Date: 11 Nov 87 01:05:29 GMT
Comment:  Extracted form Info-Atari16 (INFO-A16) digest number 87-411
From: decvax!minow@ucbvax.Berkeley.EDU  (Martin Minow)
Subject: Re: FILE I/O: C turorial on Upper & lower case routines for I/O
To: info-atari16@score.stanford.edu

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);