Re: Non-null pointers in C/C++?

>>> It's been some time since I started wondering why the C/C++ languages
>>> do not have a non-null pointer (something like a copyable C++
>>> reference)? [...]
>
>> and what happens if a null pointer gets passed as an argument to a 
>> non-null pointer parameter?
>
>It's undefined behaviour, but the compiler may be able to detect it and 
>issue a diagnostic.  

In that case, I think you just threw all the "safety" arguments out
the window.  If you're going to claim "safety" benefits, the compiler
needs to *CHECK*.  Of course, the issue is still there about what
to do when the check fails.  

In order to be useful, there has to be a way to convert a plain,
old, ordinary, unsafe pointer to a non-null pointer, provided, of
course that it p***** the check.  Here's a suggestion, but I'm sure
someone will think the syntax is horrible.  ifnotnull is not a
function, it's a syntax construct, sorta like if.  The assignment
in ifnotnull(nnp = np) is only done if the value is not null.
The syntax is:
	ifnotnull ( <no_steenking_null pointer variable> = 
	<dangerous pointer-valued expression ) 
		statement else statement;

Just for the heck of it, I'll make the else clause mandatory.


#include <stdlib.h>
	char	*p;
	char	no_steenking_null *nnp;

	p = malloc(...whatever...);
	ifnotnull (nnp = p) {
		... do something with nnp ...
		... like passing nnp to a function that takes ...  
		... no_steenking_null pointers ...
	} else {
		... pointer is null, handle it ...
	}

which is equivalent to:

#include <stdlib.h> 
	char	*p; 
	char	no_steenking_null *nnp;

	p = malloc(...whatever...);
	if (p != NULL) {
		nnp = (char no_steenking_null *) p;
		... do something with nnp ...
		... like passing nnp to a function that takes ...
		... no_steenking_null pointers ...
	} else {
		... pointer is null, handle it ...
	}

>And in a debug mode, it could also insert opcodes to 
>test for null at runtime.

I'll even go so far as to say that in debug mode, it would be a
good idea that converting *one* dangerous pointer to a not-null
pointer should, ideally, involve checking *all* not-null pointers
for being not null, to the extent possible.  This would at least
include all of the not-null pointers with declarations in scope.

Should we also forbid uninitialized not-null pointers?
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