#include <stdio .h>
#include < stdlib .h>
#include < errno .h>
#include < string .h>
#include < sys /types.h>
#include < netinet /in.h>
#include < sys /socket.h>
#include < sys /wait.h>
 
#define SERVPORT 3333 
#define BACKLOG 10
#define MAXSIZE 1024
 
int main() {
    int sockfd,client_fd;
    struct sockaddr_in my_addr;
    struct sockaddr_in remote_addr;
    //创建套接字
    if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1) {
        perror("socket create failed!");
        exit(1);
    }
 
    //绑定端口地址
    my_addr.sin_family      = AF_INET;
    my_addr.sin_port        = htons(SERVPORT);
    my_addr.sin_addr.s_addr = INADDR_ANY;
    bzero(&(my_addr.sin_zero),8);
    if (bind(sockfd, (struct sockaddr*)&my_addr, sizeof(struct sockaddr)) == -1) {
        perror("bind error!");
        exit(1);
    }
 
    //监听端口
    if (listen(sockfd, BACKLOG) == -1) {
        perror("listen error");
        exit(1); 
    }
 
    while (1) {
        int sin_size = sizeof(struct sockaddr_in);    
        if ((client_fd = accept(sockfd, (struct sockaddr*)&remote_addr,&sin_size)) == -1) {
            perror("accept error!");
            continue;
        }
        printf("Received a connection from %s\n", (char*)inet_ntoa(remote_addr.sin_addr));
 
       //子进程段
        if (!fork()) {
            //接受client发送的请示信息
            int rval;
            char buf[MAXSIZE];   
            if ((rval = read(client_fd, buf, MAXSIZE)) < 0) {
                perror("reading stream error!");
                continue;
            }
            printf("%s\n",buf);
 
            //向client发送信息
            char* msg = "Hello,Mr hqlong, you are connected!\n";
            if (send(client_fd, msg, strlen(msg), 0) == -1) perror("send error!");
            close(client_fd);
            exit(0);
        } 
        close(client_fd);
    }
    return 0;
}

hqlong@ubuntu:~$ gcc server.c -o server
hqlong@ubuntu:~$./server &

hqlong@ubuntu:~/t$ netstat -nl | grep 3333
tcp        0      0 0.0.0.0:3333            0.0.0.0:*               LISTEN

hqlong@ubuntu:~$ telnet 127.0.0.1 3333
Trying 127.0.0.1...
Received a connection from 127.0.0.1
Connected to 127.0.0.1.
Escape character is '^]'.
test
test
 
Hello,Mr hqlong, you are connected!
Connection closed by foreign host.

#include < stdio .h>
#include < stdlib .h>
#include < errno .h>
#include < string .h>
#include < sys /types.h>
#include < netinet /in.h>
#include < sys /socket.h>
#include < sys /wait.h>
 
#define SERVPORT 3333
#define MAXDATASIZE 100
#define SERVER_IP "127.0.0.1"
#define DATA  "this is a client message"
 
int main(int argc, char* argv[]) {
    int sockfd, recvbytes;
    char buf[MAXDATASIZE];
    struct hostent *host;
    struct sockaddr_in serv_addr;
 
    if (( sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket error!");
        exit(1);
    }
    bzero(&serv_addr,sizeof(serv_addr));
    serv_addr.sin_family    = AF_INET;
    serv_addr.sin_port      = htons(SERVPORT);
    serv_addr.sin_addr.s_addr= inet_addr(SERVER_IP);
 
    if (connect(sockfd, (struct sockaddr *)&serv_addr,sizeof(struct sockaddr)) == -1) {
        perror("connect error!");
        exit(1);
    }
 
    write(sockfd,DATA, sizeof(DATA));
   if ((recvbytes = recv(sockfd, buf, MAXDATASIZE,0)) == -1) {
        perror("recv error!");
        exit(1);
    }
 
    buf[recvbytes] = '\0';
    printf("Received: %s",buf);
    close(sockfd);
    return 0;
}

hqlong@ubuntu:~$ gcc client.c -o client
hqlong@ubuntu:~$ ./client
Received a connection from 127.0.0.1
Hello,Mr hqlong, you are connected!
Connection closed by foreign host.