From:	CRDGW2::CRDGW2::MRGATE::"SMTP::CRVAX.SRI.COM::RELAY-INFO-VAX" 30-OCT-1990 05:25:07.23
To:	MRGATE::"ARISIA::EVERHART"
CC:	
Subj:	Re: fflush() and open files

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Date: 30 Oct 90 03:23:24 GMT
From: usc!samsung!umich!sharkey!bnlux0!bnlls1!rivers@ucsd.edu  (Mark Rivers)
Organization: Brookhaven National Labs(NSLS)
Subject: Re: fflush() and open files
Message-Id: <2269@bnlux0.bnl.gov>
References: <278@talarian.UUCP>
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This routine shows how to do file sharing under VMS with VAXC. One
process can write to the file while others simultaneuously read from it.
The important lines below are the creat() and open() function calls.
I have not worried about fflush(), since I don't care if I am one or 2
lines behind when I read the file. Experiment to see if it is
necessary.

#include <stdio.h>
#include <file.h>
#include "image_header.h"
#include "image_buffer.h"
#define PMODE 0644     /* Default protection on UNIX systems = RW for 
			owner, R for everyone else */

/* This buffer is defined in write_image_record */
extern char scratch_buffer[MAX_REC_LEN];

open_image_file(file_id, file_name, file_name_len, new_file)

/* This routine opens an existing or new BSIF image file. It is system
dependent and has conditional compilation for UNIX and VMS.

   13-DEC-1988  Changed VMS version to allow shared access to files, so one
program can be writing to a file while other programs read it. */

int *file_id;
char *file_name;
int *file_name_len;
int *new_file;

{

	char max_rec_size[20];

/*	Copy the file name to the scratch buffer and terminate with a NULL
	since this may be being called from FORTRAN, which doesn't null 
	terminate strings */
	strncpy(scratch_buffer, file_name, *file_name_len);
	scratch_buffer[*file_name_len] = 0;

/*	Format maximum record length */
	sprintf(max_rec_size, "mrs=%d", MAX_REC_LEN);
	if (*new_file) {
#ifdef VMS
	   *file_id = creat(scratch_buffer, 0, "rfm=var", max_rec_size,
					"ctx=rec", "shr=get");
#endif
#ifdef unix
	   *file_id = creat(scratch_buffer, PMODE);
#endif
	}
	else {
#ifdef VMS
	   *file_id = open(scratch_buffer, O_RDONLY, 0, 
				"shr=put,get,del,upd", "ctx=rec");
#endif
#ifdef unix
	   *file_id = open(scratch_buffer, 0);
#endif
	}

	if (*file_id == -1) return (0);
	return(1);
}


Mark Rivers                              (516) 282-7708 or 5626
Building 815                             rivers@bnlx26.nsls.bnl.gov (Internet) 
Brookhaven National Laboratory           rivers@bnl (Bitnet)                   
Upton, NY 11973                          BNLX26::RIVERS  (Physnet)