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Re: [libvirt] [PATCH v3 1/4] iptablesFormatNetwork(): constify target of "netaddr" parameter



On 09/24/13 10:46, Laine Stump wrote:
> On 09/23/2013 08:03 PM, Laszlo Ersek wrote:
>> ... and adapt functions that would cast away the new const qualifier.
>>
>> Given
>>
>>   typedef virSocketAddr *virSocketAddrPtr;
>>
>> Compare the parse trees of the following two declarations:
>>
>>   (a) const virSocketAddrPtr  addr;
>>   (b) const virSocketAddr    *addr;
> 
> Umm.. Eric? A little help? :-)

The grammar rules that I used for the AST derivation can be looked up
eg. in the final C11 draft,

  http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

Section 6.7 "Declarations".


But, the short version is really just that type qualifiers (like const &
volatile) don't enter the typedef name; they qualify the variable being
declared.

  const virSocketAddrPtr  addr;
  virSocketAddrPtr const  addr;

these are equivalent, they mean the same thing, a constant pointer to a
variable object. Expanding the typedef, that's written as

  virSocketAddr *const addr;

(It is closer in appearance to the second form above.)

If you want to qualify the target of the pointer, you must say one of
the following:

  (i)   const virSocketAddr *addr;

  (ii)  virSocketAddr const *addr;

  (iii) typedef const virSocketAddr *constVirSocketAddrPtr;
        constVirSocketAddrPtr addr;

  (iv) typedef virSocketAddr const *constVirSocketAddrPtr;
       constVirSocketAddrPtr addr;

In general I disapprove of typedefs: they seem to be friendly by saving
you the repeated typing of "struct" and "*". Until they trick you :)

Laszlo


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