As Ovid said, this sounds like a database.

But one option that might be a fit is to use Berkeley DB. That has both Perl and C++ interfaces (though you will have to pay a licensing fee to use it in a non-Open Source C++ program) and allows you to simultaneously access a very large (though simple) data structure in both languages and update it from either.

In reply to Re (tilly) 1: Frequently updating large datastructures by tilly
in thread Frequently updating large datastructures by Ntav

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