Question

我试图在C ++上创建一个单链表。我这样做有3个函数，它们根据结构“DiseaseList”创建一个项目，将该项目添加到列表中，然后将其打印出来。

我一直在梳理这段代码几个小时，我似乎无法阻止它将此列表的头部定位到最后一项。只有2个点可以改变头部（头部= *），但它只是对我正在写的东西的误解，我无法弄明白。

比如说我添加了两个新元素，“1”和＆amp; “2”。它将永远输出“2”循环。请结束我的痛苦:(

#include <iostream>
using namespace std;

typedef struct DiseaseList
{
    int a;
    struct DiseaseList *Next;

}DList; //Not sure if I needed DList here or should have just used DiseaseList

DList* CreateElement();
void printList(DList*);
DList* AddElement(DList*, DList*);



int main(void)
{
int choose;
DList *Head = NULL, *NewElement;
do {

cout << "1. Add element" << endl;
cout << "2. Print list" << endl;
cout << "3. Exit" << endl;
cin >> choose;
switch (choose)
{
    case 1: 
        NewElement = CreateElement();
        Head = AddElement(Head, NewElement); 
        break;
    case 2: printList(Head); break;
    case 3: return 0;
}
} while (1);

}

DList* CreateElement() //Creates a new item for the list
{
    DList* temp;

    cout << "New Number:";
    cin >> temp->a;
    temp->Next = NULL;
    return temp;
}

DList* AddElement(DList *Head, DList *NewElement) //Adds new item from CreateElement to the list
{

if (Head == NULL)
{
    NewElement->Next = NULL;
    Head = NewElement;

}
else{

DList *temp = Head;
while (temp->Next != NULL)
{
    temp = temp->Next;
}
    temp->Next = NewElement;

}
return Head;
}

void printList(DList* Head)
{
    while (Head != NULL)
{
    cout << Head->a << endl;
    Head = Head->Next;
}

}

Answer 1

CreateElement实际上并没有创建元素！

这意味着它正在返回（并使用）一个未初始化的指针，我很惊讶你的编译器没有显示警告。

替换此行：

DList* temp;

与

DList* temp = new Dlist;

Answer 2

除了@ TheDark的答案之外，您应该注意Head参数永远不会在main()中更改，除非您指定AddElement()的返回值，因为您已经[＆1;}按值重新传递指针：

DList* AddElement(DList *Head, DList *NewElement)  {

最好通过引用传递Head指针以使其正确初始化

void AddElement(DList*& Head, DList *NewElement)  {
                   // ^ Note the &
    // ...
}

Answer 3

只需要小修复（也清理空白区域）：

#include <iostream>
using namespace std;

typedef struct DList_
{
    int a;
    struct DList_ *Next;
}DList;

DList* CreateElement();
void printList(DList*);
DList* AddElement(DList*, DList*);

int main(void)
{
int choose;
DList *Head = NULL, *NewElement;
    do {
        cout << "1. Add element" << endl;
        cout << "2. Print list" << endl;
        cout << "3. Exit" << endl;
        cin >> choose;
        switch (choose)
        {
        case 1: 
            NewElement = CreateElement();
            Head = AddElement(Head, NewElement); 
            break;
        case 2: printList(Head); break;
        case 3: return 0;
        }
    } while (1);
    return 0;
}

DList* CreateElement() //Creates a new item for the list
{
    DList* temp = new DList;
    cout << "New Number:";
    cin >> temp->a;
    temp->Next = NULL;
    return temp;
}

DList* AddElement(DList *Head, DList *NewElement) //Adds new item from CreateElement to the list
{
    if(Head == NULL)
        return NewElement;
    DList *temp = Head;
    while (temp->Next != NULL)
        temp = temp->Next;
    temp->Next = NewElement;
    return Head;
}

void printList(DList* Head)
{
    while (Head != NULL)
    {
        cout << Head->a << endl;
        Head = Head->Next;
    }
}

单链表的头一直在列表中的最后一项

3 个答案: