c++ - Add time stamp with std::cout

Question

I have the following code which is redirecting my std::cout output to a log file.

std::ofstream out("out.txt");
std::streambuf *coutbuf = std::cout.rdbuf(); //save old buf
std::cout.rdbuf(out.rdbuf()); //redirect std::cout to out.txt!

Now what I want is that whenever a newline is occurring, then the current time stamp will be written to the file.

I know I can achive this with:

std::cout << getTime() << "printing data" << std::endl;

But what I want is that of std::cout taking care of it automatically somehow. Is that possible?

Answer 1

I assume, that You want print the TimeStamp, if the first character of the next line appears in the output. Take a new class and inherit it from std::streambuf and connect it in the same way You do with the filebuf. If a newline-charater appears store this event in the object. Appears another character add the timestamp to the stream.

I wrote an example which use the RAII idiom for connecting the streambuf.

class AddTimeStamp : public std::streambuf
{
public:
    AddTimeStamp( std::basic_ios< char >& out )
        : out_( out )
        , sink_()
        , newline_( true )
    {
        sink_ = out_.rdbuf( this );
        assert( sink_ );
    }
    ~AddTimeStamp()
    {
        out_.rdbuf( sink_ );
    }
protected:
    int_type overflow( int_type m = traits_type::eof() )
    {
        if( traits_type::eq_int_type( m, traits_type::eof() ) )
            return sink_->pubsync() == -1 ? m: traits_type::not_eof(m);
        if( newline_ )
        {   // --   add timestamp here
            std::ostream str( sink_ );
            if( !(str << getTime()) ) // add perhaps a seperator " "
                return traits_type::eof(); // Error
        }
        newline_ = traits_type::to_char_type( m ) == '
';
        return sink_->sputc( m );
    }
private:
    AddTimeStamp( const AddTimeStamp& );
    AddTimeStamp& operator=( const AddTimeStamp& ); // not copyable
    // --   Members
    std::basic_ios< char >& out_;
    std::streambuf* sink_;
    bool newline_;
};

call an object of this class in following way:

// some initialisation ..
{
    AddTimeStamp ats( cout ); // timestamp is active
    // every output to 'cout' will start with a 'getTime()' now
    // ...
} // restore the old streambuf in the destructor of AddTimeStamp