Taking the address of a convenience variable value

[Paul Dubuc <pdubuc@cas.org>]

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.

It doesn't work with gdb 5.3 or 6.1 on Solaris.  The author claims that it works 
on HP-UX, but I don't know why it would be any different.

Is there a way around this?  Or is there another source of user-defined commands 
that can be used to print the contents of STL containers in gdb?  Any help would 
be very much appreciated.

Thanks,
Paul Dubuc