A UDP Demo

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

#define UDP_TEST_PORT       50001

int main(int argC, char* arg[])
{
    struct sockaddr_in addr;
    int sockfd, len = 0;
    int addr_len = sizeof(struct sockaddr_in);
    char buffer[256];

    /* 建立socket，注意必须是SOCK_DGRAM */
    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(UDP_TEST_PORT);
    addr.sin_addr.s_addr = htonl(INADDR_ANY) ;// 接收任意IP发来的数据

    /* 绑定socket */
    if (bind(sockfd, (struct sockaddr *)&addr, sizeof(addr))<0) {
        perror("connect");
        exit(1);
    }

    while(1) {
        bzero(buffer, sizeof(buffer));
        len = recvfrom(sockfd, buffer, sizeof(buffer), 0,
                       (struct sockaddr *)&addr ,&addr_len);
        /* 显示client端的网络地址和收到的字符串消息 */
        printf("Received a string from client %s, string is: %s\n",
               inet_ntoa(addr.sin_addr), buffer);
        /* 将收到的字符串消息返回给client端 */
        sendto(sockfd,buffer, len, 0, (struct sockaddr *)&addr, addr_len);
    }

    return 0;
}

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

#define UDP_TEST_PORT       50001
#define UDP_SERVER_IP           "127.0.0.1"

int main(int argC, char* arg[])
{
    struct sockaddr_in addr;
    int sockfd, len = 0;
    int addr_len = sizeof(struct sockaddr_in);
    char buffer[256];

    /* 建立socket，注意必须是SOCK_DGRAM */
    if ((sockfd = 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(UDP_TEST_PORT);
    addr.sin_addr.s_addr = inet_addr(UDP_SERVER_IP);

    while(1) {
        bzero(buffer, sizeof(buffer));

        printf("Please enter a string to send to server: \n");

        /* 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(sockfd, buffer, len, 0, (struct sockaddr *)&addr, addr_len);

        /* 接收server端返回的字符串*/
        len = recvfrom(sockfd, buffer, sizeof(buffer), 0,
                       (struct sockaddr *)&addr, &addr_len);
        printf("Receive from server: %s\n", buffer);
    }

    return 0;
}