Portably safe to pass NULL/zero to dynamic_cast?
C++NullDynamic CastC++ Problem Overview
Out of habit for checking null pointers, I have sometimes written:
MyClass * c = someBasePtr ? dynamic_cast<MyClass*>(someBasePtr) : 0;
if (c) {...
In effect, checking for a null pointer before passing to dynamic cast, and also checking the return.
I then read in the MSDN documentation
> A null pointer value is converted to > the null pointer value of the > destination type by dynamic_cast.
It appears then that I could remove the ?: construct safely. Is this C++ portable?
Such that the new code would be
MyClass * c = dynamic_cast<MyClass*>(someBasePtr);
if (c) {...
Of course presuming that someBasePtr is either null or valid, i.e. not wild pointing to garbage...
C++ Solutions
Solution 1 - C++
§5.2.7/4:
> If the value of v is a null pointer > value in the pointer case, the result > is the null pointer value of type R.
So you don't have to check for a null pointer yourself. Same goes for operator delete, deleting a null pointer has no effect.
Solution 2 - C++
Yes, you can use dynamic_cast on a null pointer.
Solution 3 - C++
Yes, check 5.2.7.4 in standard.