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From: minow@decvax.UUCP (Martin Minow)
Newsgroups: comp.sys.atari.st
Subject: Re: FILE I/O
Message-ID: <183@decvax.UUCP>
Date: Tue, 10-Nov-87 20:05:29 EST
Article-I.D.: decvax.183
Posted: Tue Nov 10 20:05:29 1987
Date-Received: Fri, 13-Nov-87 03:57:41 EST
References: <2023@homxc.UUCP>
Reply-To: minow@decvax.UUCP (Martin Minow)
Organization: Digital Eq. Corp. - Merrimack NH.
Lines: 108
Keywords: Mark Williams C, Fseek, fseek

In article <2023@homxc.UUCP> jdn@homxc.UUCP (J.NAGY) asks about the
difference between Fseek and fseek (etc.), noting that they look
quite similar.

The "lower-case" functions match the C stdio library routines.
The "Upper-case" functions are direct calls to the operating system.
(As such, they are closer to lseek(), open(), etc.)  As noted, the
lower-case functions are generally preferable for portability.

The Upper-case functions are the only ones that can be used in a desk
accessory (they don't expand memory).  They are *much* harder to use.
As a public-service, I'm including a small open a file and read a byte
routine.  The code is made ugly as the operating system doesn't seem
to have a notion of "end of file."  (It's extracted from a longer program
and untested as such, so use it as a model only.)

Martin Minow
decvax!minow

-----
#include <osbind.h>
#include <stat.h>

#define FileBufferSize	512
typedef struct {
    int		handle;
    long	filesize;
    long	offset;
    char	*bp;
    char	*ep;
    char	buffer[FileBufferSize];
} FileInfo;

#define FileTell(fid)	((fid)->offset)

#define strchr	index			/* Brain-damaged Software Dev.	*/

FileInfo	InFile;
char		filename[64];		/* Stores file name for open	*/


typeout(infile)
char		*infile;
{
	register int		c;

	if (strchr(infile, ':') == NULL
	 && strchr(infile, '\\') == NULL) {
	    filename[0] = Dgetdrv() + 'a';
	    filename[1] = ':';
	    filename[2] = EOS;
	    Dgetpath(&filename[2], 0);	/* Must use "default" here	*/
	    strcat(filename, "\\");
	    strcat(filename, infile);
	}
	else {
	    strcpy(filename, infile);	/* User specified drive name	*/
	}
	if (FileOpen(&InFile, filename, 0) < 0) {
	    Cconws("Can't open the file\r\n");
	    Pterm(1);
	}
	while ((c = FileGetc(&InFile)) != EOF)
	    Cconout(c);
	Fclose(Infile.handle);
	Pterm(0);
}

int
FileOpen(fid, filename, mode)
register FileInfo	*fid;		/* Store stuff here		*/
char			*filename;	/* Fully-qualified file name	*/
int			mode;		/* Open mode			*/
{
	DMABUFFER	stupid;		/* Needed to get file size	*/
	int		status;

	Fsetdta(&stupid);
	if ((status = Fsfirst(filename, 0)) < 0)
	    return (status);
	fid->filesize = stupid.d_fsize;
	fid->offset = 0;
	fid->bp = fid->ep = NULL;
	fid->handle = Fopen(filename, mode);
	return (fid->handle);
}

int
FileGetc(fid)
register FileInfo	*fid;
{
	register long		readsize;
	register int		result;

	if (fid->offset >= fid->filesize)
	    return (EOF);
	while (fid->bp >= fid->ep) {
	    readsize = fid->filesize - fid->offset;
	    if (readsize > FileBufferSize)
		readsize = FileBufferSize;
	    if ((readsize = Fread(fid->handle, readsize, fid->buffer)) <= 0)
		return (EOF);
	    fid->bp = &fid->buffer[0];
	    fid->ep = &fid->buffer[readsize];
	}
	fid->offset++;
	return(*fid->bp++ & 0xFF);
}