Path: utzoo!attcan!uunet!aplcen!haven!adm!smoke!brl.mil!moss
From: moss@brl.mil (Gary S. Moss (VLD/VMB) <moss>)
Newsgroups: comp.windows.x
Subject: Re: "wake up" XtAppMainLoop (X <-> C IPC)
Keywords: XtAddInput, sockets
Message-ID: <14242@smoke.BRL.MIL>
Date: 25 Oct 90 18:54:56 GMT
References: <9954@uhccux.uhcc.Hawaii.Edu> <12053@ibism.uucp> <1990Oct24.124130.3273@ncsuvx.ncsu.edu>
Sender: news@smoke.BRL.MIL
Reply-To: moss@brl.mil
Organization: Ballistic Research Laboratory
Lines: 20

In article <1990Oct24.124130.3273@ncsuvx.ncsu.edu>, george@hobbes.ncsu.edu (George Browning) writes:
|> The X interface forks off the child C program and I utilize the above
|> piping to capture the output of the C program.  However, when an error
|> occurs I'd like to pass a message from the C program to the X interface
|> telling it to display an error dialog.
I did basically what you are trying to do by telling the C program to append
errors to a temporary file which I had already opened for writing errors from
the front-end X interface.  I use fopen to open the file for writing and
freopen to open it for reading in the front end, then call XtAppAddInput
right before XtAppMainLoop:

	(void) XtAppAddInput( apcon, fileno(errorfp), XtInputReadMask,
				displayLogMsg, (XtPointer) errorfp );

displayLogMsg plops the text into an AsciiTextWidget.

You could also set up a pipe for the child's stderr to go to which
XtAppAddInput would read from as Larry Poleshuck stated in his note.

-Gary