Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!bria!mike
From: mike@bria.AIX (Mike Stefanik/78125)
Newsgroups: comp.lang.c
Subject: Re: Structure hopping
Message-ID: <315@bria.AIX>
Date: 4 Jan 91 05:19:00 GMT
References: <949@tfsg.UUCP>
Reply-To: mike@bria.UUCP (Michael Stefanik)
Organization: Briareus Corporation, Los Angeles, CA
Lines: 60

In article <949@tfsg.UUCP> mark@tfsg.UUCP (Mark Crafts) writes:
>Forgive my ignorance, but is there a quick 'n' simple way to say,
>dump a structure to a file (or whatever) using pointers, if we
>know that the structure only consists of, (for example) chars?
[proceeds to describe a structure]

Actually, there is a very simple way to do this; consider the following:

struct foo {
		int	anumber;
		long	along;
		char	somestring[64];
		float	areal;
		char	anotherstring[128];
		} bar;

funwithfoo()
{
int	fd;

	/* here we open a file named "datafile"; this usage opens the
	   file for reading and writing, appending to the file if it
	   exits, otherwise creating it */

	if ( (fd = open("datafile",O_RDWR|O_CREAT|O_APPEND,0644)) == -1 ) {
		fprintf(stderr,"Bad karma dude!  I cannot create datafile\n");
		exit(1);
		}

	/* here we write the contents of 'bar' out to the file we just opened;
	   note the & operator that provides us with the address of 'bar',
	   which is sizeof(struct foo) bytes */

	write(fd,&bar,sizeof(struct foo));

	/* here we close our file */

	close(fd);

	/* now, let's reopen the file, and sequentially read through the
	   records that we have written (perhaps in the past?) */

	if ( (fd = open("datafile",O_RDONLY)) == -1 ) {
		fprintf(stderr,"Bad karma dude!  Datafile doesn't exist!\n");
		exit(1);
		}

	while ( read(fd,&bar,sizeof(struct foo)) == sizeof(struct foo) ) {
		/* here we display the guts of struct foo */
		};

	close(fd);
}

Forgive any typos, etc.  Hopefully you'll get the picture.

-----------------------------------------------------------------------------
Michael Stefanik, Systems Engineer (JOAT), Briareus Corporation
UUCP: ...!uunet!bria!mike
"If it was hard to code, it should be harder to use!"