Re: [NtDev] Re: Silly question on IA64

NTDEV
1

antognini@us.ibm.com said:

Sorry, I disagree with your assertion that only a pointer variable
should hold a pointer. I am continually doing pointer arithmetic, and
I have to cast a pointer into what works, typically a ULONG.

Why? Arithmetic on pointers is well defined in C.

And if you argue that you want per-byte resolution, then cast your
pointer into an ``unsigned char*‘’ instead of an unsigned long. There
are types available within the language to portably to what you want.

antognini@us.ibm.com said:

Interestingly, the macro CONTAINING_RECORD64 does arithmetic on
ULONGLONG, which is not a pointer type. You may say Microsoft ought to
have defined a ULONGLONG_PTR type to kept things pure, but I feel
doing so or not doing so is a matter of taste.

Perhaps I’m letting my bias show here, but I can’t imagine using MS
code as a model of good programming style. At least not the examples
available to us outsiders.

Steve Williams “The woods are lovely, dark and deep.
xxxxx@icarus.com But I have promises to keep,
xxxxx@picturel.com and lines to code before I sleep,
http://www.picturel.com And lines to code before I sleep.”

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2

This is not a rhetorical question, I really don’t know the answer, although
I have my suspicions of what the answer should be…

What is the difference between casting to a ULONG, and casting to a PVOID?
If you ++ either one, they both increment by one. If you add 0x10, they
will both advance by 16. So why is ULONG, which isn’t 100% safe, preferred
over PVOID, which is? Are there issues using PVOID that don’t show up using
ULONG?

Thanks,

Phil

-----Original Message-----
From: James Antognini [mailto:antognini@us.ibm.com]
Sent: Wednesday, June 06, 2001 8:08 AM
To: NT Developers Interest List
Subject: [ntdev] Re: [NtDev] Re: Silly question on IA64

Sorry, I disagree with your assertion that only a pointer variable
should hold a pointer. I am continually doing pointer arithmetic, and I
have to cast a pointer into what works, typically a ULONG.
Interestingly, the macro CONTAINING_RECORD64 does arithmetic on
ULONGLONG, which is not a pointer type. You may say Microsoft ought to
have defined a ULONGLONG_PTR type to kept things pure, but I feel doing
so or not doing so is a matter of taste.

That said, in product code where I used ULONG for pointer values, I
always appended a comment that the technique was not
64-bit-address-safe. Matters of taste aside, it’s wise to leave a
warning.

–
James Antognini
IBM Watson Research

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3

Doesn’t PVOID present a problem in that its increment value is
undefined? Perhaps you meant PCHAR (or PBYTE), which does increment by
1.

–
James Antognini
IBM Watson Research

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4

To answer your question substantively, I’ve run into cases where PCHAR
didn’t work the way I needed. I’ll try to find some of them.

–
James Antognini
IBM Watson Research

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