Glen Rice <glen.rice.n...@gmail.com> wrote:
> In IPython:
>>import struct
>>struct.calcsize('4s')
> 4
>>struct.calcsize('Q')
> 8
>>struct.calcsize('4sQ')
> 16
>
> This doesn't make sense to me. Can anyone explain?
>
When you mix different types in a struct there can be padding inserted
between the items. In this case the 8 byte unsigned long long must always
start on an 8 byte boundary so 4 padding bytes are inserted.
See http://docs.python.org/library/struct.html?highlight=struct#byte-order-
size-and-alignment in particular the first sentence:
"By default, C types are represented in the machines native format and
byte order, and properly aligned by skipping pad bytes if necessary
(according to the rules used by the C compiler)."
--
Duncan Booth http://kupuguy.blogspot.com
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