Thread: Homework Help - Create FIFO Queue class

The assignment says to "Create a Queue class that implements a queue abstraction."

Naturally, I'm running into errors:
main_Hardesty.cpp:30:25: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
QueueItem_Hardesty.cpp: In constructor ‘QueueItem::QueueItem(char*, int)’:
QueueItem_Hardesty.cpp:31:47: error: incompatible types in assignment of ‘char*’ to ‘char [30]’
QueueItem_Hardesty.cpp:33:21: error: ‘pDate’ was not declared in this scope

I'm copying my elements incorrectly, but I'm not knowledgeable enough to fix it. Can you assist? Thank you.

Here's the relevant stuff from my cpp file

Code:

#include <iostream>         //my standard cout/cin stuff
#include <cstdio>           //some C stuff for good measure
#include <iomanip>          //the setfill() and setw() stuff
#include <string>           //self-explanatory
#include "QueueItem_Hardesty.h"  /*include my QueueItem_Hardesty header 
                                  file with class QueueItem*/
#include "Queue_Hardesty.h"      /*include my Queue_Hardesty.h file with 
                                   class Queue*/
using std::cout;
using std::cin;
using std::endl;
using std::setfill;
using std::setw;
using std::string;
using std::copy;

//***LINE 29*** my QueueItem constructor
QueueItem::QueueItem(char *pData, int id)
   : _data (pData), _itemID (id), _pNext (NULL)  //private variables now global variables
{
   std::copy(_data, *pDate + 30, std::begin(pDate));
}  //end constructor/function

And my header file

Code:

//***LINE 13*** Prevent multiple inclusions of header
#ifndef QueueItem_H
#define QueueItem_H

//this will set/get data members, not manipulate the linked lists
class QueueItem
{
public: 
   QueueItem(char *pData, int id);        //ctor
   void setNext(QueueItem *pItem);        //set pointer to next Item
   QueueItem* getNext() const;            //get pointer for next Item
   int getId() const;                     //get Id
   const char* getData() const;

private:
   char _data[30];              //data value character string/array
   const int _itemID;           //unique ID for item in queue
   QueueItem* _pNext;           //next item in queue
}; //end class QueueItem

#endif

Crap, you need my main function.

Code:

#include <iostream>
#include <iomanip>
#include <string>
using std::cout;
using std::endl;
using std::setfill;
using std::setw;
using std::string;

#include "Queue_Hardesty.h"

int main()
{
   //***LINE 25*** construct a queue called myQueue
   Queue myQueue;
   cout << "Creating a queue.  Program is now started." << endl;
   myQueue.removeItem();      //call Remove, should do nothing since Queue is empty

   myQueue.addItem("red");    //
   myQueue.addItem("green");
   myQueue.addItem("blue");
   myQueue.addItem("orange");
   myQueue.print();           //prints contesnts of queue (ID & data)
   myQueue.removeItem();
   myQueue.removeItem();

/*...
  etc, etc, etc
  ...*/

} //end function main

Why are you trying to use C-strings instead of std::strings? You seem to know about this class, since you included the <string> header.


Jim

Whelp, I clearly don't get what I'm supposed to do because I switched my QueueItem.h to read "std::string _data;" instead of "char _data[30];" but I'm still getting the same errors as before. What did I miss from the instructions?

Errors:

Code:

main_Hardesty.cpp: In function ‘int main()’:
main_Hardesty.cpp:30:25: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
(THE ABOVE ERROR OCCURS FOR EVERY TIME I CALL myQueue.addItem IN main)
QueueItem_Hardesty.cpp: In member function ‘const char* QueueItem::getData() const’:
QueueItem_Hardesty.cpp:53:11: error: cannot convert ‘const string {aka const std::basic_string<char>}’ to ‘const char*’ in return

Here's the amended QueueItem.h

Code:

//***LINE 13*** Prevent multiple inclusions of header
#ifndef QueueItem_H
#define QueueItem_H

