Conference visa::ftsv

85.0. "effect of dsc$w_length in command descriptor" by AWECIM::HANNAN (Beyond description...) Wed Apr 02 1997 22:21

I get error 12 (access violation I believe) when I use callable FTSV (v3) 
and pass a descriptor with a length which exceeds the actual command string.  
Ie, the following produces the error 12:

  static char ftsv_command[512];
  $DESCRIPTOR (ftsv_command_dsc, ftsv_command);	/* dsc$w_length set to 512 */

  strcpy (ftsv_command, "copy a.dat b.dat");
  status = FTSV$FTSV (&ftsv_command_dsc);
  exit (status);

Problem is corrected by assigning the exact length of the passed string to
dsc$w_length, attempted as a last resort:

  static char ftsv_command[512];
  $DESCRIPTOR (ftsv_command_dsc, ftsv_command);	/* dsc$w_length set to 512 */

  strcpy (ftsv_command, "copy a.dat b.dat");
  ftsv_command_dsc.dsc$w_length = strlen(ftsv_command);	 /* prevents error 12 */
  status = FTSV$FTSV (&ftsv_command_dsc);
  exit (status);

Is this expected behavior ?  

Thanks,
Ken

>Is this expected behavior ?  

I don't know if ACCVIO is the *expected* behaviour. I'd be more inclined to 
say that what you were doing would produce "undetermined" results.

The length field in that kind of descriptor contains the number of bytes
USED in the string, not the allocation size.

Colin.

Thanks for the reply... C and $DESCRIPTOR leave a little to the imagination
to get em working right sometime depending on the target routine...

/Ken