[Rd] Why does an empty vector occupy 40 bytes?
simon.urbanek at r-project.org
Thu Aug 29 16:59:09 CEST 2013
On Aug 29, 2013, at 9:39 AM, Hadley Wickham wrote:
> Hi all,
> Why is the object size of an empty vector 40 bytes? (At least in 64-bit R.)
> # 40 bytes
> Reading R internals, it looks like it should be:
> * 4 bytes: sxpinfo header (= 32 bits)
> * 8 bytes: pointer to attributes
> * 8 bytes: pointer to next node
> * 8 bytes: pointer to previous node
> * 4 bytes: length
> * 4 bytes: true length
> = 36 bytes
> Where are the extra 4 bytes coming from? What have I missed?
Alignment of pointers -- there are 4 bytes of padding on 64-bit machines after sxpinfo
> I thought it might be for memory alignment, but if it was padded by an
> additional 4 bytes, then an integer vector of length 1 should be the
> same size, assuming I've interpreted the comment about "aligned as
> required" correctly.
> Chief Scientist, RStudio
> R-devel at r-project.org mailing list
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