April 19, 1994 LSEEK 2

### NAME

lseek, seek - reposition read/write file offset

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```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

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, socket, or FIFO.

[```EINVAL`]
  ```whence` is not a proper value, or the resulting file offset would be invalid.

### SEE ALSO

dup(2), open(2)

### STANDARDS

The lseek(``) function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'') .

### BUGS

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