网络编程（三）---数据报套接字

1、sendto函数向数据报套接字发送数据包；

     int sendto(int sockfd, void* buffer, size_t size, int flags, struct sockaddr* to, size_t addrlen);

2、recvfrom函数从数据报套接字读数据包，同时报告该包从何而来；

    int recvfrom(int sockfd, void * buffer, size_t size, int flags, struct sockaddr * to, size_t * addrlen);

3、流程：

 

4、例子：

(1) DgramSocketClient.c: 数据包通信客户机程序

/*
 * DgramSocketClient.c
 *
 *  Created on: Sep 1, 2013
 *      Author: root
 */
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <unistd.h>

#define MAXMSG 512

int main(){
    int sockfd, n;
    char recvbuff[MAXMSG], sndbuff[MAXMSG];
    struct sockaddr_in servaddr;
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sockfd < 0){
        printf("Socket created failed.
");
        return -1;
    }
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(6666);
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    while(fgets(sndbuff, MAXMSG, stdin) != NULL){
        if(sendto(sockfd, sndbuff, sizeof(sndbuff), 0, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0){
            printf("client sending error.
");
            return -1;
        }
        if((n = recvfrom(sockfd, recvbuff, MAXMSG, 0, NULL, NULL)) < 0){
            printf("(client) receiving error.
");
            return -1;
        }
        recvbuff[n] = 0;
        printf("Client received message: %s", recvbuff);
    }
    close(sockfd);
    return 0;
}

(2) DgramSocketServer.c: 数据报通信服务器程序。

/*
 * DgramSocketServer.c
 *
 *  Created on: Sep 1, 2013
 *      Author: root
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#define MAXMSG 1024

int main(){
    int sockfd, size, nbytes;
    struct sockaddr_in addr;
    char message[MAXMSG];
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if(sockfd < 0){
        printf("Socket created failed.
");
        return -1;
    }
    bzero(&addr, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(6666);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    if(bind(sockfd, (struct sockaddr*)&addr, sizeof(addr)) < 0){
        printf("bind failed.
");
        return -1;
    }
    printf("listening...
");
    while(1){
        size = sizeof(addr);
        nbytes = recvfrom(sockfd, message, MAXMSG, 0, (struct sockaddr*)&addr, &size);
        if(nbytes < 0){
            printf("recvfrom (server) failed.
");
            return -1;
        }
        printf("Server got message: %s
", message);
        nbytes = sendto(sockfd, message, nbytes,0, (struct sockaddr*)&addr, size);
        if(nbytes < 0){
            printf("sendto(server) failed.
");
            return -1;
        }
    }
}

 启动服务器程序，然后启动客户端程序，输入信息回车给服务器发送消息；然后启动另外一个客户端，输入信息回车也给服务器发送消息。从服务器程序的输出结果可以看出，它收到了这两个客户发来的消息，并且接收消息的顺序是数据报到达的顺序。具体运行结果如下：