我出于教育目的而编写的双链表程序在语法上存在一些问题。我已经在头文件中创建了一个结构,我的主程序似乎还不错,但是在.cpp文件中实现我的功能给我带来了极大的困难。我很难辨别将记录插入列表的三种情况。具体来说,分配内存,初始化列表的开头和结尾以及语句的顺序令我感到困惑,因为传递要添加到我的列表中的记录副本也是如此。
我的头文件如下:
struct rec
{
char * id;
char firstname[15];
char lastname[15];
struct rec* prev;
struct rec* next;
};
int AddItem ( rec r );
int DeleteItem ( char* delid );
void PrintList ( int order );
困难所在的我的.cpp文件如下:
#include <iostream>
#include "list.h"
#include <string.h>
using namespace std;
// These pointers refer to the head and tail of the list.
rec* first = NULL;
rec* last = NULL;
int AddItem( Rec r )
{
rec* newRecEntry;
rec* current = NULL;
rec* previous = NULL;
// Check for duplicate id
current = first;
while (current)
{
if( strcmp(current -> id, r.id) == 0)
{
return 0;
}
else
// Create a new node
{
newRecEntry = new Rec;
newRecEntry->id = new char[strlen(r.id)+1];
strcpy(newRecEntry->id, r.id);
strcpy(newRecEntry->firstname,r.firstname);
strcpy(newRecEntry->lastname,r.lastname);
newRecEntry->next = NULL;
newRecEntry->prev = NULL;
}
// Find the appropriate position for the node and insert accordingly
// Check to see if the list is empty
if (first == NULL)
{
first = newRecEntry;
last = newRecEntry;
}
else if ( r.lastname>last.lastname)
{
else
{
return 0;
}
/*int DeleteItem(char* ID)
我应该能够在列表的开头,中间和结尾插入。根据ID从列表中删除一个项目,并根据用户输入以升序或降序打印列表,但我首先只是想处理将项目添加到所述列表中。我的函数定义如下,并且还包含一些错误
lists.cpp
#include <iostream>
#include "list.h"
#include <string.h>
using namespace std;
// These pointers refer to the head and tail of the list.
rec* first = NULL;
rec* last = NULL;
int AddItem( Rec r )
{
rec* newRecEntry;
rec* current = NULL;
rec* previous = NULL;
// Check for duplicate id
current = first;
while (current)
{
if( strcmp(current -> id, r.id) == 0)
{
return 0;
}
else
// Create a new node
{
newRecEntry = new Rec;
newRecEntry->id = new char[strlen(r.id)+1];
strcpy(newRecEntry->id, r.id);
strcpy(newRecEntry->firstname,r.firstname);
strcpy(newRecEntry->lastname,r.lastname);
newRecEntry->next = NULL;
newRecEntry->prev = NULL;
}
// Find the appropriate position for the node and insert accordingly
// Check to see if the list is empty
if (first == NULL)
{
first = newRecEntry;
last = newRecEntry;
}
else if ( r.lastname>last.lastname)
{
else
{
return 0;
}
/*int DeleteItem(char* ID)
{
rec
}
*/
/*void printList(int order)
{
loop
{
cout << ptr -> Id << " ";
cout << ptr -> firstname << " ";
cout << ptr -> lastname << " ";
cout << ptr -> prev << " "; // address of previous
cout << ptr << " "; // address of item
cout << ptr -> next << " "; // address of next item
}
}
主要如下:
#include <iostream>
#include "list.h"
#include <string.h> // <string>
using namespace std;
void main (void)
{
int choice, printorder;
char idbuffer[100];
rec r;
do
{
cout << "Enter your choice 1 Add, 2 Delete, 3 Print, 0 quit "<<endl;
cin >> choice;
switch ( choice )
{
case 1: //AddItem
cout << "\nEnter ID ";
cin >> idbuffer;
r.id = idbuffer;
cout << "\nFirst Name ";
cin >> r.firstname;
cout << "\nLast Name ";
cin >> r.lastname;
if ( AddItem ( r ) )
{
cout << "\nSuccess!\n";
}
else
{
cout << "\nItem failed to be added\n";
}
break;
case 2: //Delete
cout << "\nEnter id :";
cin >> idbuffer;
if ( DeleteItem ( idbuffer ) )
{
cout << "\nDelete OK\n";
}
else
{
cout << "\nDelete Failed for " << idbuffer;
}
break;
case 3: // Print
cout << "Enter order 0 - Ascending, 1 - Descending\n";
cin >> printorder;
PrintList (printorder);
break;
case 0: // quit
break;
default: // bad choice
break;
} // end switch
}
while ( choice != 0 );// end do while
} // end main
看起来可能不像,但即使这个功能
int AddItem(Record entry)
{
Record* newRecordPointer;
newRecordPointer=new Record;
strcpy(newRecordPointer->firstName,entry.firstName);
strcpy(newRecordPointer->lastName,entry.lastName);
newRecordPointer->ID=new char[strlen(entry.ID)+1];
strcpy(newRecordPointer->ID, entry.ID);
return 0;
}
正在尝试做太多事情。
让我们编写将项目添加到列表的伪代码描述:
我已经标记了所涉及的动词和名词,并且您已经可以看到函数中缺少名词之一。您要AddItem
将一个项目添加到列表中...但是您没有提供要处理的列表。
清楚地写出您的期望也很有用:
AddItem
被调用之前:Record
Record
AddItem
被调用后:Record
,它的Next
都应指向新节点Previous
应指向传入的节点Record
,其Next
和Previous
成员指向其自身因此,假设可能起作用的最小功能是:
void AddItem(Record *insert_after, Record value)
{
Record *new_node = CreateRecord();
CopyRecordValues(new_node, &value);
AttachAfter(insert_after, new_node);
}
[请注意,如果我们正在编写真正的C ++,则前两行仅可以使用copy构造函数Record *new_node = new Record(value)
,但是要比从我们开始的地方习惯的C ++代码进行更改,将花费更多的更改。
现在,您可以:
CreateRecord
和CopyRecordValues
已在您当前的代码中处理过)尝试更改此内容:
int AddItem(Record entry);
为此:
Record* AddItem(Record entry, Record *insertion_point = NULL );
如果insertion_point
为NULL
,则可以假定Record
是新列表的开头。
现在您有足够的信息来设置Next
和Previous
指针,并返回新创建的节点。
首先,您必须定义第一项和结束项。
可能是
Previous
分配给NULL
的项目。Next
分配给NULL
的项目结束。为简单起见,我删除了Record
的某些字段,这不是最好的,请小心,您应该执行许多错误处理并注意异常:
struct Record
{
int id;
Record* Next;
Record* Previous;
};
Record *CreateList(int id)
{
Record *rec = new Record;
rec->id = id;
rec->Next = NULL;
rec->Previous = NULL;
return rec;
}
void AddItemAfter(Record *item, int id)
{
if (!item)
return;
Record* newRecordPointer = new Record;
newRecordPointer->id = id;
newRecordPointer->Next = NULL;
newRecordPointer->Previous = NULL;
newRecordPointer->Next = item->Next;
item->Next = newRecordPointer;
newRecordPointer->Previous = item;
}
void ShowList(Record *list)
{
Record *ptr = list;
while (ptr)
{
cout << ptr->id << endl;
ptr = ptr->Next;
}
}
int main()
{
Record *list = CreateList(1);
AddItemAfter(list, 2);
AddItemAfter(list, 3);
ShowList(list);
}