代码思路

服务器

#include <stdio.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <string.h>
#include <sys/wait.h>
#include <signal.h>//链表节点结构体：
typedef struct node
{struct sockaddr_in addr; //data   memcmpstruct node *next;
} link_t;//类型
enum type_t
{login,chat,quit,
};//消息对应的结构体(同一个协议)
typedef struct msg_t
{int type;       //'L' C  Q    enum un{login,chat,quit};char name[32];  //用户名char text[128]; //消息正文
} MSG_t;link_t *link_creat();
void client_login(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr);
void client_quit(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr);
void client_chat(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr);int main(int argc, char const *argv[])
{// 创建套接字int sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (sockfd < 0){perror("socket err");return -1;}printf("sockfd:%d\n", sockfd);// 绑定struct sockaddr_in saddr, caddr;saddr.sin_family = AF_INET;saddr.sin_port = htons(atoi(argv[1]));saddr.sin_addr.s_addr = INADDR_ANY;socklen_t len = sizeof(caddr);if (bind(sockfd, (struct sockaddr *)&saddr, sizeof(saddr)) < 0){perror("bind err");return -1;}printf("bind ok\n");// 创建链表link_t *p = link_creat();printf("creat ok\n");MSG_t msg;// 可扩展功能，服务器可以给所有用户发送“公告”pid_t pid = fork();if (pid < 0){perror("fork err");return -1;}else if (pid == 0){while (1){fgets(msg.text, sizeof(msg.text), stdin);if (msg.text[strlen(msg.text) - 1] == '\n')msg.text[strlen(msg.text) - 1] = '\0';msg.type = chat;strcpy(msg.name, "server");sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&saddr, sizeof(saddr));}}else{while (1){if (recvfrom(sockfd, &msg, sizeof(msg), 0, (struct sockaddr *)&caddr, &len) < 0){perror("recvfrom err");return -1;}printf("type:%d\n", msg.type);switch (msg.type){case login: // 上线函数client_login(sockfd, p, msg, caddr);break;case chat: // 聊天函数client_chat(sockfd, p, msg, caddr);break;case quit: // 下线函数client_quit(sockfd, p, msg, caddr);break;default:break;}}}close(sockfd);return 0;
}
// 创建链表
link_t *link_creat()
{// 给头结点开辟空间link_t *p = (link_t *)malloc(sizeof(link_t));if (p == NULL){perror("malloc err");return NULL;}// 初始化头结点p->next = NULL;return p;
}// 客户端上线功能：将用户上线消息发送给其他用户，并将用户信息添加到链表中
void client_login(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr)
{printf("%s  login....\n", msg.name);// 先遍历链表// 再插入新的节点while (p->next != NULL){p = p->next;sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&(p->addr), sizeof(p->addr));}link_t *pnew = (link_t *)malloc(sizeof(link_t));pnew->addr = caddr;pnew->next = NULL;p->next = pnew;return;
}
// 聊天功能：转发消息到在链表中除了自己的所有用户
void client_chat(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr)
{printf("%s says %s\n", msg.name, msg.text);while (p->next != NULL){p = p->next;// strcmp:对比前后两个字符串中的内容是否一致// memcmp:对比前后两个对应的地址(任意类型)的内容是否一致if (memcmp(&(p->addr), &caddr, sizeof(caddr))){sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&(p->addr), sizeof(p->addr));}}return;
}
// 客户端退出功能：将用户下线消息发送给其他用户，将下线用户从链表中删除
void client_quit(int sockfd, link_t *p, MSG_t msg, struct sockaddr_in caddr)
{printf("%s quit.......\n", msg.name);link_t *pdel = NULL;while (p->next != NULL){if (memcmp(&(p->next->addr), &caddr, sizeof(caddr))){// 不是自己p = p->next;sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&(p->addr), sizeof(p->addr));}else{// 是自己,删除节点pdel = p->next;p->next = pdel->next;free(pdel);pdel = NULL;}}return;
}

客户端

#include <stdio.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <string.h>
#include <sys/wait.h>
#include <signal.h>//链表节点结构体：
typedef struct node
{struct sockaddr_in addr; //data   memcmpstruct node *next;
} link_t;//类型
enum type_t
{login,chat,quit,
};//消息对应的结构体(同一个协议)
typedef struct msg_t
{int type;       //'L' C  Q    enum un{login,chat,quit};char name[32];  //用户名char text[128]; //消息正文
} MSG_t;int main(int argc, char const *argv[])
{int ret;// 创建套接字int sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (sockfd < 0){perror("socket err");return -1;}printf("sockfd:%d\n", sockfd);// 绑定struct sockaddr_in saddr, caddr;saddr.sin_family = AF_INET;saddr.sin_port = htons(atoi(argv[2]));saddr.sin_addr.s_addr = inet_addr(argv[1]);socklen_t len = sizeof(caddr);MSG_t msg;// 给服务器发送上线消息printf("请输入用户名:");fgets(msg.name, sizeof(msg.name), stdin);if (msg.name[strlen(msg.name) - 1] == '\n')msg.name[strlen(msg.name) - 1] = '\0';msg.type = login;sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&saddr, sizeof(saddr));pid_t pid = fork();if (pid < 0){perror("fork err");return -1;}else if (pid == 0) // 循环接受服务器消息{while (1){ret = recvfrom(sockfd, &msg, sizeof(MSG_t), 0, NULL, NULL);if (ret < 0){perror("recv from err");return -1;}if (msg.type == login)printf("%s login.......\n", msg.name);else if (msg.type == chat)printf("%s says %s\n", msg.name, msg.text);else if (msg.type == quit)printf("%s quit.......\n", msg.name);}}else // 循环发送消息{while (1){fgets(msg.text, sizeof(msg.text), stdin);if (msg.text[strlen(msg.text) - 1] == '\n')msg.text[strlen(msg.text) - 1] = '\0';if (!strcmp(msg.text, "quit")){msg.type = quit;sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&saddr, sizeof(saddr));break;}else{msg.type = chat;sendto(sockfd, &msg, sizeof(MSG_t), 0, (struct sockaddr *)&saddr, sizeof(saddr));}}kill(pid, SIGINT);wait(NULL);}close(sockfd);return 0;
}