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From: jimad@microsoft.UUCP (Jim ADCOCK)
Newsgroups: comp.lang.c++
Subject: references to dereferenced null pointers
Message-ID: <51083@microsoft.UUCP>
Date: 27 Feb 90 18:42:23 GMT
Reply-To: jimad@microsoft.UUCP (Jim ADCOCK)
Organization: Microsoft Corp., Redmond WA
Lines: 41

/********

Is the following program legal, illegal, or undefined?  

[It compiles and runs "correctly" under cfront 2.0]

The program deals with the issue of the reference equivalent to a null
pointer -- ie what one would get if one could dereference a null pointer
and asssign the result to a reference.  As the following shows, at least
under cfront 2.0, the dereference followed by assignment to a reference is
a conceptual dereference only  --not actually done in machine code--  and
thus causes no null-pointer fault.  While the following example is weak,
I claim assigning a "null" to a reference is useful when defining 
iterators returning references rather than pointers.

[I don't believe this issue is covered in the C++ references]

********/

class OW
{
    char ow[4];
public:
    OW(char* p) { strncpy(ow, p, 4); }
    void print() { printf("%s ", ow); }
};

OW how("how"); OW now("now"); OW bow("bow"); OW wow("wow");
OW* pow[] = { &how, &now, &bow, &wow, 0 };

int main()
{    
    int i = 0;
    while (1)
        {
        OW& row = *pow[i++];
        if (!&row) break;
        row.print();
        }
    return 0;
};