C++ – Custom stream to method in C++

cstream

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"; instead of CLogger->log("Testing, %i,2,3", 1);

My question is how would I do this? I don't want to directly create a stream to stdout as I want to use my own method which includes writing files and such. I've considered overloading with a certain struct that'd flush the current stream buffer to a method, but I'd have to do CLogger << flush << "Test!\n"; which is kind of odd.

Does anybody know how to do this?

Best Answer

If all that you need is directing certain log messages to files, have you considered std::ofstream?

Otherwise, I like to derive my logging class from std::ostream, so I get all of the stream goodness. The trick is to put all of your application-specific code in the associated streambuf class. Consider:

#include <iostream>
#include <sstream>

class CLogger : public std::ostream {
private:
    class CLogBuf : public std::stringbuf {
    private:
        // or whatever you need for your application
        std::string m_marker;
    public:
        CLogBuf(const std::string& marker) : m_marker(marker) { }
        ~CLogBuf() {  pubsync(); }
        int sync() {
            std::cout << m_marker << ": " << str();
            str("");
            return std::cout?0:-1;
        }

    };

public:
    // Other constructors could specify filename, etc
    // just remember to pass whatever you need to CLogBuf
    CLogger(const std::string& marker) : std::ostream(new CLogBuf(marker)) {}
    ~CLogger() { delete rdbuf(); }
};

int main()
{
    CLogger hi("hello");
    CLogger bye("goodbye");

    hi << "hello, world" << std::endl;
    hi << "Oops, forgot to flush.\n";
    bye << "goodbye, cruel world\n" << std::flush;
    bye << "Cough, cough.\n";
}

Notes:

  • The CLogger constructor can take whatever parameters you need to use -- a filename, an output language, a pointer to the underlying log data, whatever. Just pass the data onto the CLogBuf class.
  • The CLogBuf's sync() is automatically called during in response to std::flush.
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