lseek man page on DigitalUNIX

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lseek(2)							      lseek(2)

       lseek - Move read-write file offset

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

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

       Interfaces  documented on this reference page conform to industry stan‐
       dards 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.

       Specifies  a  file  descriptor  obtained	 from  a  successful open() or
       fcntl() function.  Specifies a value, in bytes, that is	used  in  con‐
       junction	 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
       parameter.   Values for the whence parameter are: Sets the file pointer
       to the value of the offset parameter.  Sets the	file  pointer  to  its
       current location plus the value of the offset parameter.	 Sets the file
       pointer to the size of the file plus the value of the offset parameter.

       The lseek() function sets the file offset for the open  file  specified
       by  the filedes parameter. The whence parameter determines how the off‐
       set 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, sub‐
       sequently 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.

       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

       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

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

       Standards: standards(5)


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