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)? In my opinion, using non-null pointers instead of the
>"traditional" ones (wherever appropriate) would provide the following
>benefits:

So what's supposed to happen when the restriction is violated?  And
are YOU willing to be aboard a plane running this code in the
automatic pilot when the restriction is violated?  I can imagine
that it's really, really easy to have the function *definition*
declare the pointer arguments non-null but the declaration at the
point of use doesn't.  Guess what the undefined behavior will do?

>-allows restrictive programming techniques to be apllied at a lower
>cost (e.g. if a pointer passed to a function may not be null, there
>would be no need for a null-check before dereferencing it);

Yes, there really is a need for a null-check.  The question is what
to do (at runtime) when the check fails.

>-allow for improvements in programming practices (having two types of
>pointers will bring to attention the difference between them, namely
>the possibility that "traditional" pointers can be null, hopefully
>thus making it more obvious that "traditional" pointers should be
>checked for null before thay are dereferenced);

>-allow for more reliable code (having a "traditional" pointer where a
>non-null pointer would do increases the risk of undefined behavior; on
>the other hand, using a non-null pointer instead would be safer);

Is it really going to be more reliable to count on all the header files
containing the declarations to be fixed?

>-provide compilers with further semantic information, thus enabling
>them to perform more optimizations;
>-make source code more concise (as a result of having fewer null-tests
>when replacing "traditional" pointers with non-null ones).

In other words, attempting to completely hide the error-handling.

>What do you think?

fgets() returns a possibly-null pointer.  fputs() takes a non-null
pointer for the string to output.  Write the obvious copy loop to
copy a file to stdout.  The file open for the input has already
been done:

int display_file_to_stdout(FILE no_steenking_null *input);

Returns 0 on success, -1 on error.
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