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From: "Bo Persson" <bop@gmb.dk>
Subject: Re: To standardize Boost.Pool
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Phil Bouchard wrote:
> On 4/14/2011 12:10 PM, Phil Bouchard wrote:
>
>>
>> is_from() actually invokes undefined behavior if its parameter is a
>> pointer referring to an element outside of the pool according to
>> 5.7.6. If the pointer was to be casted to the largest integer type
>> available on the system then a range check would be valid for that
>> system.
>> For example:
>>
>> bool is_from(const char* p)
>> {
>> return reinterpret_cast<long>(buffer)<= reinterpret_cast<long>(p)&&
>> reinterpret_cast<long>(p)< reinterpret_cast<long>(buffer +
>> sizeof(buffer)); }
>>
>> It's "implementation defined" but perhaps a reinterpret_cast of a
>> pointer to a long integer could be guaranteed to be valid by the
>> standards, long being the greatest integer available on a system.
>>
>
> It turns out the C standard defines intptr_t to be the same size as
> a pointer (7.18.1.4).  The following would consequently be
> perfectly portable:
> bool is_from(const char* p)
> {
>   return reinterpret_cast<intptr_t>(buffer)<=
> reinterpret_cast<intptr_t>(p)&&
> reinterpret_cast<intptr_t>(p)< reinterpret_cast<intptr_t>(buffer +
> sizeof(buffer));
> }
>
>

For some definition of "perfectly", yes.

The typedef is optional, because there is no requirement for an
implementation to actually have an integer type wide enough to hold a
pointer.


Bo Persson



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