if I should be using a template. If the STL priority queue is a templated class, does that mean I have to make my function a template?
keskiverto (10425)
If the STL priority queue is a templated class, does that mean I have to make my function a template?

No. The priority_queue<Event> is a concrete type. Not a template.

I did remove the declaration and moved your template to before the simulate(). The I got:
 In instantiation of 'Event processArrival(Event, std::priority_queue<value_type>,
  std::queue<value_type>) [with value_type = Event;
  typename std::vector<_Tp>::value_type = Event]':

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template<typename value_type>
Event processArrival( Event newEvent,
   priority_queue<value_type> eventListPQueue,
   queue<value_type> bankQueue )
{
  Event bankLine;
  bankLine.arrivalTime = newEvent;// error: cannot convert 'Event' to 'int' in assignment
  bankLine.transactionTime = newEvent; // error: cannot convert 'Event' to 'int' in assignment
  bankQueue.push(bankLine);
  return bankLine;
}

That is not all that is odd in this function:
* You push an Event to bankQueue that holds value_type objects
* eventListPQueue is not used
* You push to bankQueue that is a local copy (it is a by value parameter)
* You set a value to only two members of bankLine.
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