TITLE: Detecting null references


PROBLEM: euamts@eua.ericsson.se (Mats Henricson), 1 Jun 92

What is the standard way to indicate failure with a function which 
returns a reference.  In my C programs, when I want to indicate failure
I just returned NULL.  But I am currently working on a table object
which I would like to return a refernce when sent the message lookup(key),
(is this a good place to use pointers?  I'm trying to get away from the habit
of writing C code in my C++ programs)  I have no exceptions or anything, I'm
using Borland C++ v2.0
 

PROBLEM: weikart@prl.dec.com (Chris Weikart), 1 Jun 92
         DEC Paris Research Lab (PRL)


I recommend this approach. Furthermore, to avoid name-space pollution, I
recommend that these kinds of `null' objects be defined as static class
members. For example:

header:
	class aString
	{
	    ...
	    static const aString Null;
	    static const char null;
	    ...
	};

source:
	const aString aString::Null ((char *)NULL);
	const char aString::null = '\0';

client:

	aString foo;
	...
	if (foo == aString::Null || foo[0] == aString::null)
	    // whatever


[ Our convention is to pass arguments as pointers. Perhaps this might
  be an acceptable alternative. -adc ]