服务器及客户端代码小例子+对accept的理解

yyp@ubuntu:~$ netstat -anp|grep a.out
（并非所有进程都能被检测到，所有非本用户的进程信息将不会显示，如果想看到所有信息，则必须切换到 root 用户）
tcp        0      0 0.0.0.0:1234            0.0.0.0:* LISTEN      1230/a.out
tcp        0      0 10.2.1.128:44825        10.2.1.128:1234         ESTABLISHED 1231/a.out
tcp        0      0 10.2.1.128:1234         10.2.1.128:44825        ESTABLISHED 1230/a.out

accept会创建一个新的socket，所以服务器+客户端的一次连接会有三个端口，结果如上所示。

下面是client和server的源代码

#include <iostream>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
using namespace std;

int main()
{
    int fd;
    fd = socket(AF_INET, SOCK_STREAM, 0);
    if(fd ==-1)
    {
        cout<<"socket error"<<endl;
        exit(-1);
    }
    cout<<"socket ok"<<endl;

    struct sockaddr_in my_addr;
    socklen_t peer_addr_size;

    memset(&my_addr, 0, sizeof(struct sockaddr_in));

    my_addr.sin_family=AF_INET;
    my_addr.sin_port=htons(1234);
    my_addr.sin_addr.s_addr=htonl(INADDR_ANY);

    int bindFd = bind(fd, (struct sockaddr*)&my_addr, sizeof(struct sockaddr_in));
    if(bindFd==-1){
        cout<<"bind Error"<<endl;
         close(fd);
     exit(-1);
    }
    cout<<"bind ok"<<endl;
    char buffer[512];
    int liFd = listen(fd, 5);
    if(liFd==-1)
    {
        cout<<"lsten error"<<endl;
        exit(-1);
    }

    cout<<"listening"<<endl;

    while(true)
    {
        cout<<"ready to accept"<<endl;
        struct sockaddr_in peer;
        int acceptFd;
        socklen_t len=sizeof(peer);
        acceptFd = accept(fd,(struct sockaddr *)&peer, &len);
        if(acceptFd == -1)
        {
            cout<<"accept error"<<endl;
         exit(-1);
        }
        cout<<"accepted"<<endl;
        while(true){}
        write(acceptFd, "hello", sizeof("hello"));
        cout<<"write hello"<<endl;
        close(acceptFd);
    }


    close(fd);

    return 0;
}

client:

#include <iostream>
#include <stdio.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <iostream>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <strings.h>
using namespace std;

int main()
{
    int sfd = socket(AF_INET, SOCK_STREAM, 0);
    if(sfd==-1)
    {
        cout<<"socket error"<<endl;
        exit(-1);
    }

    cout<<"socket ok"<<endl;

    struct sockaddr_in server;
    bzero(&server, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_port = htons(1234);
//    server.sin_addr.s_addr = inet_addr("10.2.1.128");
    inet_pton(AF_INET, "10.2.1.128", &server.sin_addr);
    cout<<"ready to connect"<<endl;
    printf("%u\n", server.sin_addr.s_addr>>24);
    int cfd = connect(sfd, (struct sockaddr*)&server, sizeof(server));
    if(cfd==-1)
    {
        cout<<"connect error"<<endl;
        exit(-1);
    }

    cout<<"connected"<<endl;
    char buf[1000];
    while(true){}
    read(cfd,buf, 1000);
    cout<<buf<<endl;
    close(cfd);
    close(sfd);
    return 0;
}