#include <string>

#include <sstream>

#include <iostream>

#include <iomanip>

// ... needed for debug

template< class type>

inline std::string to_string( const type & value)

{

    std::ostringstream streamOut;

    streamOut << value;

    return streamOut.str();

}

/////////////////////////////////////

// the 'str_stream' class

#ifdef NDEBUG

// Release mode

struct str_stream

{

    std::stringstream & underlying_stream() const

    { return m_streamOut; }

    operator std::string() const

    {

        return m_streamOut.str();

    }

private:

    mutable std::stringstream m_streamOut;

};

#else

// Debug mode

struct str_stream

{

    operator std::string() const

    {

        return m_str;

    }

    mutable std::string m_str;

};

#endif

template< class type>

inline const str_stream & operator<< ( const str_stream & out, const type & value)

{

#ifdef NDEBUG

    out.underlying_stream() << value;

#else

    out.m_str += to_string( value);

#endif

    return out;

}

int main()

{

    int nWordsCount;

    // ... calculate words count

    nWordsCount = 48;

    // this works

    std::string str = str_stream() << "We have " << nWordsCount << " words";

    // this DOES NOT work AS EXPECTED

    //

    // you would expect '0035', but get '35' in Debug Mode (wrong)

    // and '0035' in Release (correct);

    //

    // this would mean different behavior in Debug/ Release,

    // which you certainly don't want

    std::string str2 = str_stream() << std::setfill( '0') << std::setw( 4) << 35;

    std::cout << str2;

    std::cin.get();

    return 0;

}