HP 3000 Manuals HP 3000 Manuals
lseek
Repositions a read/write file offset.
Syntax
#include <sys/types.h>
#include <unistd.h>
off_t lseek (int fildes, off_t offset, int whence);
Parameters
fildes An open file descriptor.
offset The number of bytes for the new offset. The application of
this value is defined by whence.
whence A value specifying how offset is to be applied to calculate
the resultant offset. Following are valid values and their
meanings (defined in <unistd.h>).
SEEK_SET Set new offset to offset.
SEEK_CUR Set new offset to offset plus the current
offset.
SEEK_END Set new offset to offset plus the current file
size.
Return Values
>=0 Success. The new file offset position is returned.
-1 An error occurred. The current offset is not changed, and
errno is set to indicate the error condition.
Description
The lseek() function sets the file offset for the open file description
associated with fildes to a new position defined by both the offset and
whence parameters. The file offset is the number of bytes from the
beginning of the file (where the beginning of the file is file offset 0).
The lseek() function allows the file offset to be set beyond the end of
existing data in the file. If data is later written at this point,
subsequent reads of data in the gap return bytes with the value zero
until data is actually written into the gap; however, the lseek()
function cannot, by itself, extend the size of a file.
Implementation Considerations
Refer to the ESEEK and ESYSERR error descriptions below.
Pipes (or FIFOs) and device special files are not supported.
Errors
If an error occurs, errno is set to one of the following values:
EBADF CAUSE The fildes parameter is not a valid open file
descriptor.
ACTION Check to see if fildes has been altered or is not
initialized.
EINVAL CAUSE The whence parameter is not a valid value, or the
resulting file offset would be invalid.
ACTION Check if value contained by whence exceeds the file
limit or is a negative value.
ESEEK CAUSE The fildes parameter does not refer to a file that
supports seeking.
ACTION Certain files or devices do not support seeking.
Make sure that the program is not attempting to seek
on those files.
ESYSERR CAUSE An operating system error has occurred that does not
map directly to any of the above errors.
ACTION Examine the MPE/iX error stack for the type of system
error.
See Also
creat(), dup(), open(), read(), sigaction(), write(), <unistd.h>, POSIX.1
(Section 6.5.3)