HP 3000 Manuals

Accessing Files Programmer's Guide

Reading From $STDIN 

You can read data from your program's standard input device ($STDIN) by
using one of the following intrinsics:

   *   READ

   *   READX

   *   FREAD

The job/session input device is the source of all MPE/iX commands
relating to a job or session and is the primary source of all ASCII
information input to the job or session.  You can read a string of ASCII
characters from the job/session input device into an array in your
program with the READ and READX intrinsics.  The READ and READX
intrinsics are identical, except that the READX intrinsic reads input
from $STDINX instead of $STDIN. The $STDINX file is equivalent to $STDIN,
except that records with a colon (:)  in the first column of a line
indicate the end-of-file to $STDIN, and only the commands :EOD, and EOF
indicate the end of file for $STDINX.


NOTE  The READ and READX intrinsics are limited in their usefulness in
      that FILE commands are not allowed.  In addition, you cannot use
      the FCHECK intrinsic to determine error conditions encountered by
      READ or READX. You may find it more convenient (and a better
      programming practice) to use the HPFOPEN/FOPEN intrinsic to open
      the files $STDIN or $STDINX, then issue FREAD calls against these
      files.


If the standard input device ($STDIN) and the standard list device
($STDLIST) are opened with an HPFOPEN/FOPEN intrinsic call, the FREAD and
FWRITE intrinsics can be used with these devices.  For example, the FREAD
intrinsic can be used to transfer information entered from a terminal to
a buffer in the stack, and the FREAD intrinsic can be used to transfer
information from your stack directly to the standard list device.

Example 9-3 is an HP Pascal/iX code segment that uses the PRINT intrinsic
to prompt a user for a file designator, then uses the READ intrinsic to
read the input from $STDIN. Assume that the file designator is then
returned to a procedure that calls HPFOPEN to open a file with the
formaldesignator option passing the file name specified by the user.

Example 9-3.  Reading from $STDIN Using READ 

     procedure get_file_designator (var file_name : packed array [1..80] of
     char);

     var
        message         : packed array [..80] of char;  {holds prompt to user }
        length          : shortint;                     {length of prompt     }
        control_code    : shortint;                     {required by PRINT    }
        read_length     : shortint;                     {length read by READ  }
        expected_length : shortint;                     {size of message array}

     begin
        massage :='Please input a valid file reference'; {specify prompt      }
        length := -35;                                   {length of prompt    }
        control_code := 0                                {default condition   }
        expected_length := -80
        PRINT (message,
               length,
               control_code
              );
        if ccode <> cce then handle_file_error;
        else begin
              read_length := READ ( file_name,          {read data to output parm}
                                    expected_length     {length of file_name     }
                          );
              if ccode <> cce then handle_file_error;
          end
     end;

If an error is encountered by either READ or PRINT, procedure
handle_file_error is invoked.  For more information about READ
parameters, refer to the MPE/iX Intrinsics Reference Manual 
(32650-90028).  For more information about using the PRINT intrinsic,
refer to chapter 8, "Writing to a File".  For more information about
opening a file, refer to chapter 5, "Opening a File".  For more
information about file designators, refer to chapter 3, "Specifying a
File Designator".  In appendix A, "HP Pascal/iX Program Examples",
example A-2 uses a routine similar to example 9-3 to prompt the user for
a valid file reference.

MPE/iX 5.0 Documentation