Checking if a string is null

[Derek Parnell]

On Thu, 26 Jul 2007 07:50:07 +0200, Frits van Bommel wrote:

> Derek Parnell wrote:
>> On Wed, 25 Jul 2007 14:29:47 +0100, Regan Heath wrote:
>> 
>>> Aside: If the location and length are identical you can short-circuit 
>>> the compare, returning true and ignoring the content, this could save a 
>>> bit of time on comparisons of large arrays.
>> 
>> I don't think this is such a good idea. How does one address the array of
>> four bytes at RAM location 4?
> 
> I'm pretty sure the only way to obtain such an array would be to have 
> already invoked Undefined Behavior (assuming 4 is an invalid memory 
> location on the platform the program's running on) and as such it 
> doesn't really matter whether or not two array references to it compare 
> equal or not...

There is no basis for assuming that any RAM location is not addressable. I
know that some operating systems prevent unprivileged programs from
accessing certain locations, and that some RAM is hardware-mapped to I/O
ports, but in theory, D as a system language should be able to address any
RAM location.

For example, if D had been implemented for the Amiga system, access to RAM
address 4 is vital. As that location contained the 32-bit address of the
list that contains all addresses of the loaded shared libraries. And every
program needed to access that location.

-- 
Derek Parnell
Melbourne, Australia
"Down with mediocrity!"