[Cython] char* and NULL in log statements

[Martin C. Martin]

Stefan Behnel wrote:
> Hi,
> 
> Johannes Wienke wrote:
>> I've just noticed that using NULL values in char* is a bad idea when
>> converting them to a python string.
> 
> Every pointer can potentially be NULL. If Cython added NULL checks to
> everything that might be NULL, you'd get pretty inefficient code with loads of
> expensive conditionals. You should take care to write robust code yourself.

Actually, one of the lessons of JVM optimizations is that NULL checks 
are only a single instruction when they're not non-null.  You can tell 
the compiler to predict that the "non-null" will be taken, and when it 
is, there's no branch penalty.

However, I agree that it's against the spirit of C/C++, and hence 
Cython, to automatically check all pointers for null.

>> *Wouldn't it be a good idea to automatically convert them to None?*
> 
> What would be gained from having to check for None instead of having to check
> for NULL? Checking for NULL, referencing None and then checking for None is
> definitely more expensive than a straight check for NULL in your code.
> 
> If you *really* want None, then you can use something like this:
> 
>     cdef inline stringOrNone(char* value):
>          if value is NULL: return None
>          return value
> 
> and wrap all your char*->byte string conversions explicitly in a call to this
> function. Remember, explicit is better than implicit.
> 
> Stefan
> 
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