[Rd] NUMERIC_POINTER question

[Huntsinger, Reid]

You have to coerce to numeric yourself if that's what you want. Eg in the R
code, as.numeric(1:12) rather than 1:12. Or check the type first in C with
TYPEOF before doing NUMERIC_POINTER or INTEGER_POINTER (the difference is
that the two do different casts; they both point a fixed offset into the R
data structure and I'm not sure if there's a guarantee that this offset
needs to be the same, so perhaps the two don't even point to the same
location...).

Reid Huntsinger

-----Original Message-----
From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-project.org]
On Behalf Of nwew
Sent: Tuesday, September 13, 2005 2:26 PM
To: r-devel
Subject: [Rd] NUMERIC_POINTER question


Dear R-developers,

Using .Call I pass a S4 class with e.g. the following class definition:

setClass("mmatrix",representation(
   data="matrix")
)

On the "C side" i do
mat = GET_SLOT(vs,install("data"));
and then:
printf("%f\n",NUMERIC_POINTER(mat)[1]);


The above print statement produces the correct output if 
xx<- new("mmatrix")
xx at data<-matrix(1:12+0.1,3,4). (data is double)

However it prints 
0.0000 
if xx at data are integers ( xx at data<-matrix(1:12,3,4) ).

Can anyone explain it to me why? 
I thought that NUMERIC_POINTER makes it clear that i expect datatype
numeric.
(Why otherwise the distinction with INTEGER_POINTER)


cheers
Eryk

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