Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!convex!iex!ntvax!doug
From: doug@ntvax.uucp (Douglas Scott)
Newsgroups: comp.windows.x
Subject: Storing data structure as a property
Summary: What am I doing wrong?
Keywords: properties, XChangeProperty, selections
Message-ID: <1989Nov29.072922.18738@ntvax.uucp>
Date: 29 Nov 89 07:29:22 GMT
Sender: Douglas Scott
Reply-To: doug@dept.csci.unt.edu (Douglas Scott)
Organization: CEMI, University of North Texas
Lines: 54

I have an application in which I wish to transfer a structure containing some
data between two instances of the same application, using the Selection
mechanism.  It is a small structure containing the name and size of a
temporary file (created by the requestee) wthat will be read by the requestor.
Since none of the standard format types or Atoms match what I am doing, I
figured I would just treat the struct as if it were just a string of raw
chars (as far as the property was concerned) and then recast it after it
is retrieved by the requestor:

store_selection(event)	/* loads selected region into cut buffer & property */
XSelectionRequestEvent *event;
{
	...

	ext_buff ext_info;	/* the struct with name & size of buffer */

		...in here the temp file is created, opened, written to,
		and closed in preparation for use by the requestor

		...

		/* set up the information struct to pass to requestor */

		strcpy(ext_info.name, bufname);
		ext_info.bufsize = c->bufsize;

		XChangeProperty(dpy,		/* load into property */
			event->requestor,	/* these are ok */
			event->property,
			event->target,
			format,			/* set to 8 */
			PropModeReplace,
			(char *) &ext_info,	/* cast as char array */
			(int) sizeof(ext_buff)); /* no. of bytes in struct */
		
...and so forth -- but as soon as XChangeProperty is called, I get:

XIO:  fatal IO error 32 (Broken pipe) on X server "woof:0.0"
      after 1388 requests (1388 known processed) with 0 events remaining.
      The connection was probably broken by a server shutdown or KillClient.

Is there a better way to send this data structure than as a char array?
Is there a format or size problem here?
Am I trying to do something illegal, and if so, why cant you send arbitrary
chunks of data as chars and recast on the other side?  I have my own Atom
type for this that I create with XInternAtom, so I am sure to send and recieve
something that both sides recognize.

Thank you in advance!

----------------------------------------------------------------------
Douglas Scott
Research Associate, CEMI, University of North Texas
doug@dept.csci.unt.edu