20 year old C++ has absolutely no chance to compile with a modern compiler unless it has a compatibility option for 20 year old C++ and you know how to enable it. i've had to fix 2 year old code when upgrading gcc.
Pretty sure gcc doesn't enable trigraphs unless you pass a command-line option to do so (and maybe it's included in -std or -ansi or something like that).
i've had issues with templates, but please forgive me if i don't provide specifics because it was ages ago. i've stopped doing C++ long before auto was even proposed so can't comment on that.
