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 measured 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.
STANDARDS CONFORMANCE
lseek(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1
Printable version
