struct sockaddr
{
    unsigned short int sa_family;
    char sa_data[14];
};

struct socketaddr_in
{
    unsigned short int sin_family;
    uint16_t sin_port;
    struct in_addr sin_addr;
    unsigned char sin_zero[8];
};
struct in_addr
{
    uint32_t s_addr;
};

/* 利用socket的TCP client
此程序会连线TCP server，并将键盘输入的字符串传送给server。
TCP server使用示例请参考listen（）。
*/
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#define PORT 1234
#define SERVER_IP “127.0.0.1”
main()
{
    int s;
    struct sockaddr_in addr;
    char buffer[256];
    if((s = socket(AF_INET,SOCK_STREAM,0))<0){
        perror(“socket”);
        exit(1);
    }
    /* 填写sockaddr_in结构*/
    bzero(&addr,sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port=htons(PORT);
    addr.sin_addr.s_addr = inet_addr(SERVER_IP);
    /* 尝试连线*/
    if(connect(s,&addr,sizeof(addr))<0){
        perror(“connect”);
        exit(1);
    }
    /* 接收由server端传来的信息*/
    recv(s,buffer,sizeof(buffer),0);
    printf(“%s\n”,buffer);
    while(1){
        bzero(buffer,sizeof(buffer));
        /* 从标准输入设备取得字符串*/
        read(STDIN_FILENO,buffer,sizeof(buffer));
        /* 将字符串传给server端*/
        if(send(s,buffer,sizeof(buffer),0)<0){
            perror(“send”);
            exit(1);
        }
    }
}

#include<sys/types.h>
#include<sys/socket.h>
main()
{
    int s,optval,optlen = sizeof(int);
    if((s = socket(AF_INET,SOCK_STREAM,0))<0)
        perror(“socket”);
    getsockopt(s,SOL_SOCKET,SO_TYPE,&optval,&optlen);
    printf(“optval = %d\n”,optval);
    close(s);
}

#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<unistd.h>
#define PORT 1234
#define MAXSOCKFD 10
main()
{
    int sockfd,newsockfd,is_connected[MAXSOCKFD],fd;
    struct sockaddr_in addr;
    int addr_len = sizeof(struct sockaddr_in);
    fd_set readfds;
    char buffer[256];
    char msg[ ] =”Welcome to server!”;
    if ((sockfd = socket(AF_INET,SOCK_STREAM,0))<0){
        perror(“socket”);
        exit(1);
    }
    bzero(&addr,sizeof(addr));
    addr.sin_family =AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    if(bind(sockfd,&addr,sizeof(addr))<0){
        perror(“connect”);
        exit(1);
    }
    if(listen(sockfd,3)<0){
        perror(“listen”);
        exit(1);
    }
    for(fd=0;fd<MAXSOCKFD;fd++)
    is_connected[fd]=0;
    while(1){
        FD_ZERO(&readfds);
        FD_SET(sockfd,&readfds);
        for(fd=0;fd<MAXSOCKFD;fd++)
            if(is_connected[fd])
                FD_SET(fd,&readfds);
        if (!select(MAXSOCKFD,&readfds,NULL,NULL,NULL))
            continue;
        for (fd=0;fd<MAXSOCKFD;fd++){
            if (FD_ISSET(fd,&readfds)){
                if(sockfd = =fd){
                    if((newsockfd = accept (sockfd,&addr,&addr_len))<0)
                        perror(“accept”);
                    write(newsockfd,msg,sizeof(msg));
                    is_connected[newsockfd] = 1;
                    printf(“cnnect from %s\n”,inet_ntoa(addr.sin_addr));
                } else {
                    bzero(buffer,sizeof(buffer));
                    if(read(fd,buffer,sizeof(buffer))<=0){
                        printf(“connect closed.\n”);
                        is_connected[fd]=0;
                        close(fd);
                    }else{
                        printf(“%s”,buffer);
                    }
                }
            }
        }
    }
}

/*利用socket的UDP client
此程序会连线UDP server，并将键盘输入的字符串传给server。
UDP server 使用示例请参考sendto（）。
*/
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/typs.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#define PORT 2345
#define SERVER_IP “127.0.0.1”
main()
{
    int s,len;
    struct sockaddr_in addr;
    int addr_len =sizeof(struct sockaddr_in);
    char buffer[256];
    /* 建立socket*/
    if((s = socket(AF_INET,SOCK_DGRAM,0))<0){
        perror(“socket”);
        exit(1);
    }
    /* 填写sockaddr_in*/
    bzero(&addr,sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = inet_addr(SERVER_IP);
    while(1){
        bzero(buffer,sizeof(buffer));
        /* 从标准输入设备取得字符串*/
        len =read(STDIN_FILENO,buffer,sizeof(buffer));
        /* 将字符串传送给server端*/
        sendto(s,buffer,len,0,&addr,addr_len);
        /* 接收server端返回的字符串*/
        len = recvfrom(s,buffer,sizeof(buffer),0,&addr,&addr_len);
        printf(“receive: %s”,buffer);
    }
}

struct msghdr
{
    void *msg_name; /*Address to send to /receive from . */
    socklen_t msg_namelen; /* Length of addres data */
    strcut iovec * msg_iov; /* Vector of data to send/receive into */
    size_t msg_iovlen; /* Number of elements in the vector */
    void * msg_control; /* Ancillary dat */
    size_t msg_controllen; /* Ancillary data buffer length */
    int msg_flags; /* Flags on received message */
};

#include < sys/types.h >
#include < sys/socket.h >
# include <netinet.in.h>
#include <arpa.inet.h>
#define PORT 2345 /*使用的port*/
main(){
    int sockfd,len;
    struct sockaddr_in addr;
    char buffer[256];
    /*建立socket*/
    if(sockfd=socket (AF_INET,SOCK_DGRAM,0))<0){
        perror (“socket”);
        exit(1);
    }
    /*填写sockaddr_in 结构*/
    bzero ( &addr, sizeof(addr) );
    addr.sin_family=AF_INET;
    addr.sin_port=htons(PORT);
    addr.sin_addr=hton1(INADDR_ANY) ;
    if (bind(sockfd, &addr, sizeof(addr))<0){
        perror(“connect”);
        exit(1);
    }
    while(1){
        bezro(buffer,sizeof(buffer));
        len = recvfrom(socket,buffer,sizeof(buffer), 0 , &addr &addr_len);
        /*显示client端的网络地址*/
        printf(“receive from %s\n “ , inet_ntoa( addr.sin_addr));
        /*将字串返回给client端*/
        sendto(sockfd,buffer,len,0,&addr,addr_len);”
    }
}