[Info-vax] problem with 64-bit pointers in C

[Joukj]

Jan-Erik Soderholm wrote:
> Den 2018-01-31 kl. 11:08, skrev Joukj:
>> ergamenes at gmail.com wrote:
>>> On Wednesday, 31 January 2018 08:36:25 UTC, Joukj  wrote:
>>>
>>>> Looks like the artthmatic - (and + ) on pointers is not resulting in 
>>>> the expected 64-bit pointer as it should.
>>>
>>> I can see two problems: one is that subtracting arbitrary pointers is 
>>> UB, so anything can happen.
>> The code where it comes from uses this to determine the length a 
>> data-string. It works OK with 32 bit pointers.
>>
>>>
>>> The other thing is that when it is valid, it gives a result that is 
>>> of type ptrdiff_t, which here is defined to be an int. That does mean 
>>> that there is a restriction that you can't have arrays of more than 
>>> 2^31 elements. 
>>
>> What I read from the error message is that the subtraction is 
>> performed in 64 bit but afterwards the result is cast to a int (or 
>> prtdiff_t). What is the reason for doing this?
>> If I run my sample program on a 64-bit Linux system I get the expected 
>> results.
>>
>>                  Jouk
> 
> http://www.gnu.org/software/libc/manual/html_node/Important-Data-Types.html
> 
> 
This implicates that when compiling with 64-bit pointers you always get 
a warning when subtracting pointers with DECC. How can you avoid the 
warning!

          Jouk