[REVIEW] Null pointer passed as an argument to a 'nonnull' parameter in tools/source/generic/poly.cxx

[Stephan Bergmann]

On 02/16/2012 09:43 PM, julien2412 wrote:
> /home/julien/compile-libreoffice/libo/tools/source/generic/poly.cxx:91:9:
> warning: Null pointer passed as an argument to a 'nonnull' parameter
>          memset( mpPointAry, 0, nInitSize );
>          ^       ~~~~~~~~~~
> 1 warning generated.
>
> Here are the lines :
>       78 ImplPolygon::ImplPolygon( sal_uInt16 nInitSize, sal_Bool bFlags  )
>       79 {
>       80     if ( nInitSize )
>       81     {
>       82         mpPointAry = (Point*)new
> char[(sal_uIntPtr)nInitSize*sizeof(Point)];
>       83         memset( mpPointAry, 0, (sal_uIntPtr)nInitSize*sizeof(Point)
> );
>       84     }
>       85     else
>       86         mpPointAry = NULL;
>       87
>       88     if( bFlags )
>       89     {
>       90         mpFlagAry = new sal_uInt8[ nInitSize ];
>       91         memset( mpPointAry, 0, nInitSize );<<<<<  HERE
>       92     }
>       93     else
>       94         mpFlagAry = NULL;
>       95
>       96     mnRefCount = 1;
>       97     mnPoints = nInitSize;
>       98 }
>
[...]
>
> Cppcheck updated today doesn't detect this problem so I confirm fdo#39596
> could be useful :-)
> (could also be a cppcheck enhancement proposal, I didn't check if it had
> already been proposed)

The irony is that, while it apparently found a genuine bug here, the 
compiler's reasoning might actually be wrong.  I'm not 100% sure, but if 
C only requires that the first argument to memset must be non-null if 
the third argument is non-zero, then the compiler would obviously not be 
correct in flagging the above code.

Stephan