lseek.2 (2010 09)

l
lseek(2) lseek(2)
NAME
lseek - move read/write file pointer; seek
SYNOPSIS
#include <unistd.h>
off_t lseek(int fildes, off_t offset, int whence);
DESCRIPTION
lseek() sets the file pointer associated with the file descriptor as follows:
• If whence is
SEEK_SET, the pointer is set to offset bytes.
• If whence is
SEEK_CUR, the pointer is set to its current location plus offset.
• If whence is
SEEK_END, the pointer is set to the size of the file plus offset .
These symbolic constants are defined in
<unistd.h>.
RETURN VALUE
When
lseek() completes successfully, it returns an integer, which is the resulting file offset as meas-
ured in bytes from the beginning of the file. Otherwise, a value of
-1 is returned and errno is set to
indicate the error.
For all files that are not character or block special files, the integer returned on successful completion is
non-negative. For character or block special files that correspond to disk sections larger than 2 gigabytes,
a non-negative integer is returned for successful seeks beyond 2 gigabytes. This value is the resulting file
offset as measured in bytes from the beginning of the file, when taken as an unsigned value.
-1 always
indicates an error return, even when encountered on greater than 2 gigabyte disk sections. The
lseek() call succeeds for NFS directories even if the resulting file offset becomes negative.
ERRORS
lseek() fails and the file offset remains unchanged if one or more of the following is true:
[EBADF] fildes is not an open file descriptor.
[ESPIPE] fildes is associated with a pipe, socket, or FIFO.
[EINVAL] whence is not one of the supported values.
[EINVAL] The resulting file offset would be negative.
[EINVAL] The resulting file offset would be a value which cannot be represented correctly in an
object of type off_t.
WARNINGS
Some devices are incapable of seeking. The value of the file offset associated with such a device is
undefined.
Using lseek() with a whence of SEEK_END on device special files is not supported and the results are
not defined.
SEE ALSO
creat(2), dup(2), fcntl(2), lseek64(2), open(2), unistd(5).
STANDARDS CONFORMANCE
lseek(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1