Begin work on "debug mode" for libstdc++

[Doug Gregor]

Hello,
	I've begun work on a "debug mode" for libstdc++. The implementation 
will perform additional run-time checks to diagnose misuses of the 
standard library, such as an attempt to dereference a past-the-end 
iterator or insert into a container with an iterator from another 
container.
	The main feature of such an implementation is the addition of safe 
iterators to the library. Safe iterators keep track of the container 
they reference and their relationship with the container. Additionally, 
the implementation will contain annotations for standard library 
algorithms that verify the correctness of their arguments. The primary 
goal is to catch errors in the use of the library at the earliest point 
possible, before the errors result in memory corruption that makes 
debugging particularly nasty.
	Other standard libraries already have debug modes, including the 
Metrowerks standard library and STLport (see 
http://www.stlport.org/doc/debug_mode.html). The libstdc++ 
implementation will likely perform checks similar to those in existing 
implementations. If you are interested in a particular class of 
run-time checks not covered, please contact me.
	This work is supported by Apple, and will be primarily done in-house. 
We do intend to contribute this work back to the FSF sources as soon as 
it is feasible. The timeframe for this project is approximately two 
months.

	Thank you,
	Doug Gregor
	dgregor@apple.com