[cfe-dev] sizeof (RopeRefCountString)

[Daniel Dunbar]

#include <stddef.h>

unsigned AllocSize = sizeof(RopeRefCountString) -
offsetof(RopeRefCountString,Data) + AllocChunkSize;

On Mon, Sep 15, 2008 at 9:22 PM, Ted Kremenek <kremenek at apple.com> wrote:
>
> On Sep 15, 2008, at 6:35 PM, Zhongxing Xu wrote:
>
>
> 2008/9/16 Ted Kremenek <kremenek at apple.com>
>>
>> On Sep 7, 2008, at 1:32 AM, Zhongxing Xu wrote:
>>
>>> Hi,
>>>
>>> In RewriteRope.cpp, RewriteRope::MakeRopeString(const char *Start, const
>>> char *End),
>>> we calculate the AllocSize by:
>>>
>>> unsigned AllocSize = sizeof(RopeRefCountString) - 1 + AllocChunkSize;
>>>
>>> I guess here the intention is: sizeof(RopeRefCountString) is 5. But gcc
>>> says sizeof(RopeRefCountString) is 8. So the actual AllocSize is 4087.
>>> Should we minus 4 instead of 1 to make the AllocSize 4084?
>>
>> The "-1" I believe is to accommodate for the field Data[1], which occupies
>> a single byte:
>
> In practice it occupies 4 bytes because of tail padding.
>
> Right.  Isn't there a pointer arithmetic trick we can do here to get the
> right number?
>
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