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lseek(2)
NAME
  lseek - Move read-write file offset

SYNOPSIS
  #include <sys/types.h>
  #include <unistd.h>

  off_t lseek(
	  int filedes,
	  off_t offset,
	  int whence );

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  lseek(): XSH4.0, XSH4.2, XSH5.0, XNS4.0, XNS5.0

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  filedes
      Specifies a file descriptor obtained from a successful open() or
      fcntl() function.

  offset
      Specifies a value, in bytes, that is used in conjunction with the
      whence parameter to set the file pointer. A negative value causes
      seeking in the reverse direction. The resulting file position may also
      be negative.

  whence
      Specifies how to interpret the offset parameter in setting the file
      pointer associated with the filedes parameter.  Values for the whence
      parameter are:

      SEEK_SET
	  Sets the file pointer to the value of the offset parameter.

      SEEK_CUR
	  Sets the file pointer to its current location plus the value of the
	  offset parameter.

      SEEK_END
	  Sets the file pointer to the size of the file plus the value of the
	  offset parameter.

DESCRIPTION
  The lseek() function sets the file offset for the open file specified by
  the filedes parameter. The whence parameter determines how the offset is to
  be interpreted.

  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,
  subsequently reading data in the gap returns bytes with the value 0 (zero)
  until data is actually written into the gap.

  By itself, the lseek() function does not extend the size of the file.

RETURN VALUES
  Upon successful completion, the resulting pointer location (the file
  offset), measured in bytes from the beginning of the file, is returned. If
  the lseek() function fails, the file offset remains unchanged, a value of
  (off_t) - 1 is returned, and errno is set to indicate the error.

ERRORS
  If the lseek() function fails, the file offset remains unchanged and errno
  may be set to one of the following values:

  [EBADF]
      The filedes parameter is not an open file descriptor.

  [EINVAL]
      The whence parameter is an invalid value or the resulting file offset
      would be invalid.

  [ESPIPE]
      The filedes parameter is associated with a pipe (FIFO), a socket, or a
      multiplexed special file.

      The filedes parameter underlying the stream is associated with a
      socket.

SEE ALSO
  Functions: fcntl(2), fseek(3), open(2), read(2), write(2)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for L

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