Re: [9fans] void*

[Humm <hummsmith42@gmail.com>]

>one of the first thing I noticed compiling in plan9 is that arithmetic 
>on void* is illegal.

That’s what the standard says.

While Plan 9 C doesn’t pretend to be compliant, the core language does 
roughly match C89 with a few C99 extensions.

>Other compilers treat void* as uchar*. Conceptually, it  makes sense. 
>A pointer to void doesn't point to any object. But then I've seen the 
>use of void* in functions (like memccpy) when the pointed object is 
>going to be processed as a byte array. Local uchar*'s are used to do 
>the trick inside the function.
>
>It wouldn't make more sense to avoid the use of void* and just use 
>instead uchar* or better still u8int*?

(Those are different.  On Plan 9, we do make (too many) assumptions 
about type sizes, but conceptually, a byte need not be limited to eight 
bit.)

I’m now quoting the C99 Rationale (revision 5.10).

Page 37, § 6.2.5:

>A pointer to void must have the same representation and alignment as 
>a pointer to char; the intent of this rule is to allow existing 
>programs that call library functions such as memcpy and free to 
>continue to work.

Page 48, § 6.3.2.3:

>The use of void* (“pointer to void”) as a generic object pointer type 
>is an invention of the C89 Committee.  Adoption of this type was 
>stimulated by the desire to specify function prototype arguments that 
>either quietly convert arbitrary pointers (as in fread) or complain if 
>the argument type does not exactly match (as in strcmp).

-- 
Humm

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