Glen Rice glen.rice.noaa at gmail.com
Sun Dec 4 09:40:53 EST 2011

• Previous message (by thread): struct calcsize discrepency?
• Next message (by thread): struct calcsize discrepency?
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

---

On Dec 4, 9:38 am, Duncan Booth <duncan.bo... at invalid.invalid> wrote:
> Glen Rice <glen.rice.n... at 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.
>
> Seehttp://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 machine s native format and
> byte order, and properly aligned by skipping pad bytes if necessary
> (according to the rules used by the C compiler)."
>
> --
> Duncan Boothhttp://kupuguy.blogspot.com

Chris / Duncan, Thanks. I missed that in the docs.

---

• Previous message (by thread): struct calcsize discrepency?
• Next message (by thread): struct calcsize discrepency?
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

---

More information about the Python-list mailing list