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Date: Sun, 22 Oct 2006 22:48:00 -0000
From: Robert Dewar <dewar@adacore.com>
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To: Eli Zaretskii <eliz@gnu.org>
CC:  rodney.bates@wichita.edu,  gdb@sourceware.org
Subject: Re: breakpoint for accessing memory location
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Eli Zaretskii wrote:
>> Date: Sun, 22 Oct 2006 08:18:53 -0400
>> From: Robert Dewar <dewar@adacore.com>
>>
>> And it would lead to surprising results, if you watch p-p and p is
>> out of scope, it would be surprising if it did NOT lead to an error!
> 
> Strange, I'd actually expect GDB to tell me that "watch p-p" is an
> invalid command.  Something like
> 
>    Warning: attempt to watch constant expression.
> 
> I guess we have very different notions of what is reasonable in this
> context.

indeed!

I have no idea why you would think this is invalid, i.e. what the
general semantic rule is that makes this expression invalid.