Introduction
This is version 0.1 of the CLog Class Hierarchy, so bear with me. This is the second revision
of this article, I hope this new version is better!
Here is a class heirarchy designed to simplify logging of messages
on a Windows platform. I should qualify and say that porting these classes to
*nix is trivial. It should be obvious that the CEventLogAppender would need
to be scrapped or retasked.
These classes are inspired by log4j. I was introduced to log4j which is a
sub project of Apache Jakarta by a friend. The website is a great place to
get more information, check it out at
http://jakarta.apache.org/log4j/docs/index.html
My main reason for checking out log4j in the first place was that I had been
told that my current method for logging was substandard. I did not believe
this of course. However, after 5 minutes of working with log4j, I knew
it for the truth! So, as a matter of course, I went on a quest, looking
for log4cpp. Well the log4j site has links to two different projects:
One at http://sourceforge.net/projects/log4cpp/;
and the other at http://log4cplus.sourceforge.net/
I checked them out and although they each have their merits, they were
too complicated for my taste. It was at this point that the CLog and
CLogAppender classes were born.
Purpose
I decided that I wanted to create a set of logging classes with really
simple, yet elegant, syntax. Something along the lines of
CLog myCLog(source);
myCLog.writeLog(debuglevel, message);
Well as it turns out, it's not quite that easy, but it's close.
How it works
The core concept to understanding the CLog hierarchy is the idea of
severity. Log messages are given a severity at the time they are
created. Log Appenders are given a severity threshold at the time
they are created. Then, when a message is sent with a severity
greater than the appender's threshold the message is logged.
This can be expressed more concisely as follows:
A message with severity x is written to a log appender with threshold y if x >= y.
Severity and threshold values are organized as follows:
debug < info < warn < error < fatal
Severity/Thresholds
debug
Detailed programmatic informational messages used as an aid in
troubleshooting problems by programmers.
info
Brief informative messages to use as an aid in troubleshooting
problems by production support and programmers.
warn
Messages intended to notify help desk, production support and
programmers of possible issues with respect to the running
application.
error
Messages that detail a programmatic error, these are typically
messages intended for help desk, production support,
programmers and occasionally users.
fatal
Severe messages that are programmatic violations that will
usually result in application failure. These messages are
intended for help desk, production support, programmers and
possibly users.
What all this gobbledegook means is that you, as the programmer,
has the duty to create meaningful messages and assign them the
proper severity. If you are good at this, then, you will reap
the benefit of incredibly informative logs with a standardized
look and feel making everyone's life easier.
Project Files
This set of classes consists of a number of files; I will lay them
out here for your perusal with a brief description.
Header files
- Utility.h
- contains a number of useful helper data structures
- Log.h
- the main
CLog Class Definition
- LogAppender.h
- the abstract
CLogAppender Class Definition that the
specific log appenders are derived from
- ConsoleLogAppender.h
- the specific Console log appender class definition
- FileLogAppender.h
- the specific File log appender class definition
- EventLogAppender.h
- the specific Event log appender class definition
Implementation files
- Utility.cpp
- contains a number of useful helper data structures
- Log.cpp
- the main
CLog Class Implementation
- LogAppender.cpp
- the abstract
CLogAppender Class Implementation
- ConsoleLogAppender.cpp
- the specific Console log appender class implementation
- FileLogAppender.cpp
- the specific File log appender class implementation
- EventLogAppender.cpp
- the specific Event log appender class implementation
The test application (driver)
- LogDriver.cpp
- the simple test application that will use the log and
log appender class to write to the console, test.dat,
and the event log.
Trying it out
In order to use the logging classes here is a description of what is required.
- You will need to create a .cpp file that will 'drive' the logger - in my case
this was LogDriver.cpp.
- include log.h, this will bring in the needed definitions, etc.
#include "/inc/log.h"
- instantiate an instance of the
CLog class, this will be the 'source' of log
messages
CLog myLog("LogDriver");
- instantiate and add as many log appenders as you like
CConsoleLogAppender * pConsoleLogAppender
= new CConsoleLogAppender(nsCLog::info);
CFileLogAppender * pFileLogAppender
= new CFileLogAppender(nsCLog::warning, "test.dat");
CEventLogAppender * pEventLogAppender
= new CEventLogAppender(nsCLog::debug);
myLog.addAppender(pConsoleLogAppender);
myLog.addAppender(pFileLogAppender);
myLog.addAppender(pEventLogAppender);
- write to the log(s) througout your codebase
myLog.writeLog(nsCLog::warning, "This is my test log message");
What you will have done is this:
- Created a logger that's source is "LogDriver"
- Created a log appender for console messages
- Created a log appender to write to test.dat
- Created a log appender to write to the event log
- Told the LogDriver logger about the 3 appenders
- Written to the various logs
What the messages will look like is:
01052002_124658 | LogDriver | warning | This is my test log message
The event log message is going to appear a little differently, but basically
the same. Because I'm lazy it will probably be like:
The entry in Event Viewer:
Type: Error
Date: 1/5/2002
Time: 12:46:58 PM
Source: LogDriver
Category: (1500)
Event: 0
User: N/A
Computer: Your Computer Name
The message (double click the entry):
The description for Event ID ( 0 ) in Source ( LogDriver ) cannot be
found. The local computer may not have the necessary registry
information or message DLL files to display messages from a remote
computer. The following information is part of the event:
01052002_124658 | LogDriver | warning | This is my test log message.
Let me know what you think - preferably constructive if not positive,
I'm not asking for flames :).
Read the _todo.txt document before sending me 'it oughta do X!' messages.
Conclusion
That's it - really.
