creating an ostream

Question

I am trying to create a c++ ostream for educational reasons. My test will be creating an ostream that acts like a ofstream would except instead of writing to a file it would write to a deque or vector container.

Answer 1

As it is for education, as you say, i will show you how i would do such a thingy. Otherwise, stringstream is really the way to go.

Sounds like you want to create a streambuf implementation that then writes to a vector / deque. Something like this (copying from another answer of me that targeted a /dev/null stream):

template<typename Ch, typename Traits = std::char_traits<Ch>,
         typename Sequence = std::vector<Ch> >
struct basic_seqbuf : std::basic_streambuf<Ch, Traits> {
     typedef std::basic_streambuf<Ch, Traits> base_type;
     typedef typename base_type::int_type int_type;
     typedef typename base_type::traits_type traits_type;

     virtual int_type overflow(int_type ch) {
         if(traits_type::eq_int_type(ch, traits_type::eof()))
             return traits_type::eof();
         c.push_back(traits_type::to_char_type(ch));
         return ch;
     }

    Sequence const& get_sequence() const {
        return c;
    }
protected:
    Sequence c;
};

// convenient typedefs
typedef basic_seqbuf<char> seqbuf;
typedef basic_seqbuf<wchar_t> wseqbuf;

You can use it like this:

seqbuf s;
std::ostream os(&s);
os << "hello, i'm " << 22 << " years old" << std::endl;
std::vector<char> v = s.get_sequence();

If you want to have a deque as sequence, you can do so:

typedef basic_seqbuf< char, char_traits<char>, std::deque<char> > dseq_buf;

Or something similar... Well i haven't tested it. But maybe that's also a good thing - so if it contains still bugs, you can try fixing them.