1. 宏观

目的：实现简单的TCP通信

我们需要server.c 和 client.c

2. server.c

/*
 * socket
 * bind
 * listen
 * accept
 * send/recv
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>

#define SERVER_PORT    8888
#define BACKLOG        10

int main(int argc, char **argv)
{
	int server;
	int client;
	struct sockaddr_in server_addr;
	struct sockaddr_in client_addr;
	int ret;
	int server_recv;
	int addr_len;
	
	unsigned char recvbuf[1000];

	int client_num = -1;
	//signal(SIGCHLD, SIG_IGN);  /* 处理僵死进程 */

	/* 句柄 */
	server = socket(AF_INET, SOCK_STREAM, 0);
	if (server == -1){
		printf("soket error!\n");	
		return -1;
	}

	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(SERVER_PORT);
	server_addr.sin_addr.s_addr = INADDR_ANY;
	memset(server_addr.sin_zero, 0, 8);
	/* 将文件句柄绑定ip和端口*/
	ret = bind(server, (const struct sockaddr *)&server_addr, 
						sizeof(struct sockaddr));
	if (ret == -1){
		printf("bind error!\n");
		return -1;
	}

	/* 开始检测 */
	ret = listen(server, BACKLOG);
	if (ret == -1){
		printf("listen error!\n");
		return -1;
	}

	while (1) {
		/* 等待客户端连接*/
		addr_len = sizeof(struct sockaddr);
		client = accept(server, (struct sockaddr *)&client_addr, &addr_len);
		if (client != -1){
			client_num++; /* 统计客户端*/
			printf("get connect form client %d : %s \n", client_num, 
					inet_ntoa(client_addr.sin_addr));
			/* 支持多个客户端连接，对每个连接创建一个子进程 */
			if (!fork()){
				/* 子进程 */
				while (1){
					/* 接受客户端发来的数据 */
					server_recv = recv(client, recvbuf, 999, 0);
					if (server_recv <= 0){
						close(client);
						return -1;
					} else {
						recvbuf[server_recv]= '\0';
						printf("get msg form %d : %s\n", client_num, recvbuf);
					}
				}
			}
		}
	}

	close(server);

	return 0;
}

3. client.c

/*
 * socket
 * connect
 * send/recv
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

#define SERVER_PORT    8888   /* 端口和server.c 保持一致 */

int main(int argc, char **argv)
{
    int client;
    struct sockaddr_in server_addr;
    int ret;
    unsigned char sendbuf[1000];
    int client_send;

    if (argc != 2){
        printf("Usage: %s <server_ip>\n", argv[0]);
        return -1;
    }

    /* 创建句柄 */
    client = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(SERVER_PORT);
	//server_addr.sin_addr.s_addr = INADDR_ANY;
    if (inet_aton(argv[1], &server_addr.sin_addr) == 0){
        printf("invalid server_ip\n");
        return -1;
    }
	memset(server_addr.sin_zero, 0, 8);
    /* 连接服务器 */
    ret = connect(client, (const struct sockaddr *)&server_addr,
                   sizeof(struct sockaddr));
    if (ret == -1){
        printf("connect error!\n");
        return -1;
    }

    while (1){
         if (fgets(sendbuf, 999, stdin)){
            /* 发送数据给服务器 */
            client_send = send(client, sendbuf, strlen(sendbuf), 0);
            if (client_send <= 0){
                close(client);
                return -1;
            }
         }
    }

    return 0;
}

4. 实验

整体流程：client1和client2和server进行通讯，然后ps -a 查看进程。(开4个窗口)

5. END