= Error handling in Orxonox =
[[TracNav(TracNav/TOC_Development)]]

Whenever something unwanted happens, the programmer needs to react in a certain way.[[br]]
We support three different ways to handle such situations:
 * Display a message in the console, shell and log
 * Throw an exception that can be caught
 * Abort the program with a message
[[br]]

== COUT(#), displays messages ==
Whenever you want to show the user or the programmer a message, use COUT(#) where # is a number denoting the output [wiki:Debug level]. [[br]]

'''Note: A simple message with level 1 doesn't trigger an exception or anything yet!''' [[br]]

== Exceptions ==
This kind of error handling method is used when the programmer has to handle situations that could go wrong, but shouldn't. Mind the difference to Assertions below! [[br]]
For information about how to use them, see [wiki:Exception Exceptions]. [[br]]
A good example for exceptions would be a script compiler. Whenever it encounters bad tokens, it throws an exception with a message. The function calling the parser can then catch that exception, display it and act accordingly. [[br]]
We also use Exceptions when loading a level. If one occurs, we can abort and the user can choose another level. Of course this shouldn't happen, but nobody's perfect. [[br]][[br]]
Keep in mind that you yourself have to display the exception message at the right spot (they do get displayed automatically in level 4 however).


== Assertions ==
Last but not least: Assertions. This is very handy programmer's tool. It helps a lot tracking bugs and sets up a newly created class much quicker. [[br]]
When should you use it? Basically, an assertion is used when the programmers assumes that a certain condition is true and that otherwise the program would fail somewhere. In short: Whenever something should never go wrong and can't in the eyes of the programmer. But it mostly will ;)  [[br]][[br]]
An example: In a function, you receive a pointer and do something like ptr->aMemberFunction() while assuming that ptr != 0 because otherwise, you'll probably get a segmentation fault.

{{{
void fooBar(myClass* ptr)
{
    ...
    ptr->aMemberFunction();
}
}}}

You can now insert a call to the 'asser()' macro so that whenever ptr == 0 the program aborts. Now this doesn't sound very helpful, but it is: First of all, the abort message tells you exactly where the error has happened (file, line, function). Secondly, the program would have aborted anyway because of the null pointer. [[br]][[br]]
The more asserts you insert, the easier bug tracking will be. You might even spot them before they could ever be triggered. [[br]][[br]]
'''Important: Asserts are only useful when the mistake is in the program. Throwing asserts for bad input doesn't help anyone, use exceptions then! [[br]]

Usage: 'assert(condition you assume);' or when you want to tell more use 'OrxAssert(condition, message)'. The message gets then displayed via COUT(1) before the assert() macro is called. [[br]]
The example above would then read:

{{{
void fooBar(myClass* ptr)
{
    ...
    OrxAssert(ptr != 0, "You screwed the wrong pointer!");
    ptr->aMemberFunction();
}
}}}