[boost] Re: Logging Library -- Formal Review Request

From: Daniel Frey (d.frey_at_[hidden])
Date: 2005-04-29 13:03:07

John Torjo wrote:
> I've just updated the Boost Log Library:
> http://torjo.com/code/logging-v132.zip

It's good to see progress on logging and what I've seen so far looks 
promising. However...

> BOOST_LOG(app) << "testing " << i << '-' << j << '-' << k  << std::endl;
> BOOST_LOG(dbg) << "this is a debug message, i=" << i << std::endl;
> BOOST_LOG(info) << "I just wanted to tell you something....";

...while I like the feeling of the stream approach from a user's 
perspective, there is one (IMHO important) feature that can not be 
implemented with it: Exception guards.

To illustrate my point, consider a "pure MACRO approach" like this:

std::string f()
{
    throw 42;
}

BOOST_LOG( app, "Huhu!" + f() );

where BOOST_LOG is:

#define BOOST_LOG( logger, message ) \
do { if( logger.is_enabled() ) { \
  try { logger.print( message ); } \
  catch( const std::exception& e ) { \
   logger.print( "Can't log \"" #message "\", e.what(): \"" + \
                 std::string( e.what() ) + "\"" ); \
  } \
  catch( ... ) { \
   logger.print( "Can't log \"" #message "\", unknown exception" ); \
  } \
} } while( false )

This feature helped us several times in the company when a log-message, 
calling some complicated functions, failed in a production system. As 
long as the above technique is applied, the log-file contains a good 
hint for us what's wrong and the product is still running without the 
customer noticing.

Regards, Daniel