Question

I am trying to print the contents of a queue as an array. I have the code working and compiling. The problem is when I call the function more than once the print function does not call and the array is not printed again. I need to print the array more than once and it does not print.

The code for the Print function is :

template <class Type>
 void queueType<Type>::debugArray() 
 {
   for(queueFront; queueFront<count; queueFront++){
    cout << "[" << queueFront<< "] ," << list[queueFront] << " ";
   }

 } //end debugQueue

The main.cpp code is:

#include <iostream>
#include "queueAsArray.h"

using namespace std;

int main()
{
    queueType<int> q1;
    queueType<int> q2;
    queueType<int> q3;
    int x = 5;

    for(int i= 0; i<10; i++) {
        q1.addQueue(i);
    }

    cout << "q1 after being filled up with 10 items" << endl;

    q1.printQueueInfo();

    cout << "Queue contents from front to rear\n\n" << endl;

    q1.debugArray();
    q1.deleteQueue();
    q1.deleteQueue();
    q1.deleteQueue();

    for(int i= 0; i<=20; i){
        i+=5;
        q1.addQueue(i);
    }

    q1.debugArray();
    return 0;
}

Is there a reason why the function call will not print again? If you need the entire class and implementation file I can supply it. The weird thing is if I create a second instatiation of the class q2, then build an array for q2, the debugQueue function prints that queue. I then call the overloaded assignment operator and do q2=q1, then call debugQueue Again and it prints the contents of the queue. So I am confused as why it will print the second queue twice, but not the first queue.
Any thoughts?

Answer 1

It looks like your problem is that you’re mutating the queueType instance as a part of the printing.

template <class Type>
void queueType<Type>::debugArray() 
{
  for(queueFront; queueFront<count; queueFront++){
    cout<<"[" << queueFront<<"] ,"<< list[queueFront]<<" ";}
} 

Here you are taking the member queueFront and mutating it forward until you hit the end of the queue. This is mutating the field queueFront instead of a local which points to the same location. Try using a local and it will fix your problem

for(auto current = queueFront; current < count; current++){
  cout<<"[" << current<<"] ,"<< list[current]<<" ";}
} 

Note: I used auto for the type because I didn’t know the type of queueFront. I assume it’s list<int>::iterator but wasn’t sure. You can replace auto with the correct type or leave it as is and let the compiler infer the type of current