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RedHat 9 (Linux i386) - man page for lseek (redhat section 2)

LSEEK(2)				   System calls 				 LSEEK(2)

NAME
       lseek - reposition read/write file offset

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

       off_t lseek(int fildes, off_t offset, int whence);

DESCRIPTION
       The  lseek  function  repositions the offset of the file descriptor fildes to the argument
       offset according to the directive whence as follows:

       SEEK_SET
	      The offset is set to offset bytes.

       SEEK_CUR
	      The offset is set to its current location plus offset bytes.

       SEEK_END
	      The offset is set to the size of the file plus offset bytes.

       The lseek function allows the file offset to be set beyond the end of the existing end-of-
       file of the file.  If data is later written at this point, subsequent reads of the data in
       the gap return bytes of zeros (until data is actually written into the gap).

RETURN VALUE
       Upon successful completion, lseek returns the resulting offset  location  as  measured  in
       bytes  from  the  beginning  of the file.  Otherwise, a value of (off_t)-1 is returned and
       errno is set to indicate the error.

ERRORS
       EBADF  Fildes is not an open file descriptor.

       ESPIPE Fildes is associated with a pipe, socket, or FIFO.

       EINVAL Whence is not a proper value.

CONFORMING TO
       SVr4, POSIX, BSD 4.3

RESTRICTIONS
       Some devices are incapable of seeking and POSIX does not specify which devices  must  sup-
       port it.

       Linux  specific	restrictions:  using lseek on a tty device returns ESPIPE.  Other systems
       return the number of written characters, using SEEK_SET to set the counter.  Some devices,
       e.g.  /dev/null	do  not cause the error ESPIPE, but return a pointer which value is unde-
       fined.

NOTES
       This document's use of whence is incorrect English, but maintained for historical reasons.

       When converting old code, substitute values for whence with the following macros:

	old	  new
       0	SEEK_SET
       1	SEEK_CUR
       2	SEEK_END
       L_SET	SEEK_SET
       L_INCR	SEEK_CUR

       L_XTND	SEEK_END

       SVR1-3 returns long instead of off_t, BSD returns int.

       Note that file descriptors created by dup(2) or fork(2) share the  current  file  position
       pointer, so seeking on such files may be subject to race conditions.

SEE ALSO
       dup(2), fork(2), open(2), fseek(3)

Linux					    2001-09-24					 LSEEK(2)


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