SWIG/Examples/ruby/value/

Passing and Returning Structures by Value

Occasionally, a C program will manipulate structures by value such as shown in the following code:

/* File : example.c */

typedef struct Vector {
   double x, y, z;
} Vector;

double dot_product(Vector a, Vector b) {
  return (a.x*b.x + a.y*b.y + a.z*b.z);
}

Vector vector_add(Vector a, Vector b) {
  Vector r;
  r.x = a.x + b.x;
  r.y = a.y + b.y;
  r.z = a.z + b.z;
  return r;
}
Since SWIG only knows how to manage pointers to structures (not their internal representation), the following translations are made when wrappers are created:
double wrap_dot_product(Vector *a, Vector *b) {
    return dot_product(*a,*b);
}

Vector *wrap_vector_add(Vector *a, Vector *b) {
    Vector *r = (Vector *) malloc(sizeof(Vector));
    *r = vector_add(*a,*b);
    return r;
}
The functions are then called using pointers from the scripting language interface. It should also be noted that any function that returns a structure by value results in an implicit memory allocation. This will be a memory leak unless you take steps to free the result (see below).

The SWIG interface

Click here to see a SWIG interface file that wraps these two functions. In this file, there are a few essential features:

A Ruby Script

Click here to see a script that uses these functions from Ruby.

Notes