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Subject: lseek + read = ENOENT
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From: Sam Steingold <sds AT gnu DOT org>
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Date: Thu, 19 Jan 2006 16:10:25 -0500
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I cannot read the last 4-byte word in a file using lseek + read:

/* file "foo" exists and is large enough - say, 4 MB */
  int fd = open("foo",O_RDONLY|O_BINARY);
  uint32 data;
/* this succeeds and correctly returns the size of file "foo" minus 4 */
  lseek(fd,-sizeof(data),SEEK_END);
/* this returns 0 -- instead of the expected 4 -- and sets errno to ENOENT */
  read(fd,&data,sizeof(data));

if I run this under gdb and type
  lseek(fd,-sizeof(data),SEEK_END);
  read(fd,&data,sizeof(data));
several times, eventually read() starts to return 4 and set data to the
value I actually wrote into "foo" last.

I observe this on linux, cygwin and solaris -- what am I doing wrong?

Thanks!

-- 
Sam Steingold (http://www.podval.org/~sds) running w2k
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