linux下udp的通信例子

 UDP客户端在建立了插口后会直接用sendto函数发送数据，还隐含了一个操作，
那就是在发送数据之前，UDP会首先为该插口选择一个独立的UDP端口（在1024
-5000之间），将该插口置为已绑定状态。如果一个UDP客户端在建立了插口后
首先用bind函数指明了本地地址/端口，也是可以的，这样可以强迫UDP使用指
定的端口发送数据。（事实上，UDP无所谓服务器和客户端，这里的界限已经模
糊了。）

//======================================================

//服务端

#include
#include
#include
#include
#include
#include


#define MAXLINE 80
#define SERV_PORT 502


void do_echo(int sockfd, struct sockaddr *pcliaddr, socklen_t clilen)
{
    int n;
    socklen_t len;
    char mesg[MAXLINE];


    for(;;)
    {
        len = clilen;
        /* waiting for receive data */
        n = recvfrom(sockfd, mesg, MAXLINE, 0, pcliaddr, &len);
        mesg[n-1]=0;
        printf("recvfrom data:%s\n",mesg);
        /* sent data back to client */
        sendto(sockfd, mesg, n, 0, pcliaddr, len);
    }
}


int main(void)
{
    int sockfd;
    struct sockaddr_in servaddr, cliaddr;


    sockfd = socket(AF_INET, SOCK_DGRAM, 0); /* create a socket */


    /* init servaddr */
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);


    /* bind address and port to socket */
    if(bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
    {
        perror("bind error");
        exit(1);
    }
    printf("UPD servese is bind success and do_echo now\n");
    do_echo(sockfd, (struct sockaddr *)&cliaddr, sizeof(cliaddr));


    return 0;
}

//=============================================

//客户端1 使用本地固定的端口

#include
#include
#include
#include
#include
#include
#include
#include

#define MAXLINE 80
#define SERV_PORT 8888

void do_cli(FILE *fp, int sockfd, struct sockaddr *pservaddr, socklen_t servlen)
{
    int n;
    char sendline[MAXLINE], recvline[MAXLINE + 1];

    /* connect to server */
    if(connect(sockfd, (struct sockaddr *)pservaddr, servlen) == -1)
    {
        perror("connect error");
        exit(1);
    }

    printf("Please input your str want to send:\n");
    while(fgets(sendline, MAXLINE, fp) != NULL)
    {
        /* read a line and send to server */
        write(sockfd, sendline, strlen(sendline));
        /* receive data from server */
        n = read(sockfd, recvline, MAXLINE);
        if(n == -1)
        {
            perror("read error");
            exit(1);
        }
        recvline[n] = 0; /* terminate string */
        printf("receive str:\n");
        fputs(recvline, stdout);
        printf("\n==================================\n");
        printf("Please input your str want to send:\n");
    }
}

int main(int argc, char **argv)
{
    int sockfd;
    struct sockaddr_in servaddr;

    /* check args */
    if(argc != 2)
    {
        printf("usage: udpclient \n");
        exit(1);
    }

    /* init servaddr */
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(SERV_PORT);
    if(inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
    {
        printf("[%s] is not a valid IPaddress\n", argv[1]);
        exit(1);
    }

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    printf("cli is ready,now do funtion do_cli! \n", argv[1]);
    do_cli(stdin, sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));


    return 0;
}

//==================================

//客户端2 代码 使用随机端口
//http://haibor1x.blog.163.com/blog/static/763407200751052458572/
#include
#include
#include
#include
#include
#include
#include
#include

#define SERV_PORT 502
#define MAXLINE 80

void do_cli(FILE *fp, int sockfd, sockaddr_in toAddr)
{
    int n;
    struct sockaddr_in fromAddr;
    char sendline[MAXLINE], recvline[MAXLINE + 1];

    printf("Please input your str want to send:\n");
    while(fgets(sendline, MAXLINE, fp) != NULL)
    {
        /* read a line and send to server */
        //write(sockfd, sendline, strlen(sendline));
        if(sendto(sockfd,sendline,strlen(sendline),0,
                  (struct sockaddr*)&toAddr,sizeof(toAddr)) !=
                strlen(sendline))
        {
            printf("sendto() 函数使用失败了.\r\n");
            close(sockfd);
            exit(1);
        }


        printf("wait for data ...\n");
        /* receive data from server */
        //n = read(sockfd, recvline, MAXLINE);


        unsigned int fromLen = sizeof(fromAddr);
        if(recvfrom(sockfd,recvline,MAXLINE,0,
                        (struct sockaddr*)&fromAddr,&fromLen)<0)
        {
            printf(" ()recvfrom()函数使用失败了.\r\n");
            close(sockfd);
            exit(1);
        }
        else{
            printf("get nothing data ...\n");
        }
        recvline[strlen(sendline)-1] = 0;
        printf("receive str:\n");
        fputs(recvline, stdout);
        printf("\n==================================\n");
        printf("Please input your str want to send:\n");
    }
}


int main(int argc, char *argv[])
{
    int sock;
    //sendto中使用的对方地址
    struct sockaddr_in toAddr;
    //在recvfrom中使用的对方主机地址
    struct sockaddr_in fromAddr;

    sock = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);

    if(sock < 0)
    {
        printf(" 创建套接字失败了.\r\n");
        exit(1);
    }

    memset(&toAddr,0,sizeof(toAddr));
    toAddr.sin_family=AF_INET;
    toAddr.sin_addr.s_addr=inet_addr("192.168.0.110");
    toAddr.sin_port = htons(SERV_PORT);

    do_cli(stdin, sock, toAddr);

    close(sock);
    return 0;
}