I'm trying to iterate through a deque and erase the element with the smallest arrivalTime. The function works the first couple of times, then gives me the "iterator not dereferencable" error and stops working.

My Processor.h:

#pragma once

#include <deque>
#include "Job.h"
#include <ctime>

using namespace std;

class Processor {
public:
    deque<Job> priorityQueue;
    Job runningJob;
    bool isProcessing;
    int processingTime;
    int runningTime;
    int overallJobs;
    int numJobs[4];     //0 is A, 1 is B, 2 is C, 3 is D
    int runningJobNumber;
    int interruptedJobs;

    Processor();

    void simulate();

    Job findNextJob();
};

My findNextJob():

Job Processor::findNextJob() {
    Job nextJob = priorityQueue.front();

    deque<Job>::const_iterator iter = priorityQueue.begin();
    deque<Job>::const_iterator location;

    while (iter <= priorityQueue.end()) {
        if (iter->arrivalTime < nextJob.arrivalTime) {
            nextJob = *iter;
            location = iter;
            iter++;
        }
        else {
            iter++;
        }
    }

    priorityQueue.erase(location);

    return nextJob;
}

And finally, where I'm calling the function:

void Processor::simulate() {
    srand(time(NULL));

    char newJobType;

    while (processingTime <= 50) {
        newJobType = 65 + rand() % 4;
        Job newJob(newJobType);
        newJob.arrivalTime += runningTime;

        processingTime += newJob.processingTime;

        priorityQueue.push_back(newJob);
        cout << endl << newJob.type << " " << newJob.arrivalTime;
        runningTime++;
    }
    runningTime = 0;

    int jobFinishTime;
    Job nextJob;

    nextJob = findNextJob();

    while (priorityQueue.size()) {
        cout << endl << runningTime << ") " << "Queue size: " << priorityQueue.size();
        if (!isProcessing) {
            cout << " CPU 1 Idle;";

            if (nextJob.arrivalTime == runningTime) {
                runningJob = nextJob;

                //irrelevant code here

                nextJob = findNextJob();
            }
        }

        if (isProcessing && (runningJob.arrivalTime + runningJob.processingTime) != runningTime) {

            //irrelevant code here

            if (nextJob.arrivalTime <= runningTime) {
                runningJob = nextJob;

                //irrelevant code here

                nextJob = findNextJob();
            }
        }
        if (nextJob.priority > runningJob.priority && nextJob.arrivalTime <= runningTime) {
                //irrelevant code here
        }



        runningTime++;
    }



}

findNextJob() runs successfully two or three times then gives me the error. Any help would be appreciated.

1 Answers

1
Kevin Chen On Best Solutions

In C++, the end iterator "points to" one past the last element.

findNextJob allows the iterator iter to become equal to priorityQueue.end(), so dereferencing it is invalid.

while (iter <= priorityQueue.end()) {
    // ...
}