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lseek(2)
NAME
  lseek -  Moves 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():  XSH5.0, XNS4.0

  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.

	    [XNS4.0]  The filedes parameter underlying the stream is
	    associated with a socket.

RELATED INFORMATION
  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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