结构中typedef的奇怪行为

Strange behaviour of typedef in struct

本文关键字：typedef 结构更新时间：2023-10-16

我在C++中制作了一个singly linked list的程序，所以在类中使用了struct。我知道typedef与struct一起使用，因此之后声明不需要使用struct关键字。但是，当我不使用typedef时，即使在未来的声明中不使用struct关键字，代码也会成功编译，但当我使用typedef时，它不会编译。这是代码：

#include <iostream>
using namespace std;
struct node{        
    int data;
    node* next;
}*head; 
class single_list{
    public:
        struct node* create_node(int);
        void insert_begin();
        void insert_pos();
        void insert_last();
        void delete_pos();
        void sort();
        void display();
};
int main()
{
    int choice,nodes,element,position,i;
    single_list sl;
    node* head = NULL;
    while(1)
    {
        cout<<endl<<"List of operations"<<endl;
        cout<<"1: Insert node at the beginning"<<endl;
        cout<<"2: Insert node at a specific position"<<endl;
        cout<<"3: Insert node at the last"<<endl;
        cout<<"4: Delete a node at specific position"<<endl;
        cout<<"5: Sorting the linked list"<<endl;
        cout<<"6: Display the linked list"<<endl;
        cout<<"Enter your choice"<<endl;
        cin>>choice;
        switch(choice)
        {
            case 1:
                cout<<"Inserting node at the beninning"<<endl;
                sl.insert_begin();
                cout<<endl;
                break;
            case 2:
                cout<<"Inserting node at a specific position"<<endl;
                sl.insert_pos();
                cout<<endl;
                break;
            case 3:
                cout<<"Inserting node at the last place"<<endl;
                sl.insert_last();
                cout<<endl;
                break;
            case 4:
                cout<<"Deleting node at specific position"<<endl;
                sl.delete_pos();
                cout<<endl;
                break;
            case 5:
                cout<<"Sorting the linked list"<<endl;
                sl.sort();
                cout<<endl;
                break;
            case 6:
                cout<<"Displaying the linked list"<<endl;
                sl.display();
                cout<<endl;
                break;
            default:
                cout<<"Wrong Choice"<<endl;                     
        }
    }
}
node *single_list::create_node(int data)
{
    node* temp;
    temp = new node;
    temp->data = data;
    temp->next = NULL;
    return temp;
}
void single_list::insert_begin()
{
    cout<<"Enter value to be inserted"<<endl;
    int data;
    cin>>data;
    node* temp;
    node* p;
    temp = create_node(data);
    if (head == NULL)
    {
        head = temp;
        head->next = NULL;
    }
    else
    {
        p = head;
        head = temp;
        head->next = p;
    }
}
void single_list::insert_pos()
{
    cout<<"Enter the position at which you want to enter the number"<<endl;
    int pos;
    cin>>pos;
    cout<<"Enter the data of the node"<<endl;
    int data;
    node* t;
    t = head;
    node* temp1;
    temp1->data = data;
    for(int i=1;i<pos;i++)
    {
        t = t->next;
    }
    if(pos == 1)
    {
        if(head == NULL)
        {
            head = temp1;
            head->next = NULL;
        }
        else
        {
            temp1->next = t->next;
            t->next = temp1;    
        }
    }
    else
    {
        cout<<"Position out of range"<<endl;
    }
}
void single_list::insert_last()
{
    cout<<"Enter the data of the number"<<endl;
    int data;
    cin>>data;
    node* temp1;
    temp1->data = data;
    temp1->next = NULL;
    node* t;
    t = head;
    while(t != NULL)
   {
        t = t->next;
   }
    t->next = temp1;
}

定义struct 后

struct node{        
    int data;
    node* next;
}*head;

在C++中，名称node可以在没有typedef的情况下使用。你一定在想C，它需要typedef。

在C++中，可以使用：

struct node{        
    int data;
    node* next;
};
node* head;

在C中，您需要使用：

struct node{        
    int data;
    struct node* next;
};
struct node* head;

或

// Define the struct and a typedef in one statement.
typedef struct node{        
    int data;
    struct node* next;
} node;
node* head;

在C++中定义/声明对象时，不需要使用struct关键字。在C中是这样，而不是在C++中。

以下代码声明head是指向node变量的指针。

struct node{        
    int data;
    node* next;
}*head;

但是，下面将把head定义为指向node的类型指针的别名。

typedef struct node{        
    int data;
    node* next;
}*head;