[Rd] Calling an array in a struct in C to R

Tee-Jay-Ardie tjardie at gmail.com
Wed Jun 19 16:14:40 CEST 2013

Hi there,

Although I'm a quite experienced R user and know my ways in C, I stumbled
upon a problem I don't know how to solve. Therefore, I hope someone can
provide me with the information or pointers I need in order to understand
the way in which the communication between R and C occurs. I have the
following C code which basicallly reflects what I want:

typedef struct
       float *array;
       size_t used;
       size_t size;
} Array;

void main2R()
      Array a;
      examplefunction(&a);   /*fills and dynamically grows a->array*/

Now I would want to return a.array or a->array to R. According to the R
manuals, the compiled C code should not return anything except through its
arguments. The problem here is, I have a dynamically growing array, and I
have no idea what to pass on to C from R in order to let that work. 
The word 'should' indicates that the compiled code may return something in
special circumstances, but I have no idea how to get a.array in R. 

So my question is simply this: How on earth do I get the information in the
float array 'a.array' in R? Is it even possible or should I rewrite my C
code using Call in R? 

Another, not preferred, options is to pre-allocate the array/vector in R on
a fixed (large-enough) size? Or do I miss something here? 


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