linux 套接字编程入门--Hello World

　　下述代码是linux套接字编程的入门代码.分为服务端和客户端源码.

　　服务端代码的主要流程是绑定ip地址和端口号建立套接字,等待客户端发起访问.接受客户端请求之后,向客户端发送字符串"hello world",关闭套接字,结束程序.

　　客户端代码的主要流程是向服务端对应的套接字发起请求,读取服务端发送的数据,并且打印出来.

　　代码已经详细注释,更多细节不再赘述.

server.cpp

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

int main(){
    //创建套接字
    /*
     * AF_INET is an address family that is used to designate
     * the type of addresses that your socket can communicate
     * with (in this case, Internet Protocol v4 addresses).
     * When you create a socket, you have to specify its address family,
     * and then you can only use addresses of that type with the socket.
     * The Linux kernel, for example, supports 29 other address families
     * such as UNIX (AF_UNIX) sockets and IPX (AF_IPX), and also communications with IRDA
     * and Bluetooth 
     * (AF_IRDA and AF_BLUETOOTH, but it is doubtful you'll use these at such a low level).
     * For the most part, sticking with AF_INET for socket programming over
     * a network is the safest option.
     * There is also AF_INET6 for Internet Protocol v6 addresses
     */
    /*
     * SOCK_STREAM
     * Provides sequenced, reliable, two-way, connection-
     * based byte streams.  An out-of-band data transmission
     * mechanism may be supported.
     */
    //IPPROTO_TCP 采用TCP协议
    int serv_sock =socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
    //将套接字和IP 端口号进行绑定
    struct sockaddr_in serv_addr;
    //初始化结构体serv_addr
    memset(&serv_addr,0,sizeof(serv_addr));
    //使用ipv4地址
    serv_addr.sin_family=AF_INET;
    //设置ip地址
    serv_addr.sin_addr.s_addr=inet_addr("127.0.0.1");
    //设置端口号
    serv_addr.sin_port =htons(2896);
    //将套接字和结构体进行绑定 结构体中存储了套接字的协议 端口号  以及ip地址
    bind(serv_sock,(struct sockaddr*)&serv_addr,sizeof(serv_addr));
    //进入监听状态,等待用户发起请求
    //进入被动监听状态,套接字一直处于睡眠状态,直至客户端发起请求才会被重新唤醒
    listen(serv_sock,20);
    //客户端请求对应的套接字结构体
    struct sockaddr_in client_addr;
    //客户端请求套接字结构体的大小
    socklen_t  client_addr_size =sizeof(client_addr);
    //用于接受客户端的请求
    int client_sock =accept(serv_sock,(struct sockaddr *)&client_addr,&client_addr_size);
    char str[]="hello world";
    //向客户端发送数据
    //向客户端套接字中写入数据
    write(client_sock,str,sizeof(str));
    //关闭套接字
    close(client_sock);
    close(serv_sock);
    return 0;
}

client.cpp

#include<stdio.h>
#include<cstring>
#include<stdlib.h>
#include<unistd.h>
#include <arpa/inet.h>
#include<sys/socket.h>
int main(){
    /*
     * This constant has the value 0.
     * It's actually an automatic choice depending on socket type and family.
     * If you use it, and if the socket type is SOCK_STREAM and the family is AF_INET,
     * then the protocol will automatically be TCP (exactly the same as if you'd used IPPROTO_TCP).
     * Buf if you use IPPROTO_IP together with AF_INET and SOCK_RAW, you will have an error,
     * because the kernel cannot choose a protocol automatically in this case.
     */
    int sock =socket(AF_INET,SOCK_STREAM,IPPROTO_IP);

    struct sockaddr_in serv_addr;
    memset(&serv_addr,0,sizeof(serv_addr));
    serv_addr.sin_family=AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.sin_port= htons(2896);
    //通过connect函数向客户端发起请求,服务器的套接字信息存储在结构体serv_addr中
    connect(sock,(struct sockaddr*)&serv_addr,sizeof(serv_addr));

    char buffer[40];
    //通过read从套接字中读取数据
    read(sock,buffer,sizeof(buffer)-1);

    printf("message from server: %s
",buffer);
    //关闭套接字
    close(sock);
    return 0;


}

参考:

1. stack_overflow 
2. man7
3. c语言中文网