line_inserter

line_inserter.cpp

#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>

class insertbuf : public std::streambuf
{
public:
    insertbuf(std::ostream& os, std::string const& data)
        : m_stream(os)
        , msg(data)
    { }

    int_type overflow(int_type c)
    {
        static bool newline(true);
        if (c != traits_type::eof() && newline)
        {
            m_stream.write(msg.data(), msg.size())
                 ? traits_type::not_eof(c) : traits_type::eof();
        }
        
        newline = traits_type::eq(traits_type::to_char_type(c), '\n');

        return m_stream.put(traits_type::to_char_type(c))
             ? traits_type::not_eof(c) : traits_type::eof();
    }
    
    int sync() { return m_stream.rdbuf()->pubsync() ? 0 : -1; }
private:
    std::ostream& m_stream;
    std::string msg;
};

class line_inserter : private insertbuf, public std::ostream
{
public:
    line_inserter(std::ostream& os, std::string const& data)
        : insertbuf(os, data)
        , std::ostream(this)
    { }
};