connect()在UDP连接中的应用一例

服务器：

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


#define N 256

typedef struct sockaddr SA;

int main(int argc, char* argv[])
{
    int sockfd;
    struct sockaddr_in my_addr, peer_addr;
    socklen_t peerlen = sizeof(peer_addr);
    char buffer[N];

    if((sockfd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("fail to socket");
        exit(-1);
    }

   my_addr.sin_family = PF_INET;
   my_addr.sin_port = htons(atoi(argv[2]));
   my_addr.sin_addr.s_addr = inet_addr(argv[1]);

   if(bind(sockfd, (SA *)&my_addr, sizeof(my_addr)) < 0)
   {
       perror("fail to bind");
       exit(-1);
   }

    while(1)
    {

        recvfrom(sockfd, buffer, N, 0,(SA*)&peer_addr, &peerlen);
        printf("client: [%s : %d], %s",inet_ntoa(peer_addr.sin_addr),ntohs(peer_addr.sin_port),buffer);
        sendto(sockfd, buffer, N, 0, (SA *)&peer_addr, sizeof(peer_addr));
        bzero(buffer, N);
    }


    return 0;
}

客户端：

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


#define N 256

typedef struct sockaddr SA;

int main(void)
{
    int sockfd;
    struct sockaddr_in my_addr;
    char buffer[N];

    if((sockfd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("fail to socket");
        exit(-1);
    }



    while(1)
    {

        bzero(buffer, N);
        printf("exit? Y/N");
        fgets(buffer, N, stdin);
        if(strncmp(buffer, "Y", 1) == 0)
        {
            break;
        }
        else
        {
            bzero(&my_addr,sizeof(my_addr));
            my_addr.sin_family = PF_INET;

            printf("please input server's ip > ");
            fgets(buffer, N, stdin);
            buffer[strlen(buffer) -1] = '\0';
            my_addr.sin_addr.s_addr = inet_addr(buffer);

            printf("please input server's port > ");
            fgets(buffer, N, stdin);
            buffer[strlen(buffer) -1] = '\0';
            my_addr.sin_port = htons(atoi(buffer));

            connect(sockfd, (SA *)&my_addr, sizeof(my_addr));
            while(1)
            {
                fgets(buffer, N, stdin);
                if(strncmp(buffer, "quit", 4) == 0)
                {
                    break;
                }

                send(sockfd, buffer, N, 0);
                bzero(buffer, N);
                recv(sockfd, buffer, N, 0);
                printf("receive from the server > %s",buffer);
            }
        }
    }

    close(sockfd);
    return 0;
}

运行：

运行了两个服务器：

客户端：

这样，通过在UDP中使用connect()，省去了每次都输入服务器地址的操作，而且一个在这种情况下，一个套接字在不关闭的情况下可以实现多次调用connect()。