Custom stream to method in C++?

Question

I\'m making a logger and I wish to have some kind of stream-like happenings going on, ideally doing CLogger << \"Testing, \" << 1 << \",2,3\\n\";

Answer 1

I'm just going to copy-paste my current implementation of this below, it does all you need (and handles things like std::endl and the like). AMBROSIA_DEBUGis macro defined in debug builds, so in theory, every call to this output class should be omitted in release builds (haven't checked though, but seems logical overhead is kept to a minimum. The functionality is based on QDebug functionality, plus a little addition of mine debugLevel, which would allow you to filter debug messages by hand in your code depending on a runtime parameter. Right now it also adds the same amount of spaces before each message.

// C++ includes
#include 
#include 

typedef std::ostream& (*STRFUNC)(std::ostream&);

#ifdef AMBROSIA_DEBUG
    static int debugLevel;
    const static int maxDebugLevel = 9;
#endif

class Debug
{
public:

    #ifdef AMBROSIA_DEBUG
    Debug( const int level = 0 )
    : m_output( level <= debugLevel ),
      m_outputSpaces( true ),
      m_spaces( std::string(level, ' ') )
    #else
    Debug( const int )
    #endif // AMBROSIA_DEBUG
    {}

    template
    #ifdef AMBROSIA_DEBUG
    Debug& operator<<( const T &output )
    {
        if( m_output )
        {
            if( m_outputSpaces )
            {
                m_outputSpaces = false;
                std::cerr << m_spaces;
            }
            std::cerr << output;
        }
    #else
    Debug& operator<<( const T & )
    {
    #endif // AMBROSIA_DEBUG
        return *this;
    }
    // for std::endl and other manipulators
    typedef std::ostream& (*STRFUNC)(std::ostream&);
    #ifdef AMBROSIA_DEBUG
    Debug& operator<<( STRFUNC func )
    {
        if( m_output )
            func(std::cerr);
    #else
    Debug& operator<<( STRFUNC )
    {
    #endif // AMBROSIA_DEBUG
        return *this;
    }
private:
#ifdef AMBROSIA_DEBUG
    bool m_output;
    bool m_outputSpaces;
    std::string m_spaces;
#endif // AMBROSIA_DEBUG
};

Example usage:

int main()
{
    debugLevel = 9; // highest allowed in my app...
    Debug(4) << "This message should have an indentation of 4 spaces." << endl;
    Debug(8) << "This is a level 8 debug message.\n";
    return 0;
}