wich version of g++ under snow leopard 10.6.1

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hi everybody I'm porting a software in c++ from windows to mac, the
target system is MacOsx Snow leopars 10.6.1
by default, i have G++ 4.0.1 installed.
what is the last version of g++ available on this system?
i saw G++ 4.2.1, is it the last one?
what will you recomment, what are exactly the imact using this version
or the other?
is there any link i can get this kind  of information?

thanks a lot