Question

I am trying to add the float values of a ruby array in C with RubyInline (ruby 1.9.2). The expected output should be a float value. Here is my code:

require 'inline'
class ArrayMath

inline :C do |builder|
   builder.c "
        VALUE sum(VALUE arr){

            int size = RARRAY_LEN(arr);
            VALUE *c_arr = RARRAY_PTR(arr);

            int i, x;
            float sum = 0.0;
            for (i=0; i<size; i++)
            {
                x = NUM2DBL(c_arr[i]);
                sum += x;
            }

            return( rb_float_new(sum) );
        }"
   end
end

running this in the console

ArrayMath.new.sum([1,2.7])

outputs 3.0
Obviously the expected result is 3.7

Answer 1

x is an int in your C code. Change that to a float (or double) if you don’t want the result of NUM2DBL truncated.

Or do away with that temporary altogether and write:

sum += NUM2DBL(c_arr[i]);