[Development] QLog ( Work on qDebug and friends)

[Lincoln Ramsay]

On 01/31/2012 03:32 PM, ext wolfgang.beck at nokia.com wrote:
> 1. Logging in a file:
 > 2. Enable or disable logging without recompiling your project.

I would like to comment on number 1.

I think it's important that a reasonably-unique default config file 
exists for each application. Why? Because without it, number 2 doesn't 
actually work.

I think a file name should be created based on the platform, and 
QCoreApplication properties like organizationName and applicationName 
(similar to QSettings).

On a Mac, you might end up with ~/Library/Application 
Support/OrganizationName/ApplicationName/Logging.txt

On Windows, you might end up with %HOMEDRIVE%%HOMEPATH%\App 
Data\OrganizationName\ApplicationName\Logging.txt

On Linux, you might end up with 
~/.config/OrganizationName/ApplicationName/Logging.txt

If you don't supply the organization or app names then perhaps a 
fallback to he binary name.


This then, is the "default" logging config file and we can document it 
reliably for each platform.

I think it's probably a good idea to leave in the setConfigFile method 
but I'd call it setDefaultConfigFile. This overrides the generated 
default and is useful for cases where you want multiple apps to pick up 
the same logging config file. It also allows app developers to keep the 
logging file with their other config/data if that location differs from 
where we used.

Finally, to give the user control, I think we need an environment 
variable that overrides both of the above. Say, QLOG_CONFIG_FILE. By 
setting this environment variable, the user can be certain that their 
logging config file will be used. It can also be used to cause multiple 
apps to use the same logging config file. Finally, it ensures the user 
can enable logging even if they don't have permission to write to the 
default config file.



In summary:
1) Generated default logging config file (for sanity).
2) QLog::setDefaultConfigFile for application writers.
3) QLOG_CONFIG_FILE for users.


Oh, and since there was no link to the change in your email, here it is:
http://codereview.qt-project.org/#change,13226

-- 
Lincoln Ramsay - Senior Software Engineer
Qt Development Frameworks, Nokia - http://qt.nokia.com/