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List:       quagga-dev
Subject:    [quagga-dev 3922] Re: offsetof and buffer.c
From:       Vincent Jardin <vincent.jardin () 6wind ! com>
Date:       2006-01-11 23:40:25
Message-ID: 43C59769.1000207 () 6wind ! com
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Andrew J. Schorr wrote:

>On Wed, Jan 11, 2006 at 11:38:43PM +0100, Vincent Jardin wrote:
>  
>
>>What is it supposed to be the length of this allocated memory ?
>>d = XMALLOC(MTYPE_BUFFER_DATA, offsetof(struct buffer_data, data[b->size]));
>>data[b->size] is not a member of struct buffer_data, but data is such a 
>>member.
>>    
>>
>
>According to <stddef.h>,
>
>   #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
>
>So,
>
>   offsetof(struct buffer_data, data[b->size]) =
>       ((size_t) &((struct buffer_data *)0)->data[b->size])
>
>So, if there are no alignment issues, it's essentially
>equal to: 
>   sizeof(struct buffer_data)+b->size
>
>Does that answer the question?
>  
>
Yes, thanks Andrew.

Regards,
  Vincent

>Regards,
>Andy
>
>  
>

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