//this will set/get data members, not manipulate the linked lists
class QueueItem
{
public: 
   QueueItem(char *pData, int id);        //ctor
   void setNext(QueueItem *pItem);        //set pointer to next Item
   QueueItem* getNext() const;            //get pointer for next Item
   int getId() const;                     //get Id
   const char* getData() const;

private:
   std::string _data;           //data value character string/array
   const int _itemID;           //unique ID for item in queue
   QueueItem* _pNext;           //next item in queue
}; //end class QueueItem

#endif

And my QueueItem.cpp

Code:

#include <iostream>         //my standard cout/cin stuff
#include <cstdio>           //some C stuff for good measure
#include <iomanip>          //the setfill() and setw() stuff
#include <string>           //self-explanatory
#include "QueueItem_Hardesty.h"  /*include my QueueItem_Hardesty header 
                                  file with class QueueItem*/
#include "Queue_Hardesty.h"      /*include my Queue_Hardesty.h file with 
                                   class Queue*/
using std::cout;
using std::cin;
using std::endl;
using std::setfill;
using std::setw;
using std::string;
using std::copy;

//my QueueItem constructor
QueueItem::QueueItem(char *pData, int id)
   : _data (pData), _itemID (id), _pNext (NULL)  //private variables now global variables
{
   //std::copy(_data, pData + 30, std::begin(pData));
}  //end constructor/function

...

const char* QueueItem::getData() const
{
   return _data;
}  //***LINE 54*** end getData function

If I haven't said it before, I appreciate your help as I crawl through this.

Aaaannd, lest I forget my main.cpp

Code:

#include <iostream>
#include <iomanip>
#include <string>
using std::cout;
using std::endl;
using std::setfill;
using std::setw;
using std::string;

#include "Queue_Hardesty.h"

int main()
{
   //construct a queue called myQueue
   Queue myQueue;
   cout << "Creating a queue.  Program is now started." << endl;
   myQueue.removeItem();      //call Remove, should do nothing since Queue is empty

   myQueue.addItem("red");    //
   myQueue.addItem("green");
   myQueue.addItem("blue");
   myQueue.addItem("orange");
   myQueue.print();           //prints contesnts of queue (ID & data)
   myQueue.removeItem();
   myQueue.removeItem();
   myQueue.addItem("black");
   myQueue.addItem("brown");
   myQueue.addItem("gray");
   myQueue.addItem("purple");
   myQueue.print();
   myQueue.removeItem();
   myQueue.removeItem();
   myQueue.removeItem();
   myQueue.removeItem();
   myQueue.print();
   myQueue.eraseQueue();
   myQueue.addItem("white");
   myQueue.addItem("tan");
   myQueue.addItem("pink");
   myQueue.print();
   myQueue.eraseQueue();
   myQueue.print();

} //end function main

Why the char *? Shouldn't tese be strings not char *?

Code:

...
   const char* getData() const;
...
QueueItem::QueueItem(char *pData, int id)

(THE ABOVE ERROR OCCURS FOR EVERY TIME I CALL myQueue.addItem IN main)

So where is addItem()?

Jim

So, if I change every instance of "char *pData" to "std::string pData", will this break my linked list?

Here's the addItem() code given to us by the instructor.

Code:

//dynamically create and init a new QueueItem object
void Queue::addItem(char *pData)
{
   QueueItem *pItem = new QueueItem(pData, ++_itemCounter);

   if (pHead == 0)   //check for an empty queue
      pHead = pTail = pItem;
   else               //link new item onto end of list using _pTail pointer
   {
      pTail->setNext(pItem);
      pTail = pItem;
   } 
}  //end addItem function

Your thoughts?

If you examine the documentation, you can indeed put a constant char pointer into the std::string constructor so it is valid to construct std::string with const char* or char* which will automatically be interpreted as constant.

I'm not sure what your structure actually looks like (I'm just skimming the topic) but your nodes should look like this :

Code:

struct queue_node {

      std::string data;
      queue_node *next;
};

You can easily initialize data with a char*.

Thank you all very much for your patience and hand-holding. You've earned your mitzvah wings today!