Stack Pop(）函数出现未处理的异常错误

我正在做一项涉及链表的家庭作业，Pop（）函数有问题。这是我的代码：

void CardStack::Pop( )
{
    if ( m_top->m_next == NULL )
    {
        delete m_top;
        m_top = NULL;
    }
    else
    {
        Node* ptrNode = m_top;
        // gets 2nd to last node
        while ( ptrNode->m_next != m_top )
        {
            ptrNode = ptrNode->m_next;
        }
        // delete last node, then set second to last to null
        delete m_top;
        m_top = NULL;
        ptrNode->m_next = NULL;
        m_top = ptrNode;
    }
    m_size--;
}

当我运行程序时，我不断地得到这个运行时错误，破坏了if语句：

分配7中0x008e2009处出现未处理的异常-CS201.exe：0xC0000005:读取位置0x00000004时发生访问冲突。

我的一个朋友建议从程序中删除m_top = NULL，这样if语句就可以工作了。我宁愿保持空值不变，但它让程序移动了。无论如何，它会在while循环中出现以下错误：

分配7中0x00b91f4a处出现未处理的异常-CS201.exe：0xC0000005:读取位置0xfeeefeee时发生访问冲突。

我用cout语句测试了它，错误来自while循环的主体；CCD_ 2。我真的不知道该怎么解决这个问题。如有任何建议，我们将不胜感激。

此外，如果有帮助的话，下面是我程序的大部分剩余部分：

标题：

class Node
{
public:
    friend class CardStack;
private:
    Node* m_next;
    int m_data;
};
class CardStack
{
public:
    CardStack();
    ~CardStack();
    void Push( int value );
    void Pop();
    int Top();
    int GetSize();
private:
    int m_size;
    Node* m_top;
};

构造函数、析构函数、Push（）:

#include <iostream>
#include "CardStack.h"
using namespace std;
CardStack::CardStack( )
{
    m_top = NULL;
    m_size = 0;
}
CardStack::~CardStack( )
{
    while ( m_top != NULL )
    {
        Pop( );
    }
}
void CardStack::Push( int value )
{
    //creates new node
    Node* newNode = new Node;
    newNode->m_data = value;
    newNode->m_next = NULL;
    // tests if the list is empty
    if ( m_top == NULL )
    {
        m_top = newNode;
    }
    // if the list does contain data members and a last node exists
    else
    {
        m_top->m_next = newNode;
        m_top = newNode;
    }
    m_size++;
}

Main：

#include <iostream>
#include <string>
#include <fstream>
#include "CardStack.h"
using namespace std;
void loadDeck ( ifstream&, CardStack& );
void playGame ( CardStack& );
void loadDeck ( ifstream& inFile, CardStack *card )
{
    int currentCard;
    while( !inFile.eof() )
    {
        inFile >> currentCard;
        card->Push( currentCard );
    }
}
void playGame( CardStack *card )
{
    int score[ 4 ];
    int player;
    while( card->GetSize() != 0 )
    {
        player = card->GetSize() % 4;
        score[ player ] += card->Top();
        card->Pop();
    }
    for ( player = 0; player < 4; player++ )
        cout << "Player " << player << "'s score is " << score[ player ] << endl;
}
int main()
{
    CardStack *card = new CardStack;
    string fileName;
    ifstream inFile;
    do
    {
        cout << "Input the name of the card file (not including extension): ";
        cin >> fileName;
        fileName += ".txt";
        inFile.open( fileName );
        if ( !inFile.is_open() )
            cout << "File could not be opened. Reenter the file name." << endl;
    }
    while( !inFile.is_open() );
    loadDeck( inFile, card );
    playGame( card );
    inFile.close();
    system( "pause" );
    return 0;
}