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Subj:	RE: kbhit for VMS

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Date: Thu, 14 Mar 91 18:59 GMT
From: Louis Dunne <DUNNEL%saturn.eolas.ie@pucc.PRINCETON.EDU>
Subject: RE: kbhit for VMS
To: INFO-VAX@sri.com
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In reply to ...

>
>
>        Hi netters!
>
>        I've got a question, (last time I asked about SMG),  I've built a
>   program using   SMG$CREATE_VIRTUAL_KEYBOARD  and SMG$READ_COMPOSED_LINE
>   to use VMS's recall buffer.  I got what I wanted from DEC (Colorado)
>   and I revised and tested and finally got it to work.
>        Now the question I have is about a C routine available in Micro-Soft) C
>   called    kbhit    which allows you to interupt processing by typing any
>   key on the keyboard, I need this on the VAX, I can't seem to get
>                            SMG$READ_KEYSTROKE
>   to work under these conditions.  For example I'm reading in records
>   from a file, processing them, taking data from them and then I want to
>   stop - only not every time - in the middle of that to look at my screen,
>   I hit any key and the processing stops, I look at my screen, press any
>   key when I'm done looking and the read resumes where I left off.  If I
>   don't press any key it reads all through the file.
>
>   example:
>
>           while (!(kbhit())) {
>                blah
>                 blah
>                  blah
>           }
>
>   or
>       while((fgets(str,80,infile)) != NULL) /* reading a line from infile to s
   tr*/
>       {
>         if(kbhit())
>         {
>           getchar();
>           break;
>         }
>         line_num++;                              /* increment line counter */
>
>
>        I hope I am making sense to all of you, thanks again for your
>   help with SMG and I appreciate you getting back to me.
>
>
>                             Dwain A. Erhart
>                             NOSC PGC  San Diego
>
>   /********************************************************************/
>      I said WHAT!  No... what I meant was....
>   /********************************************************************/
>
>

   It seems to me that what you want to do, is to interrupt processing at
   any time when a key is hit, yes ?

   SMG allows you to do this easily; SMG$ENABLE_UNSOLICITED_INPUT is just the
   trick. Do the following :-

      Set up an AST (asynchronous system trap), i.e. just a routine in your
      C program, and send the address of this to the SMG routine (it also
      takes the pasteboard-id, and [optionally] an argument).
      Prototype your function as (e.g.) :-

         int ast ();

      Your function could be :-

         int ast (struct SMG$R_OUT_OF_BAND_TABLE *table)
         {
           printf ("key hit=%d", table->SSMG$R_CHAR_OVERLAY.SMG$B_CHAR);
         }

       You can get at your argument (such as a structure for your info.)
       using
          table->SMG$L_USER_ARG.

       The format/size of the character hit and arg. can vary (as far as I can
       remember), so you had best consult the manual for the SMG$ routines.

       Oh, lastly use the SMG$ENABLE_UNSOLICITED_INPUT routine to have your
       function invoked, at every keypress :-

          ret_code = SMG$ENABLE_UNSOLICITED_INPUT (pboard, ast, &some_struct);

          (Set this up in some initialisation code, or just around the parts
           where you need to detect the keypress.)

       To zap this 'trap' at any point use :-

          ret_code = SMG$DISABLE_UNSOLICITED_INPUT (pboard);

       Let me know if this is what you are looking for, I may have some code
       somewhere that uses this  (but exactly where is uncertain right now).

                                                      Louis Dunne.