Hi Tim, On 03/29/2017 08:24 AM, Tim Keitt wrote:
I have a use case where I would like to create an SEXP around an existing buffer that is managed by R, thus avoiding a copy operation.
What to you mean exactly by "an existing buffer managed by R"?
If I have something like: void *p = (void*) RAW(PROTECT(Rf_allocVector(RAWSXP, n))); ... additional maniupulation ... SEXP x = somefunc(SXPTYPE, n, p); // ???? Is there a "placement" constructor available?
What's a "placement" constructor?
(I have arranged for the corresponding UNPROTECT.) I've looked at and experimented with R_allocator and allocVector3, but can't quite get it right. I know this is odd, but it makes sense for my use case.
Not sure I follow what you are trying to do. Note that an SEXP is a pointer to a C struct called SEXPREC. I think that trying to point an
SEXPREC struct to data pointed to by an existing SEXPREC struct is very likely to lead to a disaster. Note that if the existing buffer managed by R is an SEXP (e.g. b) and your code has access to this SEXP then you don't need to create another SEXP around its data. Since SEXPs are pointers doing SEXP x = b; is fine and doesn't generate any copy. And if your code only has access to a "naked" pointer to the buffer managed by R (e.g. to RAW(b) is the buffer is actually in an SEXP) then why would you need to wrap it inside an SEXP? H.
Thanks for any pointers. THK https://urldefense.proofpoint.com/v2/url?u=http-3A__www.keittlab.org_&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=Ceu5dLU_mdGwmpIk_iUqE0dPNjqwy8wiRy6hS_lWF9k&s=h04DJujKDfqzbLz4FmP3_fZ5bYS3t7UEjSwpLrW5mL0&e= [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://urldefense.proofpoint.com/v2/url?u=https-3A__stat.ethz.ch_mailman_listinfo_r-2Ddevel&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=Ceu5dLU_mdGwmpIk_iUqE0dPNjqwy8wiRy6hS_lWF9k&s=WpLxtWWwjoZ7TjW6oW-vxE6s3LY5kZCG1H5h0xb0Bbs&e=
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