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From: hubert@spica.ucsb.edu
Newsgroups: comp.unix.wizards
Subject: Socket datagram again.
Message-ID: <11242@hub.ucsb.edu>
Date: 15 May 91 02:21:04 GMT
Sender: news@hub.ucsb.edu
Lines: 84

Thanks to Kiartik and Oliver. I got the datagram working.

But when I tried  the following program(which could be wrong. I am a rooky.)
 I found out that if I don't add exit(0) at the end of the program. The
a.out will give me segment fault. Whay is that?



#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>

struct record
{
    int from;
    int to[10];
}

main()
{
int s1,s2,ret,fromlen;
struct sockaddr	sock1,sock2,stemp;
struct record r1,r2;

	sock1.sa_family=PF_UNIX; sock2.sa_family=PF_UNIX;
	sprintf(sock1.sa_data,"sock1"); sprintf(sock2.sa_data,"sock2");
	unlink(sock1.sa_data); unlink(sock2.sa_data);

	if ((s2=socket(PF_UNIX, SOCK_DGRAM,0)) == -1)
		perror("child socket creating error \n");

	if (bind(s2, &sock2,sizeof(sock2))==-1)
			perror("child binding eror\n");

	if ((s1=socket(PF_UNIX, SOCK_DGRAM,0)) == -1)
		perror("parent socket creating error \n");

	if (bind(s1, &sock1,sizeof(sock1))==-1)
		perror("parent binding eror\n");

	r1.from=10;
	r1.to[0]=9;

	if (sendto(s1, &r1, sizeof(struct record),0, &sock2,sizeof(sock2))==-1)
		perror("parent send error\n");

	if ( fork()==0)
	{
		printf("child birth\n");

		if (recvfrom(s2, (char *) &r2, sizeof(struct record),0,&stemp,&fromlen) == -1)
			perror("child receive error\n");
		else 
		{
			printf("child got:%d\n",r2.from);
			printf("child got:%d\n",r2.to[0]);
		}

	printf("child o.k\n");

		exit(0);
	}

	printf("parent\n");

	if (wait(&ret) ==-1)
		perror("wait error \n");

	printf("parent o.k\n");

	if (close(s1)== -1)
		perror("close fail"); 
	if (close(s2)==-1)
		perror("close s2 fail");

	exit(0);

}
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hung-Hsien Chang ( Hubert)		E-mail: hubert@cs.ucsb.edu

P.S: Hubert is not my middle name; it is easier for American friends to call me.