c++ - 将项目插入我的排序列表时出现问题？

Question

因此，我构建了一个排序的链表并进行了编译和所有爵士乐，我插入第一个项目很好，但是当我尝试插入第二个项目时，我得到这个错误:[main] 1000 ( 0) handle_exceptions: Exception: STATUS_ACCESS_VIOLATION 我做了一些搜索，发现它可能与我的插入函数或我的 IsFull 函数有关(我应该只能将 10 个项目插入列表中) - 但对于我的生活，我无法弄清楚它有什么问题。也许这里有人可以帮忙？ (我不确定发布全部代码是否有帮助，但无论如何我都会这样做)

美国橄榄球联盟.h

#include <string>
const int MAX_ITEMS = 10;
enum RelationType  {LESS, GREATER, EQUAL};

using namespace std;
#ifndef NFL_H
#define NFL_H
struct NFL {
        string firstName;
        string lastName;
        string currentTeam;
        string position;
        string school;
};
#endif

排序的NFL.cpp

#include "sortedNFL.h"

struct NodeType
{
  NFL player;
  NodeType* next;
};

SortedNFL::SortedNFL()  // Class constructor
{
  length = 0;
  nflList = NULL;
}

bool SortedNFL::IsFull() const
{
  if (length == MAX_ITEMS || length > MAX_ITEMS)
  {
    return true;
  }
  else
    return false;
  /*NodeType* location;
  try
  {
    location = new NodeType;
    delete location;
    return false;
  }
  catch(std::bad_alloc exception)
  {
    return true;
  }*/
}

int SortedNFL::GetLength() const
{
  return length;
}

void SortedNFL::MakeEmpty()
{
  NodeType* tempPtr;

  while (nflList != NULL)
  {
    tempPtr = nflList;
    nflList = nflList->next;
    delete tempPtr;
  }
  length = 0;
}

NFL SortedNFL::GetItem(NFL& playerRequested, bool& found)
{
  bool moreToSearch; //flag for more items to search
  NodeType* location; 

  location = nflList; //initial location is first item in NFL list
  found = false; //flag for if item is found
  moreToSearch = (location != NULL);

  while (moreToSearch && !found) //while there is more to search and item is not found
  {
    if (playerRequested.lastName.compare(location->player.lastName) > 0)
    {
      location = location->next;
      moreToSearch = (location != NULL);
    }
    if (playerRequested.lastName.compare(location->player.lastName) == 0 && playerRequested.firstName.compare(location->player.firstName) == 0)
    {
      found = true; 
      playerRequested = location->player;
    }
    if (playerRequested.lastName.compare(location->player.lastName) < 0)
    {
      moreToSearch = false;
    }
  }
  return playerRequested;
}

void SortedNFL::PutItem(NFL inputPlayer)
{
  NodeType* newNode;    // pointer to node being inserted
  NodeType* predLoc;    // trailing pointer
  NodeType* location;   // traveling pointer
  bool moreToSearch;

  location = nflList;
  predLoc = NULL;
  moreToSearch = (location != NULL);

  // Find insertion point.
  while (moreToSearch) //while moreToSearch is true
  {
    if (inputPlayer.lastName.compare(location->player.lastName) > 0)
    {
      predLoc = location;
      location = location->next;
      moreToSearch = (location != NULL);
    }
    if (inputPlayer.lastName.compare(location->player.lastName) < 0)
    {
      moreToSearch = false;
    }    
  }

  // Prepare node for insertion
  newNode = new NodeType;
  newNode->player = inputPlayer;
  // Insert node into list.
  if (predLoc == NULL)         // Insert as first
  {
    newNode->next = nflList;
    nflList = newNode;
  }
  else
  {
    newNode->next = location;
    predLoc->next = newNode;
  }
  length++;
}
/*void SortedNFL::DeleteItem(NFL playerDeleted)
{
  NodeType* location = nflList;
  NodeType* tempLocation;

  // Locate node to be deleted.
  if (playerDeleted.lastName.ComparedTo(nflList->player) == EQUAL)
  {
    tempLocation = location;
    nflList = nflList->next;    // Delete first node.
  }
  else
  {
    while (playerDeleted.lastName.ComparedTo((location->next)->player) != EQUAL)
      location = location->next;

    // Delete node at location->next
    tempLocation = location->next;
    location->next = (location->next)->next;
  }
  delete tempLocation;
  length--;
}*/

void SortedNFL::ResetList()
{
  currentPos = NULL;
} 

NFL SortedNFL::GetNextItem()
{
  NFL playerRequested;
  if (currentPos == NULL)
    currentPos = nflList;
  playerRequested = currentPos->player; 
  currentPos = currentPos->next;
  return playerRequested;

} 
SortedNFL::~SortedNFL() //class destructor
{
  NodeType* tempPtr;

  while (nflList != NULL)
  {
    tempPtr = nflList;
    nflList = nflList->next;
    delete tempPtr;
  }
}

Answer 1

让我们看看 GetItem() 中的主循环:

if (inputPlayer.lastName.compare(location->player.lastName) > 0)
{
  predLoc = location;
  location = location->next;
  moreToSearch = (location != NULL);
}

假设 location 指向链表中的最后一个元素，比较结果为 true。因此，在 if 语句中，您会将 NULL 放入 location，这是列表中的最后一个元素。

那么紧接着会发生什么？

if (inputPlayer.lastName.compare(location->player.lastName) < 0)

繁荣。空指针取消引用。未定义的行为。