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3 - Tool #2 - Assertions
As a good programmer (aren't we all?) You've likely been exposed to assert() or a variant. Assert is used to, well, assert something:
assert(NULL!=ptr); // should never be null!
I've been using a modified version for many years now, called ASSERTING(). After recently reading a chapter on assertions in the book 'Game Programming Gems', I realized it was time to add a few features to the lowly assert, resulting in the following call:
ASSERTING(int test,const char *message);
Redoing the above example would give you:
ASSERTING( NULL!=ptr, "should never be null!");
Now, whenever the assertion fails (in this case, when ptr is NULL) the assertion 'fires', and the message "should never be null!" is displayed.
ASSERTING isn't a function, but rather a macro; it actually does quite a bit more than the above call implies:
- It can be turned off and on - when NDEBUG is defined (see assert2.h), it compiles away to nothing, handy for lean production code.
- It maintains a memory of where it is, so your assertion message also displays the file and line number of where the assertion is called.
- It displays three buttons, allowing you to continue execution, turn off the assertion, or quit.
The last feature needs more explanation.
Each failed ASSERTING() displays three buttons
in a window along with the assertion message:
'Continue', 'Ignore This Assert', or 'Exit
Program' ('Break to Debugger' on the emulator).
Continue does nothing, which means the assertion
will fire each time it is executed and fails.
'Ignore This Assert' allows you to turn off
the assertion, preventing future testing.
This can be especially useful for loops,
where you don't need the repeated assertions.
The third option is what I consider the handiest
feature of ASSERTING(). Typical assertions
use an abort() call or something similar
to exit. More often than not, what you really
want to do is look at the offending code
in the debugger. When run on the ebm, exiting
is the only option, and the program displays
'Exit Program'; but when run on the emulator,
the button displays 'Break to Debugger',
and will break into the debugger pointing
at the ASSERTING() call.
To use ASSERTING(), add assert2.cpp to your
makefle, and #include "assert2.h"
in your source. Add the call wherever you
wish. Remember that ASSERTING() is a macro,
and can be compiled out of the code - for
that reason always code it as if the line
might disappear (because with NDEBUG defined
it will!); always put it on a line by itself,
and watch out where it is placed.
Also avoid side effects - don't do a necessary
calculation in the ASSERTING() body, since
production code will be lacking that calculation
result. Finally, any time you turn on or
off NDEBUG, perform a 'make clean', and then
'make', so all source is recompiled with
the changes.
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