Re: Context logging at a class level

On Dec 17, 2004, at 10:59 AM, Ben Arnold wrote:

> Hi,
>
> I have a (hopefully) simple question about getting context information 
> into
> my logging.
>
> Say I have a class Agent:
>
> class Agent {
> public:
>   long id() const { return myId_; }
>   void doSomething();
>
> private:
>   static LoggerPtr agentLogger_;
> };
>
> This agent is connected to by a number of IP clients, and there are a 
> number
> of agents in the system (each with their own ID)
>
> I can use NDC to log the IP of the connecting client for all my logging
> within the doSomething function, which is good.  However I would also 
> like to
> include the agent's ID implicitly without having to include it in each 
> call
> to .info() or .debug() etc.

You could use MDC to hold the agent ID (it could also hold the IP).

MDC::set("IP", ip);
MDC::set("agent", itoa(id()));

and then use an %X{agent} specification in your layout.



> So rather than...
> agentLogger->info( "Agent " + id() + " processing request" );
> (please assume that there is a nice way to concatenate a log4cxx 
> string with
> a long, that's merely for ease of reading)

In the current CVS and the forthcoming 0.9.8, you might want to 
consider the stream-like interface provided in log4cxx/stream.h.  The 
code would be like:

//
//   not thread safe, so it should not be static
//   typically created at entry to methods that use it
logstream agentStream(agentLogger, Level::INFO);

agentStream << Level::INFO << "Agent " << id() << " processing request" 
<< LOG4CXX_ENDMSG;


0.9.7 and previous allowed "insertion fragments" to appear in the 
macros, but that is no longer supported:

LOG4CXX_INFO(agentLogger, "Agent " << id() << "processing request");