Struct in linked list

Recently, when looking at the code , It's a little strange to find a linked list , I didn't see a reason at all , So I looked at it curiously and seriously , So I recorded this blog post .

First look at the usage ：

void threadProc()
{
    ListNode *node = sFdList.head;
    while(node)
    {
        ReactorSocket *reactor = (ReactorSocket*)node;
        
        //to do
        printf("socket fd = %d, reactor addr = %p\n", reactor->socket->sockFd, reactor);

        node = node->next;
    }
}

node Points to the head node of the linked list , And then in while Take out from circulation , And then force it to ReactorSocket* type . here node The type of is pointing to ListNode Pointer to type ,ListNode For the definition of ：

typedef struct node
{
	struct node *prev;
	struct node *next;
}ListNode;

ReactorSocket For the definition of ：

typedef struct reactorSock
{
	ListNode node;
	CSocket *socket;
}ReactorSocket;

  At first glance, see how to node The conversion of type to ReactorSocket？ Actually, adding linked list nodes is , It's added like this ：

void addReactor(List *list, ReactorSocket *reactor)
{
    printf("add node addr: %p\n", &reactor->node);
	addListNode(list, &reactor->node);
}

void addListNode(List *list, ListNode *node)
{
	list->nodeTotal++;
	node->next = NULL;
	node->prev = NULL;

	if(list->tail) // Add node to tail 
	{
		list->tail->next = node; // The tail node next Point to a new node 
		node->prev = list->tail; // New nodes prev Point to the tail node 
		list->tail = node;		 // Update tail node , Now? node It's the tail node 
	}
	else // First node 
	{
        list->head = node;
        list->tail = node;
	}
}

One of them is ：addListNode(list, &reactor->node); It's a ReactorSocket The variable of node The address is added to the linked list , Actually node My address is ReactorSocket The address of , So it can be converted in this way ：ReactorSocket *reactor = (ReactorSocket*)node;

Complete code ：

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/socket.h>

// Node definition 
typedef struct node
{
	struct node *prev;
	struct node *next;
}ListNode;

typedef struct list
{
	int nodeTotal;
	ListNode *head; // Chain head 
	ListNode *tail;	// Chain tail 
}List;

// In the function pointer defined below , The parameters of its function have void*, Its function is to bring objects in 
typedef struct
{
	uint32_t sockFd;
	int32_t (*sockSend)(void *, const char *buf, uint32_t len);
	int32_t (*sockRecv)(void *, char *buf, uint32_t len);
	int32_t (*sockClose)(void *);
	void (*sockDestory)(void *);
}CSocket;


typedef struct reactorSock
{
	ListNode node;
	CSocket *socket;
}ReactorSocket;

void addReactor(List *list, ReactorSocket *reactor);
void addListNode(List *list, ListNode *node);
void threadProc();
int32_t createSock(ReactorSocket *reactor);

static List sFdList;

struct Test
{
    char a;
    int b;
    long c;
};

int main()
{
    ReactorSocket *reactor = (ReactorSocket*)malloc(sizeof(ReactorSocket));
    int32_t fd = createSock(reactor);
    addReactor(&sFdList, reactor);

    threadProc();

    if(fd > 0)
    {
        close(fd);
    }
    
    free(reactor->socket);
    free(reactor);

    printf("sizeof(Test) = %lu\n", sizeof(long));
    return 0;
}


void addReactor(List *list, ReactorSocket *reactor)
{
    printf("add node addr: %p\n", &reactor->node);
	addListNode(list, &reactor->node);
}

void addListNode(List *list, ListNode *node)
{
	list->nodeTotal++;
	node->next = NULL;
	node->prev = NULL;

	if(list->tail) // Add node to tail 
	{
		list->tail->next = node; // The tail node next Point to a new node 
		node->prev = list->tail; // New nodes prev Point to the tail node 
		list->tail = node;		 // Update tail node , Now? node It's the tail node 
	}
	else // First node 
	{
        list->head = node;
        list->tail = node;
	}
}

int32_t createSock(ReactorSocket *reactor)
{
    int32_t fd = socket(AF_INET, SOCK_STREAM, 0);
    printf("create socket fd = %d\n", fd);

    reactor->socket = (CSocket*)malloc(sizeof(CSocket));
    reactor->socket->sockFd = fd;

    return fd;
}

void threadProc()
{
    ListNode *node = sFdList.head;
    while(node)
    {
        ReactorSocket *reactor = (ReactorSocket*)node;
        
        //to do
        printf("socket fd = %d, reactor addr = %p\n", reactor->socket->sockFd, reactor);

        node = node->next;
    }
}

  It can be seen from the printing that the address when adding the linked list is the same as the address taken out , So it can be converted successfully .