Question

My program is to print the queue of information from a file but i have problem with my following code. When i run the program it keep loop. I cant figure out the problem. Any help?

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <queue>
#include <list>
using namespace std;

void simulation(ifstream &infile);
void processArrival(int *newEvent, ifstream &inFile, list<int> eventList,queue<int> printQueue);
void processDeparture(int *newEvent, list<int> eventList,queue<int> printQueue);
    string name[100];
    int timeAccepted[100];
    int fileSize[100];
    int i = 1;
    int j = 1;

int currentTime;
bool checker = true;
int main(void)
{

    ifstream inFile;
    string fileName;

    int i = 0;
    inFile.open("123.txt", ios::in);

    simulation(inFile);
    /*while(inFile.peek() != EOF )

    {
        inFile>>name[i]>>timeAccepted[i]>>fileSize[i];
        i++;
    }

    for(int s = 0; s < i; s++)
    {
        cout << name[s] << timeAccepted[s] <<  fileSize[s] <<endl;
    }*/
    return 0;
}


void simulation(ifstream &inFile)
{
    queue<int> printQueue;
    list<int> eventList;

    int *newEvent;
    while(inFile.peek() != '\n')
    {
        inFile>>name[0]>>timeAccepted[0]>>fileSize[0];



    }



    eventList.push_front(timeAccepted[0]);
    int checkEmpty = eventList.empty();
    newEvent = &eventList.front();
    while(checkEmpty ==0)
    {

         newEvent = &eventList.front();


        if(checker)
        {
            processArrival(newEvent, inFile, eventList, printQueue);

        }

        else
        {
            processDeparture(newEvent, eventList, printQueue);

        }
        checkEmpty = eventList.empty();
    }


}

void processArrival(int *newEvent, ifstream &inFile, list<int> eventList,queue<int> printQueue)
{
    int atFront=0;
    atFront = printQueue.empty();
    cout << atFront <<endl;
    printQueue.push(*newEvent);
    cout << printQueue.front() <<endl;
    eventList.remove(*newEvent);

    int temp;

    if(atFront==1)
    {
        currentTime = *newEvent + fileSize[0];
        cout << name[0] << " @@ " << *newEvent << " @@ " << currentTime << endl;
        eventList.push_back(currentTime);



    }
    checker = false;
    if(inFile.peek() != EOF )
    {

        inFile>>name[i]>>timeAccepted[i]>>fileSize[i];

        eventList.push_back( timeAccepted[i] );
        i++;

        checker = false;
        if(eventList.back() <= eventList.front())
        {
            temp = eventList.back();
            eventList.back() = eventList.front();
            eventList.front() = temp;
            checker = true;
        }
    }





}

void processDeparture(int *newEvent, list<int> eventList,queue<int> printQueue)
{
    printQueue.pop();
    eventList.pop_front();
    int checkEmpty = 1;
    checkEmpty = printQueue.empty();
    int temp;
    if(checkEmpty ==0)
    {
        currentTime = *newEvent + fileSize[j];
        cout << name[j] << " " << *newEvent << " " << currentTime << endl;
        eventList.push_back(currentTime);
        checker = true;
        if(eventList.back() < eventList.front())
        {
            temp = eventList.back();
            eventList.back() = eventList.front();
            eventList.front() = temp;
            checker = false;
        }
        j++;
    }

}

Answer 1

Your processArrival and processDeparture functions are taking their eventList and printQueue arguments by value. This means that when you call them, for example in this line:

processArrival(newEvent, inFile, eventList, printQueue);

Copies of eventList and printQueue are made and passed into the processArrival function. The processArrival function then operates on those copies, and the original data is never modified. In particular, this means that the original eventList will never have any items removed from it, so it will never be empty — it will just keep trying to process the first event over and over again.

The solution is to pass these parameters by reference. i.e. change the definition of processArrival to

void processArrival(int *newEvent, ifstream &inFile, list<int>& eventList, queue<int>& printQueue)

Note the & characters that I have inserted before eventList and printQueue. These cause references to the original data, rather than copies of the original data, to be passed into the processArival function. This means that processArrival will operate directly on the original data as you intend it to. Don’t forget to make the corresponding change to processDeparture as well.