R help - Feb 2005 - Keeping the data of C structure in R variables?..

Dear all,

does anybody know if there is a way to implement the following idea:

if for example I have a C/C++ structure of form:

struct {
    int size;
    char * data;
} SData;

in C code I could create some implementation that would create this 
structure by pointer and fill in the data, so I would have a variable 
something like

SData* myData;

Now what I need is to pass this data to a certain SEXP structure and 
keep it completely in R, thus setting myData = NULL and _unloading the C 
library_; then later I want to create another variable, in another C 
call, SData* myOldData and reload it with values from R. Is there a way 
to do that, keeping also in mind that char* data is generally binary data.

Would be greatful for any suggestions.

Regards
Oleg

I think you should have a look at external pointers (type EXTPTRSXP). They
are used in the R source . See, for example, memory.c. Also see the
developer page notes on weak references, finalizers, etc, which you'll need
to be familiar with. 

This is really an R-devel question!

Reid Huntsinger

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Oleg Sklyar
Sent: Friday, February 04, 2005 11:11 AM
To: R-help@stat.math.ethz.ch
Subject: [R] Keeping the data of C structure in R variables?..


Dear all,

does anybody know if there is a way to implement the following idea:

if for example I have a C/C++ structure of form:

struct {
    int size;
    char * data;
} SData;

in C code I could create some implementation that would create this 
structure by pointer and fill in the data, so I would have a variable 
something like

SData* myData;

Now what I need is to pass this data to a certain SEXP structure and 
keep it completely in R, thus setting myData = NULL and _unloading the C 
library_; then later I want to create another variable, in another C 
call, SData* myOldData and reload it with values from R. Is there a way 
to do that, keeping also in mind that char* data is generally binary data.

Would be greatful for any suggestions.

Regards
Oleg

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