HP 3000 Manuals

Accessing Files Programmer's Guide

Opening a System-Defined File 

System-defined file designators indicate those files that the file system
uniquely identifies as standard input/output devices for jobs and
sessions.  System-defined files are $STDIN, $STDINX, $STDLIST, $NEWPASS,
$OLDPASS, and $NULL. You cannot redefine characteristics for these files
once the process executing your code has been created, nor can you
backreference a file equation to redefine the characteristics for
a system-defined file designator.  For more information about
system-defined files, refer to Chapter 3, "Specifying a File Designator".

The following examples show two different ways that you can open
system-defined files using the indicated HPFOPEN options:

   *   "Opening $STDIN" shows an example of an HPFOPEN call that uses the
       designator option to open the job or session standard input device
       (see Example 5-3).

   *   "Opening $STDLIST" shows an example of an HPFOPEN call that uses
       the formaldesignator option to open the job or session standard
       list device (see example 5-4).

Opening $STDIN 

Example 5-3 is an HP Pascal/iX code segment containing an HPFOPEN
intrinsic call that uses only the designator option to open the
system-defined file $STDIN. $STDIN is the file designator associated with
your job or session's standard input device.  For an interactive session,
$STDIN is always a terminal keyboard.  For a batch job, $STDIN may be a
disk file or other input device.  You can also open a system-defined file
using only the HPFOPEN formaldesignator option (illustrated in Example
5-4).$STDIN, opening:files|

Example 5-3.  Opening $STDLIST Using HPFOPEN designator option 

     procedure open_standard_input_device

     const
        designator_option    = 5;     {defines HPFOPEN itemnum 5}

     var
        inputfile_num  : integer;  {required HPFOPEN filenum parameter}
        status         : integer;  {returns info if error/warning occurs}

        designator     : integer;  {declares HPFOPEN item 5           }

     begin
        inputfile_num  := 0;
        status         := 0;
        designator     := 4;       {Specifies $STDIN                      }

        HPFOPEN  (inputfile_num, status,
                  designator_option, designator,  {HPFOPEN designator option}
                  );

        if status <>0 then handle_file_error (inputfile_num, status);
     end;

If the HPFOPEN call is successful, a positive integer value is returned
in inputfile_num, and status returns a value of zero.  The file is now
open and can be read from.  If an error or warning condition is
encountered by HPFOPEN, status returns a nonzero value, thus invoking the
error-handling procedure handle_file_error.  For more information about
HPFOPEN parameters, refer to the MPE/iX Intrinsics Reference Manual 
(32650-90028).

Opening $STDLIST 

Example 5-4 is an HP Pascal/iX code segment containing an HPFOPEN
intrinsic call that uses the formaldesignator option to open the
system-defined file $STDLIST.

$STDLIST is the file designator associated with your job or session's
standard list device.  For an interactive session, $STDLIST is nearly
always a terminal screen.  For a batch job, $STDLIST is usually a line
printer.  You can also open $STDLIST using the HPFOPEN designator option 
(illustrated in Example 5-3).

Example 5-4.  Opening $STDLIST Using HPFOPEN formaldesignator option 

     procedure open_standard_list_device

     const
        formal_designator_option   = 2;     {defines HPFOPEN itemnum 2}

     type
        pac80  = packed array [1..80] of char;

     var
        listfile_num   : integer;  {required HPFOPEN filenum parameter}
        status         : integer;  {returns info if error/warning occurs  }

        file_name      : pac80;    {declares HPFOPEN item 2           }

     begin
        listfile_num   := 0;
        status         := 0;
        file_name      := '$stdlist'; {Specifies system-defined file      }
                                      {Blank is used as delimiter         }

        HPFOPEN  (listfile_num, status,
                  formal_designator_option, file_name,
                                              {formaldesignator option}
                  );

        if status <>0 then handle_file_error (listfile_num, status);
     end;

If the HPFOPEN call is successful, a positive integer value is returned
in listfile_num, and status returns a value of zero.  The standard list
device is now open and can be written to.  If an error or warning
condition is encountered by HPFOPEN, status returns a nonzero value, thus
invoking the error-handling procedure handle_file_error.

In appendix A, "HP Pascal/iX Program examples," example A-1 uses a
similar procedure to open $STDLIST. For more information about
HPFOPEN parameters, refer to the MPE/iX Intrinsics Reference Manual 
(32650-90028).

MPE/iX 5.0 Documentation