Question

I want to wrap a vector<char> with std::istream (so reading the vector would be done through the istream interface)

What’s the way to do it?

Answer 1

You’d define a streambuf subclass wrapping the vector, and pass an instance of that to the istream constructor.

If the data does not change after construction, it is sufficient to set up the data pointers using streambuf::setg(); the default implementation for the other members does the right thing:

template<typename CharT, typename TraitsT = std::char_traits<CharT> >
class vectorwrapbuf : public std::basic_streambuf<CharT, TraitsT> {
public:
    vectorwrapbuf(std::vector<CharT> &vec) {
        setg(vec.data(), vec.data(), vec.data() + vec.size());
    }
};

std::vector<char> data;
// ...
vectorwrapbuf<char> databuf(data)
std::istream is(&databuf);

If you need anything more advanced than that, override the streambuf::underflow method.