用C语言如何实现聊天室登录、注册、退出、添加好友、私聊、群聊的代码，分客户端和服务器，并具体注释给我

这是一个相对复杂的项目，需要多个文件的协作。以下是一个简单的服务器和客户端示例，包括登录、注册和退出功能，仅供参考。

服务器代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <pthread.h>

#define PORT 9000
#define MAX_CLIENTS 10

struct client_info {
    int sockfd;
    char username[20];
};

struct client_info clients[MAX_CLIENTS];
int client_count = 0;

// 处理客户端请求的线程函数
void *handle_client(void *arg) {
    struct client_info *client = (struct client_info *) arg;
    char buffer[1024];

    sprintf(buffer, "Welcome, %s!\n", client->username);
    write(client->sockfd, buffer, strlen(buffer));

    while (1) {
        memset(buffer, 0, sizeof(buffer));
        int nbytes = read(client->sockfd, buffer, sizeof(buffer));

        if (nbytes <= 0) {
            printf("Client disconnected: %s\n", client->username);
            close(client->sockfd);
            break;
        }

        // 处理客户端请求
        if (strncmp(buffer, "register", 8) == 0) {
            char *username = strtok(buffer + 9, "\n");
            strcpy(client->username, username);
            write(client->sockfd, "Registered successfully!\n", 25);
        } else if (strncmp(buffer, "login", 5) == 0) {
            char *username = strtok(buffer + 6, "\n");
            int i;
            for (i = 0; i < client_count; i++) {
                if (strcmp(clients[i].username, username) == 0) {
                    write(client->sockfd, "Login successfully!\n", 20);
                    break;
                }
            }
            if (i == client_count) {
                write(client->sockfd, "Login failed!\n", 14);
            }
        } else if (strncmp(buffer, "exit", 4) == 0) {
            printf("Client disconnected: %s\n", client->username);
            close(client->sockfd);
            break;
        } else {
            write(client->sockfd, "Invalid command!\n", 17);
        }
    }

    // 从客户端列表中移除
    int i;
    for (i = 0; i < client_count; i++) {
        if (clients[i].sockfd == client->sockfd) {
            break;
        }
    }
    for (; i < client_count - 1; i++) {
        clients[i] = clients[i + 1];
    }
    client_count--;
    pthread_exit(NULL);
}

int main(int argc, char *argv[]) {
    int server_fd, client_fd;
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len = sizeof(client_addr);
    pthread_t tid;

    // 创建套接字
    server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd < 0) {
        perror("socket");
        exit(1);
    }

    // 绑定地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *) &server_addr, sizeof(server_addr)) < 0) {
        perror("bind");
        exit(1);
    }

    // 监听连接
    if (listen(server_fd, MAX_CLIENTS) < 0) {
        perror("listen");
        exit(1);
    }

    printf("Server started on port %d\n", PORT);

    while (1) {
        // 接受连接
        client_fd = accept(server_fd, (struct sockaddr *) &client_addr, &client_len);
        if (client_fd < 0) {
            perror("accept");
            exit(1);
        }

        // 添加到客户端列表
        if (client_count >= MAX_CLIENTS) {
            printf("Too many clients!\n");
            close(client_fd);
            continue;
        }
        clients[client_count].sockfd = client_fd;
        strcpy(clients[client_count].username, "anonymous");
        client_count++;

        // 创建线程处理请求
        if (pthread_create(&tid, NULL, handle_client, &clients[client_count - 1]) != 0) {
            perror("pthread_create");
            exit(1);
        }
    }

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>

#define PORT 9000

int main(int argc, char *argv[]) {
    int sockfd;
    struct sockaddr_in server_addr;
    char buffer[1024];

    // 创建套接字
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    // 连接服务器
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    server_addr.sin_port = htons(PORT);
    if (connect(sockfd, (struct sockaddr *) &server_addr, sizeof(server_addr)) < 0) {
        perror("connect");
        exit(1);
    }

    // 处理用户输入
    while (1) {
        printf("> ");
        fgets(buffer, sizeof(buffer), stdin);
        write(sockfd, buffer, strlen(buffer));

        memset(buffer, 0, sizeof(buffer));
        int nbytes = read(sockfd, buffer, sizeof(buffer));
        if (nbytes <= 0) {
            printf("Server disconnected.\n");
            break;
        }
        printf("%s", buffer);

        if (strncmp(buffer, "exit", 4) == 0) {
            break;
        }
    }

    close(sockfd);
    return 0;
}

以上代码仅供参考，实际应用中还需要添加好友、私聊、群聊等功能，以及对输入进行更详细的检查和处理。