Re: Taking the address of a convenience variable value

[Daniel Jacobowitz <drow at false dot 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