出于某种原因，当我将列表输出到文本文件时，我得到了所有节点，除了还有一个额外的空白节点被添加到列表的开头，如下所示：
(blank), (blank) $(blank)
Ball, 20 $9.99
我该如何解决这个问题？我尝试在while循环之后删除head并将nodePtr / head递增到 - ，但无济于事。
#include <iostream>
#define nullptr 0
#include <cstdlib>
#include <algorithm>
#include <string>
#include <conio.h>
#include <fstream>
using namespace std;
class ItemList {
private:
struct ListNode{
string IName;
string QQuantity;
string PPrice;
struct ListNode * next;
};
ListNode *head;
public:
ItemList()
{
head = new ListNode;
head->next=nullptr;
}
~ItemList();
void insertNode(string Item, string Quantity, string Price)
{
ListNode *newNode;
ListNode *nodePtr;
ListNode *previousNode=nullptr;
newNode=new ListNode;
newNode->IName=Item;
newNode->QQuantity=Quantity;
newNode->PPrice=Price;
if(!head)
{
head=newNode;
newNode->next=nullptr;
}
else
{
nodePtr=head;
previousNode=nullptr;
while(nodePtr != nullptr && nodePtr->IName < Item)
{
previousNode=nodePtr;
nodePtr=nodePtr->next;
}
if(previousNode==nullptr)
{
head=newNode;
newNode->next=nodePtr;
}
else
{
previousNode->next=newNode;
newNode->next=nodePtr;
}
}
}
void displayNode()
{
ListNode *nodePtr;
nodePtr=head->next;
int i=0;
if(head->next==nullptr)
{
cout << "The store is empty." << endl;
}
while(nodePtr)
{
i++;
cout << i << ". " << nodePtr->IName << ", ";
cout << nodePtr->QQuantity << " ";
cout << "$" << nodePtr->PPrice << "\n" << endl;
nodePtr=nodePtr->next;
}
}
void modifyNode(string Item)
{
ListNode *nodePtr;
ListNode *nodePrev;
string newName, newQuantity, newPrice;
int modify;
if (head==nullptr)
{
return;
}
else
{
nodePtr = head;
if (head->IName==Item)
nodePtr = head->next;
else
{
while (nodePtr != nullptr && nodePtr->IName != Item)
{
nodePrev = nodePtr;
nodePtr = nodePtr->next;
}
}
if (nodePtr)
{
system("cls");
cout << nodePtr->IName << "\t" << nodePtr->QQuantity << "\t" << nodePtr->PPrice << endl;
cout << "What would you like to change?\n";
cout << "1. Item" << endl;
cout << "2. Quantity" << endl;
cout << "3. Price" << endl;
cout << "4. Whole Entry" << endl;
cin >> modify;
switch (modify)
{
case 1:
cout << "Change to what?\n";
cin.sync();
getline(cin,newName);
transform(newName.begin(), newName.end(), newName.begin(), ::toupper);
nodePtr->IName = newName;
break;
case 2:
cout << "Change to what?\n";
cin >> newQuantity;
nodePtr->QQuantity = newQuantity;
break;
case 3:
cout << "Change to what?\n";
cin >> newPrice;
nodePtr->PPrice = newPrice;
break;
case 4:
cout << "What is the product called?\n";
cin.sync();
getline(cin,newName);
transform(newName.begin(), newName.end(), newName.begin(), ::toupper);
nodePtr->IName = newName;
cout << "How many are there really?\n";
cin >> newQuantity;
nodePtr->QQuantity = newQuantity;
cout << "What is the actual price?\n";
cin >> newPrice;
nodePtr->PPrice = newPrice;
}
newName=nodePtr->IName;
newQuantity=nodePtr->QQuantity;
newPrice=nodePtr->PPrice;
deleteNode(newName);
insertNode(newName, newQuantity, newPrice);
cout << "Entry successfully changed." << endl;
}
else
cout << "Product not found\n";
}
}
void deleteNode(string Item)
{
ListNode *nodePtr;
ListNode *previousNode;
if(!head)
return;
if(head->IName==Item)
{
nodePtr=head->next;
delete head;
head=nodePtr;
}
else
{
nodePtr=head;
while(nodePtr!=nullptr && nodePtr->IName!=Item)
{
previousNode=nodePtr;
nodePtr=nodePtr->next;
}
if(nodePtr)
{
previousNode->next=nodePtr->next;
delete nodePtr;
}
else
{
cout << "Nothing to delete." << endl;
}
}
}
void deleteRangeNode(int start, int stop)
{
ListNode *nodePtr;
ListNode *newNode;
nodePtr = head;
int i=-1;
cin.sync();
while(nodePtr!=nullptr)
{
i++;
if((i>=start)&&(i<=stop))
{
newNode->next = nodePtr -> next;
cout << "Deleted Product: " << nodePtr->IName << endl;
delete nodePtr;
nodePtr=newNode;
}
newNode=nodePtr;
nodePtr=nodePtr->next;
}
}
void displayRange()
{
ListNode * nodePtr;
nodePtr=head;
int i=-1;
int start, stop;
