Question

我正在做一个涉及链接列表的家庭作业，我遇到了Pop（）函数问题。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--;
}

我在运行程序时不断收到此运行时错误，在if语句处打破：

在作业7中的0x008e2009处未处理的异常 - CS201.exe：0xC0000005：访问冲突读取位置0x00000004。

我的一位朋友建议从程序中删除m_top = NULL，这使得if语句有效。我宁愿保持null值不变，但它让程序移动了。无论如何，它会在while循环中出现此错误：

作业7中的0x00b91f4a处的未处理异常 - CS201.exe：0xC0000005：访问冲突读取位置0xfeeefeee。

我用cout语句测试了它，错误来自while循环体; ptrNode = ptrNode->m_next。我真的不确定如何解决这个问题。任何建议都将不胜感激。

此外，如果有帮助的话，这是我程序的大部分内容：

部首：

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++;
}

主：

#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;
}

Answer 1

这是一个循环链表吗？如果没有，你为什么要在循环中进行测试：

while ( ptrNode->m_next != m_top )

不是：

while ( ptrNode->m_next != NULL )

如果是，你为什么要设置：

ptrNode->m_next = NULL;

而不是“原创”m_top-＆gt; next ??

Answer 2

你只确认第一次进入循环

while ( ptrNode->m_next != m_top )
    {
        ptrNode = ptrNode->m_next;
    }

ptrNode不会为NULL，因为你在if块中检查了它，但是当第二次进入循环时，ptrNode可能为NULL，因为现在它实际上是

m_top->m_next->m_next

但是如何确保m_top-＆gt; m_next不为NULL，当它为NULL时，它会崩溃

也许你应该把它改成

while ( ptrNode->m_next != NULL )
{
    ptrNode = ptrNode->m_next;
}

另外，还有另一个问题，在你推功能

else
{
    m_top->m_next = newNode;
    m_top = newNode;
}

应该是

else
{
    newNode->m_next = m_top;
    m_top = newNode;
}

Stack Pop（）函数的未处理异常错误

2 个答案: