LSEEK(2)

NAME
lseek - reposition read/write file offset

SYNOPSIS
#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. The argument fildes must be an open file descriptor. Lseek repositions the file pointer fildes as follows:

    If whence is SEEK_SET, the offset is set to offset bytes. If whence is SEEK_CUR, the offset is set to its current location plus offset bytes. If whence is 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). Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined.

RETURN VALUES
Upon successful completion, lseek returns the resulting offset location 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.

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
POSIX, BSD 4.3

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

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