Question

Greetings!

I’d like to make small program what reverses part of a stream between markers using stream effectors and/or manipulators For example:

From this:
cout << “something” << revstream::start << “asdf” << 3.14 << revstream::end << “something”;

To this:
something41.3fdsasomething

I’d like it to work not just on the standard cout and I’d like to embed them several times.

I’m new in c++ and my main problems are:
– I can’t create a new stream to store what is inside the markers
– How to reverse the temp stream?

I tried so many things and I stuck here:

class revstream {

 public:

    static ostream& start(ostream &os) { 
        //do the reversing
    return ???;
    }    

    static ostream& end(ostream &os) {

    return reversedstream;
    }   
};

Answer 1

You can do this, but it’s ugly as butt:

class revstream: public std::ostream
{
public:
    static std::ostream &start(std::ostream &os)
    {
        return *(new revstream(os));
    }

    static std::ostream &end(std::ostream &rev)
    {
        revstream *actual_rev= dynamic_cast<revstream *>(&rev);

        // logic for reversing output goes here

        std::ostream &result= actual_rev->os;
        delete actual_rev;

        return result;
    }

    revstream(std::ostream &in_os): std::ostream(&reversebuf), os(in_os)
    {
        return;
    }

    std::ostream &os;
    std::stringbuf reversebuf;
};

Your ostream manipulator has to return a reference to ostream, so you have to allocate within revstream::start.