Some people use Protobufs to solve this, but when I work with C++, I use a class that takes a (data, size) as an input (to its constructor), and implements an overridable Get<T> method.

So you can do: auto s = datasource.Get<std::string>();

For each type I need I override Get<T> for that type. If the data source class is out of data, I throw a specific exception, that I catch at the global level. This works like a breeze and the advantage over protobufs is that it's faster (no Protobuf parsing overhead, errors) and you never consume more than you need.