Subject: Re: Lseek'ing backwards with SEEK_CUR?
To: None <>
From: Charles M. Hannum <>
List: current-users
Date: 12/14/1994 03:45:14
	   Is lseek'ing backwards with SEEK_CUR supported, or expected to work?

	   I have a program that writes out records to a file, sometimes needing
	   to insert them in the middle of the file.  Invariably, this program
	   will close the file at some point, resulting in a *HUGE* file that's
	   backfiled with zeros.

	   The program does this seeking about like this:

		   lseek(fd, - RECSIZE, SEEK_CUR)

It sounds like you don't have a prototype (or have an incorrect one)
in scope, so the offset is being passed as 32 bits.  The second
argument needs to be `off_t'.

	   *EITHER* way, inserting printf's that indicate current file positions
	   [by means of printf("%qd", lseek(fd, 0, SEEK_CUR))] indicate that the
	   file pointer is in the correct place.

Again, if you don't have a prototype, the return value will be taken
as 32 bits, plus whatever 32 bits of junk happens to be on the stack
above it.