Re: [Qemu-devel] Coding style, C++ compatible code (was Re: [Qemu-devel] [PATCH 02/22] eepro100: cast a void * makes no sense)

[Avi Kivity <avi@redhat.com>]

On 08/26/2009 04:52 PM, Stefan Weil wrote:
>>> I wrote these type casts, and I think they make sense.
>>> In C++ code, they are even mandatory.
>>>        
>> Yes, but this isn't C++.
>>
>>      
>>> I think the arguments why C++ requires this kind of
>>> type casts apply to C code (like in Qemu) as well.
>>>
>>> If it is possible with no or very litte efforts to write
>>> code which is C and C++ compatible, I prefer to do so.
>>>        
>> I respectfully disagree. Casts from "void *" to "T *" are pure noise.
>> Getting into the habit of writing noise casts runs the risk of silencing
>> warnings that flag real type errors.
>>      
> Hello
>
> Do you only disagree with my first sentence or with both sentences?
>
> Currently, I seem to be alone with my opinion (at least in qemu-devel).
>    

You are not alone.

> Nevertheless, the designers of C++ thought that casts from void * to
> T * were something very important. I don't know the history of their
> decision. I personally think that deriving a data type T from some
> bytes in memory which can contain anything is an operation which is
> worth being documented by the programmer, and this is exactly what
> the cast does.
>    

Yes.

> Let me give one more C/C++ example. Today, many data structures
> are declared like this: typedef struct T { ... } T;
> There is nothing wrong with it, but it can be improved in
> several ways:
>
> * The declaration does not work with C++ (yes, I know that many
>    programmers are not interested in C++ compatibility for QEMU).
>    

It does work in C++.

> * The declaration allows variable declarations using struct T var;
>    or just T var; (which is the QEMU style). I think a declaration
>    which does not enforce the correct style is less good.
>    

It's often needed, for example to have a struct T * in T.


-- 
error compiling committee.c: too many arguments to function