Tag: assert

Do you know the assert-macro? It is an easy tool for debugging: You can use it to
check if a pointer is a NULL-pointer or if your application is in a proper state
for processing. When this is not the case, if will stop your application,
when you are using a debug mode, in release mode normally nothing happens.
Depending on your platform this can vary a little bit. For instance the
Qt-framework prints a log-message if you have a failed assert test to stderr when
you are currently using a release build. So assert is a nice tool to check
pre-conditions for you function / method. And you will see your application crashing
when this precondition is not fulfilled. Thanks to some preprocessor-magic the
statement itself will be printed to stdout. So when you are writing something
like:

void foo( bar_t *ptr ) {
  assert( NULL != ptr );
  ...
}

and your pointer is a NULL-pointer in your application you will get some info on
your stdout like:

assert in line 222, file bla.cpp: assert( NULL != ptr );

Great, you see what is wrong and you can start to fix that bug. But sometimes you
have to check more than one parameter or state:

global_state_t MyState = init;

void foo( bar_t *ptr ) {
  assert( NULL != ptr && MyState == init );
  ...
}

Nice one, your application still breaks and you can still see, what went wrong?
Unfortunately not, you will get a message like:

assert in line 222, file bla.cpp: assert( NULL != ptr && MyState == init );

So what went wrong, you will not be able to understand this on a first look.
Because the pointer could be NULL or the state may be wrong or both of the tests
went wrong. You need to dig deeper to understand the error.
For a second developer this will get more complicated, because he will most likely
not know which error case he should check first, because he didn’t wrote the code.s
So when you have to check more than one state please use more than one assert:

global_state_t MyState = init;

void foo( bar_t *ptr ) {
  assert( NULL != ptr );
  assert( MyState == init );
  ...
}

Thanks!