osf1 man page for lseek

lseek(2)							System Calls Manual							  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, XNS5.0

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

PARAMETERS
       Specifies  a  file descriptor obtained from a successful open() or fcntl() function.  Specifies a value, in bytes, that is used in conjunc-
       tion with the whence parameter to set the file pointer. A negative value causes seeking in the reverse direction. The resulting file  posi-
       tion may also be negative.  Specifies how to interpret the offset parameter in setting the file pointer associated with the filedes parame-
       ter.  Values for the whence parameter are: Sets the file pointer to the value of the offset parameter.  Sets the file pointer to  its  cur-
       rent  location  plus the value of the offset parameter.	Sets the file pointer to the size of the file plus the value of the offset parame-
       ter.

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 indi-
       cate the error.

ERRORS
       If the lseek() function fails, the file offset remains unchanged and errno may be set to one of the following values: The filedes parameter
       is  not	an  open  file	descriptor.   The whence parameter is an invalid value or the resulting file offset would be invalid.  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.

RELATED INFORMATION
       Functions: fcntl(2), fseek(3), open(2), read(2), write(2)

       Standards: standards(5) delim off

																	  lseek(2)