Re: Method call directed off null pointer - legal?

Hello All,

We have a debate going on here about the following snippet of code (see
below) and the "legality" of it.

The chief issue at hand is of course, the use of p->IsNull( ) when p = 0.
The programmer who wrote this code thinks it is okay because the "this"
pointer is "just passed as an argument". It certainly compiles clean and
runs OK on Microsoft Visual C++ 2008.

Any opinions on this code will be well received. Subjectively I dislike this
code immensely, but are there rules in the standard that indicate that this
code is illegal? For example, undefined behaviour on different
architectures? I have instructed the programmer to change it to a static
method and pass the argument in, instead.

PS: Some of you will question why we have an IsNull( ) test in the first
place, as opposed to testing p == 0 directly. Whilst it isn't really
relevant to the question, the reason is that the set of classes in question
is designed to allow a developer to formulate an expression tree using code,
which introduces ambiguity when you want to operate *on* the tree as opposed
to constructing a tree. IsNull( ) exists to alleviate ambiguity in the
intent of the code, when operating *on* the tree.

Thanks

Kevin

---------------------------------------

#include <iostream>

using namespace std;

class Fred
{
    public:
    bool IsNull( ) { return ( ( void* )this ) == 0; }

};

int main( )
{
    Fred* pFred = 0;

    if( pFred->IsNull( ) )
       cout << "It is null.\n";

    return 0;

}