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From:	cbutler AT bnr DOT ca (Chris Butler)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Strange bug using 'fwrite'
Date:	11 Dec 1995 04:20:54 GMT
Organization:	Bell-Northern Research Ltd.
Lines:	65
Distribution:	na
Nntp-Posting-Host:	bmerha40.bnr.ca
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi folks,

   I was coding away this weekend when the following bug
stopped me dead.

   I'm using fwrite to write bytes to a file.  Here's a
program sample:
--------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main() {
   FILE *f2;
   char vers_update[5];
   int rec_count = 1;
   short hlength = 2, reclength = 3;
   char extra_bytes[25];
   int i;

   for (i = 0; i < 20; i++)
      extra_bytes[i] = i + 5;

   strcpy(vers_update, "abcd");
   f2 = fopen("out.2", "w");
   if (f2 == 0) {
      printf("Couldn't open '%s' for writing... aborting.\n", "out.2");
      exit(1);
   }

   fwrite(vers_update, 1, 4, f2);
   fwrite(&rec_count, 1, 4, f2);
   fwrite(&hlength, 1, 2, f2);
   fwrite(&reclength, 1, 2, f2);
   fwrite(extra_bytes, 1, 20, f2);
   fclose(f2); 
}
---------------------------- 
Please, no smart remarks about coding style - I cut & pasted this
together.  Anyway, when I compile and run this on my PC, I get the 
following hex dump from the file "out.2":

61 62 63 64 01 00 00 00  02 00 03 00 05 06 07 08
09 0d 0a 0b 0c 0d 0e 0f  10 11 12 13 14 15 16 17
18

....for a grand total of 33 bytes, where I was only expecting 32.
Note also the '0d', second byte on the 2nd line.  Anyone have
any ideas where it came from?  The program works as I'd expect
it to on UNIX.  I haven't tried rewriting the above to use
file descriptors instead of file pointers, so I'm not sure
what happens there.

   Also, I messed around with the initialization of the 'extra_bytes'
in other tests - the '0d' always seems to follow the '09'.

System info:  486 80 MHz CPU, 4 megs RAM, gcc v2.6.3 .

Any info would be appreciated - thanks.

-Chris

-- 
Chris Butler aka cbutler AT bnr DOT ca -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
         All standard disclaimers apply.  Have an adequate day.

- Raw text -