CODEWITHSUNDEEP
c++vectorstruct
Stephen
Stephen

Reputation: 25

cannot swap structs inside a class derived from vector

I have a class derived from vector, and its data elements hold structs. My problem is that when I attempt to use swap or any other method of moving the structs from one element to another I get errors. Here is my class and the struct:

#ifndef PRIQUEUE
#define PRIQUEUE

#include "PriQueueError.h"
#include <vector>
using std::vector;

const int EMPTY_QUEUE = 1;

template <class T>
struct qElem
{
    T Data;
    int Priority;
    qElem(T data, int priority) :Data(data), Priority(priority){};
};

template <class T, class T2>
class PriQueue : public vector<T2>
{
public:
    PriQueue(){}
    PriQueue(T data, int priority);
    void enqueue(T data, int priority);
    T dequeue() throw(PriQueueError);
    T qPeek() throw(PriQueueError);
    int qSize();
};


template <class T, class T2>
PriQueue<T, T2>::PriQueue(T data, int priority)
{
    this->enqueue(data, priority);
}
template <class T, class T2>
void PriQueue<T, T2>::enqueue(T data, int priority)
{
    qElem<T> tmp1(data, priority);
    this->push_back(tmp1);
    bool flag(false);

    if (this->qSize() > 1)
    {
        for (int i = this->qSize() - 1; i > 0 || flag == false; i--)
        {
            flag = true;
            if (tmp1.Priority < tmp2.Priority)
            {
                std::swap(this[i], this[i-1]);
                flag = false;
            }
        }
    }
}
template <class T, class T2>
T PriQueue<T, T2>::dequeue() throw(PriQueueError)
{
    if (this->empty())
        throw PriQueueError("Empty Queue!");

    T tmp = this->qPeek();
    this->pop_back();
    return tmp;
}
template <class T, class T2>
T PriQueue<T, T2>::qPeek() throw(PriQueueError)
{
    if (this->empty())
        throw PriQueueError("Empty Queue!");

    qElem<T> tmpStruct = this->back();
    T tmpData = tmpStruct.Data;
    return tmpData;
}
template <class T, class T2>
int PriQueue<T, T2>::qSize()
{
    return this->size();
}

#endif

The enqueue function is a bit messy because of the constant changes I have made to it to make it work. Everywhere I read it says that to access the data member of the vector you would just use nameofclass[index].member or this[index].member. In my main when I create an instance of the class (qInt) I can access the struct using qInt[index].Data, but I cannot via this[index].Data. When I am inside enqueue and try to swap(this[index], this[anotherIndex]) it errors. When I try pull up the information on this[0] and this[1] inside the debugger watch window which should give me the first and second index location of the vector, it tells me that everything is inside this[0]. I am lost on what im doing here, my class is derived from vector and therefore should act like a vector I thought, but it seems to not be doing that at all.

Upvotes: 0

Views: 95

Answers (1)

M.M
M.M

Reputation: 141554

Deriving from vector (or any other standard container) is a bad idea. They're designed to be class members ; you should make a member variable of type vector<T2> instead. The derivation doesn't gain anything, but it does introduce problems (slicing, deleting through base class pointer, awkward syntax in your member functions, etc).

Your immediate issue is that this is a pointer, so instead of this[0] you need (*this)[0], or this->operator[](0).

Upvotes: 3

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