Pointers - Is it safe to point to invalid memory?

[Brother Bill]

On Saturday, 16 August 2025 at 15:14:21 UTC, H. S. Teoh wrote:
> On Sat, Aug 16, 2025 at 03:03:21PM +0000, Brother Bill via 
> Digitalmars-d-learn wrote: [...]
>> I'm not sure we are on the same page.
>> My question is whether having a pointer to invalid memory 
>> causes
>> problems.  I am fully aware that reading or writing to an 
>> invalid
>> memory address causes problems.
>> 
>> I am grasping that even having a pointer pointing to an 
>> invalid memory address is a huge code smell.  But will it 
>> cause any undefined behavior merely having a pointer with an 
>> invalid memory address.
>
> What do you mean by "cause any undefined behaviour"?  UB is 
> defined by the language spec, which states that assigning a 
> non-pointer value (or a random garbage value) to a pointer is 
> UB.  What it actually does at runtime is orthogonal to this.  
> At the machine level, there is no UB, it's simply following the 
> instructions you gave it literally.  That the results may not 
> be what you expect is a problem at a higher level of 
> abstraction.
>
>


So a good D developer should not store an invalid pointer address 
into a pointer,
with the single exception of storing a pointer address just past 
a slice or array.