[squid_demon]

Can someone please explain the purpose of a logging library (woof, log4j, etc)? There must be something beyond writing text to an external file, possibly with different error levels, that I'm missing. This is a serious question. I truly do not understand what you gain by depending on an external library for this (seemingly) simple operation and would appreciate some insight. Thanks!

[lfischer]

Often logging libraries allow you changing the logging level at runtime, without restarting or recompiling the application, as well as turning logs or off at runtime for different parts of the application. They let you organize logging levels so that when, for example, you turn the level to INFO in one part of the applications, all of the connected code also gets its own log level turned to INFO and you can define which parts of the application should change their log levels in sync. There's also performance considerations, often log libraries claim to implement tricks so that logging is supposed to be faster than naively writing strings to a file.

[alpaca128]

I was wondering the same, but a recent explanation made sense to me. The idea is to have the ability to control logging of third-party libraries. You might want to see some log messages but you don't want everything spamming stuff into stdout.

[the_af]

If it's just writing to a file or the screen you don't need much.

But then you need interpolation of arguments. And other appenders, what about logging to the network for aggregation elsewhere. And logging levels. And a couple more features and corner cases.

And before you know it, you're writing a lot of code which could be packaged into a library.

But you don't need to, like with most library stuff you could write it in-house yourself.