How to use my logging class like a std C++ stream?

Question

I've a working logger class, which outputs some text into a richtextbox (Win32, C++). Problem is, i always end up using it like this:

stringstream ss;  
ss << someInt << someString;  
debugLogger.log(ss.str());

instead, it would be much more convenient to use it like a stream as in:

debugLogger << someInt << someString;

Is there a better way than forwarding everything to an internal stringstream instance? If'd do this, when would i need to flush?

Answer 1

You need to implement operator << appropriately for your class. The general pattern looks like this:

template <typename T>
logger& operator <<(logger& log, T const& value) {
    log.your_stringstream << value;
    return log;
}

Notice that this deals with (non-const) references since the operation modifies your logger. Also notice that you need to return the log parameter in order for chaining to work:

log << 1 << 2 << endl;
// is the same as:
((log << 1) << 2) << endl;

If the innermost operation didn't return the current log instance, all other operations would either fail at compile-time (wrong method signature) or would be swallowed at run-time.

Answer 2

Overloading the insertion operator<< is not the way to go. You will have to add overloads for all the endl or any other user defined functions.

The way to go is to define your own streambuf, and to bind it into a stream. Then, you just have to use the stream.

Here are a few simple examples:

• Logging In C++ by Petru Marginean, DDJ Sept 05th 2007
• Rutger E.W. van Beusekom's logstream class, check also the .hpp alongside with this file