一个简单的socket服务端和客户端程序：客户端发送数据给服务端，服务端接收到数据后再给客户端发送数据

/***********server***********/

#include <netinet/in.h> // for sockaddr_in
#include <sys/types.h>  // for socket
#include <sys/socket.h> // for socket
#include <stdio.h>      // for printf
#include <stdlib.h>     // for exit
#include <string.h>     // for bzero
#include <unistd.h>

#define PORT 6666 
#define BUFFER_SIZE 1024

int main(int argc, char *argv[])
{
    int recv_bytes = 0, send_bytes = 0;
    char recv_buf[BUFFER_SIZE] = {0};
    char send_buf[BUFFER_SIZE] = {"hello"};
    int server_socket = 0;
    //定义socket地址结构client_addr
    struct sockaddr_in client_addr;
    socklen_t length = sizeof(client_addr);
    //设置socket地址结构client_addr
    struct sockaddr_in server_addr;
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htons(INADDR_ANY);
    server_addr.sin_port = htons(PORT);
    //新建一个socket
    if((server_socket = socket(PF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("server create socket failed\n");
        return -1;
    }
    
    int opt =1;
    setsockopt(server_socket,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
    //讲server_addr地址和server_socket接口绑定
    if(bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)))
    {
        printf("server bind socket failed\n");
        return -1;
    }
    //设置最大连接数
    if(listen(server_socket, 10))
    {
        printf("server listen failed\n");
        return -1;
    }
    
    while(1)
    {
        int new_socket = 0;
        printf("waiting for client connect\n");
        //等待客户端连接
        if((new_socket = accept(server_socket, (struct sockaddr*)&client_addr, &length)) < 0)
        {
            printf("server accept socket failed\n");
            return -1;
        }
        //接收客户端数据，保存到recv_buf
        if((recv_bytes = recv(new_socket, recv_buf, sizeof(recv_buf), 0)) < 0)
        {
            printf("serve recv data failed\n");
            return -1;
        }
        
        printf("serve recv data from: %s\n", recv_buf);
        sleep(2);//休眠2s(为了显示直观，测试用)
        printf("server send data to client......");
        sleep(5);//休眠5s(为了显示直观，测试用)
        //发送数据到客户端
        if((recv_bytes = send(new_socket, send_buf, sizeof(send_buf), 0)) < 0)
        {
            printf("server send data failde\n");
            return -1;
        }
        
        printf("server send data to client: %s\n", send_buf);
        close(new_socket);//关闭new_socket
    }
        
    close(server_socket);//关闭server_socket
    
    return 0;        
}

/******client********/

#include <netinet/in.h>    // for sockaddr_in
#include <sys/types.h>    // for socket
#include <sys/socket.h>    // for socket
#include <stdio.h>        // for printf
#include <stdlib.h>        // for exit
#include <string.h>        // for bzero
#include <unistd.h>
#include <arpa/inet.h>

#define PORT 6666 
#define BUFFER_SIZE 1024


int main(int argc, char *argv[])
{
    if(argc != 3)
    {
        printf("please input the ip and the text\n");
        return -1;
    }
    int send_bytes = 0, recv_bytes = 0;
    char buf[BUFFER_SIZE] = {0};
    //设置socket的地址结构client_addr
    int client_socket;
    struct sockaddr_in client_addr, server_addr;
    bzero( &client_addr, sizeof(client_addr) );
    client_addr.sin_family = AF_INET;
    client_addr.sin_addr.s_addr = htons(INADDR_ANY);
    client_addr.sin_port = htons(0);
    //设置socket的地址结构server_addr
    bzero( &server_addr, sizeof(server_addr) );
    server_addr.sin_family = AF_INET;
    if(inet_aton(argv[1],&server_addr.sin_addr) == 0)//IP地址格式转换
    {
        printf("client server IP error\n");
        return -1;
    }
    server_addr.sin_port = htons(PORT);
    //新建一个socket
    if( (client_socket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("client create socket failed\n");
        return -1;
    }
    //将client_addr的地址和client_socket绑定
    if(bind(client_socket, (struct sockaddr*)&client_addr, sizeof(client_addr)))
    {
        printf("client bind socket failed\n");
        return -1;
    }
    printf("connect to server.........\n");
    //通过socket接口client_socket链接地址server_addr
    if(connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0)
    {
        printf("client can not connect to server: %s", argv[1]);
        return -1;
    }
    sleep(5);//休眠5s（主要为了是结果更直观）
    //通过client_socket接口，发送数据到服务器
    if((send_bytes = send(client_socket, argv[2], sizeof(argv[2]), 0)) < 0)
    {
        printf("client send data error\n");
        return -1;
    }
    printf("client send data to server: %s\n", argv[2]);
    //通过client_socket接口接收数据到buf
    if((recv_bytes = recv(client_socket, buf, sizeof(buf), 0)) < 0)
    {
        printf("client recv data from server error\n");
    }
    
    printf("client recv data from server: %s\n", buf);
    
    close(client_socket);//关闭client_socket
    
    return 0;   
    
}