Node-ffi example: Passing and receiving array object between Node.js and C++ binding

index.js

var repl = require('repl');
var ffi = require('ffi');
var ref = require('ref');
var ArrayType = require('ref-array');
var int = ref.types.int;
var IntArray = ArrayType(int);

var lib = ffi.Library('mylib', {
  'createMatrix': [IntArray, [int, IntArray, int] ]
});

var a = [0, 1, 2, 3, 4];
var array = new IntArray(a);

var result = lib.createMatrix(100, array, array.length);
repl.start('> ').context.r = result;

main.cpp

#include <iostream>
#include <armadillo>

using namespace std;
using namespace arma;

extern "C" {

  int *createMatrix(int n, int arr[], int size) {
    sp_mat A = zeros<sp_mat>(n, n);
    sp_mat B = zeros<sp_mat>(n, n);
    for (int i =0; i<size; ++i) {
      A(i, i) = arr[i]+1;
      B(i, i) = arr[i];
    }
    sp_mat C = A*B;
    cout << C.t() << endl;
    for (int i=0; i< size; ++i) {
      arr[i] = C(i, i);
    }
    return arr;
  }

}

Node-ffi-array.md

Node-ffi with IntArray

Passing and receiving array object between Node.js and C++ binding

$ g++ -dynamiclib -o mylib.dylib main.cpp
$ node index.js
[matrix size: 100x100; n_nonzero: 4; density: 0.04%]

     (1, 1)          2.0000
     (2, 2)          6.0000
     (3, 3)         12.0000
     (4, 4)         20.0000


> r
[ buffer: <Buffer@0x102805568 > ]
> r[0]
0
> r[1]
2
> r[2]
6
> r[3]
12
> r[4]
20
>