UDP的内部通讯纠结-

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//cliend 端

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

typedef struct sockaddr SA;
#define N 64

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_un servaddr, myaddr;
    char buf[N] = {0};
    ssize_t n;

    if ((sockfd = socket(PF_UNIX, SOCK_DGRAM, 0)) == -1)
    {
        perror("socket");
        exit(-1);
    }

    bzero(&myaddr, sizeof(myaddr));
    myaddr.sun_family = PF_UNIX;
    strcpy(myaddr.sun_path, "clientsocket");

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sun_family = PF_UNIX;
    strcpy(servaddr.sun_path, "serversocket");

/***********************很纠结的部分为什么要绑定一个地址*****？？？？？************************/

    if (bind(sockfd, (SA *)&myaddr, sizeof(myaddr)) == -1)
    {
        perror("bind");
        exit(-1);
    }

    while (1)
    {
        fgets(buf, N, stdin);
        buf[strlen(buf)-1] = 0;

        sendto(sockfd, buf, strlen(buf), 0, (SA *)&servaddr, sizeof(servaddr));

        bzero(buf, sizeof(buf));
        n = recvfrom(sockfd, buf, N, 0, NULL, NULL);
        buf[n] = 0;

printf("%s\n", buf);
}

close(sockfd);

exit(0);
}

//server端

typedef struct sockaddr SA;
#define N 64

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_un myaddr, peeraddr;
    socklen_t len;
    char buf[N] = {0};
    ssize_t n;

    if ((sockfd = socket(PF_UNIX, SOCK_DGRAM, 0)) == -1)
    {
        perror("socket");
        exit(-1);
    }

    bzero(&myaddr, sizeof(myaddr));
    myaddr.sun_family = PF_UNIX;
    strcpy(myaddr.sun_path, "serversocket");

    unlink("serversocket");
    if (bind(sockfd,(struct sockaddr *)&myaddr, sizeof(myaddr)) == -1)
    {
        perror("bind");
        exit(-1);
    }

bzero(&peeraddr, sizeof(peeraddr));
len = sizeof(peeraddr);

    while (1)
    {
        bzero(buf, sizeof(buf));
        n = recvfrom(sockfd, buf, N, 0, (SA *)&peeraddr, &len);
        buf[n] = 0;

        printf("from %s:%s\n", peeraddr.sun_path, buf);
        sendto(sockfd, buf, strlen(buf), 0, (SA *)&peeraddr, sizeof(peeraddr));
    }

exit(0);
}