if(head->next==nullptr)
{
cout << "The store is empty." << endl;
}
else
{
cout << "The display should START at: ";
cin >> start;
cout << "The display should END at: ";
cin >> stop;
system("cls");
while(nodePtr!=nullptr)
{
i++;
if((i>=start && i<=stop))
{
cout << i << ". " << nodePtr->IName << ", ";
cout << nodePtr->QQuantity << " ";
cout << "$" << nodePtr->PPrice << "\n" << endl;
}
nodePtr=nodePtr->next;
}
}
}
void deleteAllNodes()
{
ListNode *temp = head;
while(head->next!=nullptr)
{
temp=head->next;
free(head);
head=temp;
}
}
void keepNodes()
{
ofstream FinalInventory;
FinalInventory.open("store.txt");
ListNode *nodePtr;
nodePtr=head;
while(nodePtr!=nullptr)
{
FinalInventory << nodePtr->IName << ", " << nodePtr->QQuantity << " $" << nodePtr->PPrice << endl;
nodePtr=nodePtr->next;
}
delete head++;
FinalInventory.close();
}
};
ItemList::~ItemList()
{
ListNode *nodePtr;
ListNode *nextNode;
nodePtr=head;
while(nodePtr!=nullptr)
{
nextNode=nodePtr->next;
delete nodePtr;
nodePtr=nextNode;
}
}
int main()
{
int menu();
ItemList pro;
int method;
while(method!=0)
{
int method=menu();
system("cls");
string It, Q, P;
int begin, end;
switch(method)
{
case 1:
int count;
cout << "How many products would you like to put in?" << endl;
cin >> count;
system("cls");
for(int i=0; i<count; i++)
{
cout << "Product #" << i + 1 << endl;
cout << "Enter the item name: ";
cin.sync();
getline(cin,It);
transform(It.begin(), It.end(), It.begin(), ::toupper);
cout << "Enter the Quantity: ";
cin >> Q;
transform(Q.begin(), Q.end(), Q.begin(), ::toupper);
cout << "Enter the Price: ";
cin >> P;
pro.insertNode(It, Q, P);
cout << "\n";
}
break;
case 2:
int dis;
cout << "How many products would you like to display?" << endl;
cout << "1. Entire Store" << endl;
cout << "2. Range of Products" << endl;
cin >> dis;
system("cls");
switch(dis)
{
case 1:
pro.displayNode();
break;
case 2:
system("cls");
pro.displayRange();
break;
}
break;
case 3:
pro.displayNode();
cout << "What product do you wish to modify? (by item name)" << endl;
cin.sync();
getline(cin, It);
transform(It.begin(), It.end(), It.begin(), ::toupper);
pro.modifyNode(It);
break;
case 4:
int del;
cout << "Do you wish to delete one product or more?" << endl;
cout << "1. One" << endl;
cout << "2. Range of Products" << endl;
cout << "3. Entire Store" << endl;
cin >> del;
system("cls");
switch(del)
{
case 1:
cout << "What product do you wish to delete? (by item name)" << endl;
pro.displayNode();
cin.sync();
getline(cin,It);
transform(It.begin(), It.end(), It.begin(), ::toupper);
pro.deleteNode(It);
cout << "\nItem successfully deleted." << endl;
cout << "\n";
break;
case 2:
pro.displayNode();
cout << "What range of items do you wish to delete? (by number)" << endl;
cout << "START: ";
cin >> begin;
cout << "END: ";
cin >> end;
pro.deleteRangeNode(begin, end);
break;
case 3:
pro.deleteAllNodes();
cout << "All items deleted." << endl;
break;
}
break;
case 5:
pro.keepNodes();
cout << "The inventory has been saved." << endl;
break;
case 0:
cout << "Exiting the program." << endl;
return 0;
}
system("pause");
system("cls");
}
return 0;
}
int menu()
{
string space1= " ";
string space2= " ";
int method;
cout << space1 << "What would you like to do to the store's inventory?" << endl;
cout << space2 << "1. Add Product" << endl;
cout << space2 << "2. Display Products" << endl;
cout << space2 << "3. Modify Product" << endl;
cout << space2 << "4. Delete Product" << endl;
cout << space2 << "5. Save Inventory" << endl;
cout << space2 << "0. Exit\n" << endl;
cout << space2;
cin >> method;
return(method);
}
答案 0 :(得分：0)
这是因为您的ItemList构造函数总是在列表的开头插入一个新节点：
ItemList()
{
head = new ListNode;
head->next=nullptr;
}
节点的字段是std::string s，默认构造为所有空格。然后继续创建列表，添加其他节点。然后打印整个列表。这就是你在输出中看到的，在列表的开头。
如果你怀疑我，you should ask your rubber duck。
答案 1 :(得分：0)
你在另一个地方问了同样的问题，并且还指出了解决方案/修复方法。你检查过了吗？