bsd man page for lseek

LSEEK(2)							System Calls Manual							  LSEEK(2)

NAME
       lseek - move read/write pointer

SYNOPSIS
       #include <sys/file.h>

       #define L_SET   0 /* set the seek pointer */
       #define L_INCR  1 /* increment the seek pointer */
       #define L_XTND  2 /* extend the file size */

       pos = lseek(d, offset, whence)
       off_t pos;
       int d;
       off_t offset;
       int whence;

DESCRIPTION
       The descriptor d refers to a file or device open for reading and/or writing.  Lseek sets the file pointer of d as follows:

	      If whence is L_SET, the pointer is set to offset bytes.

	      If whence is L_INCR, the pointer is set to its current location plus offset.

	      If whence is L_XTND, the pointer is set to the size of the file plus offset.

       Upon  successful  completion, the resulting pointer location as measured in bytes from beginning of the file is returned.  Some devices are
       incapable of seeking.  The value of the pointer associated with such a device is undefined.

NOTES
       Seeking far beyond the end of a file, then writing, creates a gap or "hole", which occupies no physical space and reads as zeros.

RETURN VALUE
       Upon successful completion, the current file pointer value is returned.	Otherwise, a value of -1 is returned and errno is set to  indicate
       the error.

ERRORS
       Lseek will fail and the file pointer will remain unchanged if:

       [EBADF]	      Fildes is not an open file descriptor.

       [ESPIPE]       Fildes is associated with a pipe or a socket.

       [EINVAL]       Whence is not a proper value.

SEE ALSO
       dup(2), open(2)

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

4th Berkeley Distribution					 February 24, 1986							  LSEEK(2)