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Re: Taking the address of a convenience variable value
- From: Daniel Jacobowitz <drow at false dot org>
- To: Andrew Cagney <cagney at gnu dot org>
- Cc: Bob Rossi <bob at brasko dot net>, Paul Dubuc <pdubuc at cas dot org>,GDB Mailing List <gdb at sources dot redhat dot com>
- Date: Wed, 26 May 2004 13:31:00 -0400
- Subject: Re: Taking the address of a convenience variable value
- References: <40B37A92.6020106@cas.org> <20040525235958.GA30063@white> <40B4D2D2.3000700@gnu.org>
On Wed, May 26, 2004 at 01:24:34PM -0400, Andrew Cagney wrote:
> >On Tue, May 25, 2004 at 12:55:46PM -0400, Paul Dubuc wrote:
> >
> >>>In the June 2004 issue of the C/C++ User's Journal (p. 24) there is an
> >>>article on how to write user-defined commands for gdb to examine the
> >>>contents of STL vectors, sets and maps. It looks extremely useful, so I
> >>>decided to try it modifying the commands for use with the GCC STL, but I
> >>>can't get some of the commands for sets and maps to work. It relies on
> >>>a tecnique that involves being able to take the address of a convenience
> >>>variable value, for example:
> >>>
> >>> set $maptype = &$arg0._M_t._M_header->_M_value_field
> >>> set $maptypep = &$maptype
> >>>
> >>>When I try this the 2nd statement gives me the error message
> >>>
> >>> Attempt to take address of value not located in memory.
>
> As you note, its trying to take the address of a convenience variable -
> since convenience variables do not live in the inferior they don't have
> an address.
>
> Does:
>
> set $maptype = &$arg0._M_t._M_header->_M_value_field
> set $maptypep = &&$arg0._M_t._M_header->_M_value_field
>
> or:
>
> set $maptype = $arg0._M_t._M_header->_M_value_field
> set $maptypep = &$arg0._M_t._M_header->_M_value_field
>
> make sense?
>
> The other, sigh, possability is that this was a ``feature'' and there's
> been a regression :-/
Or that it never worked in the FSF tree at all. There's a reference
below to HP-UX - could this be HP's hacked GDB sources?
> What does:
>
> (gdb) paddr &$arg0._M_t._M_header->_M_value_field
>
> display?
I don't think GDB has a paddr command?
--
Daniel Jacobowitz