在C扩展模块中操作隐形指针

隐形结构体可以很容易的通过将它们包装在胶囊对象中来处理。 考虑我们例子代码中的下列C代码片段：

typedef struct Point {
    double x,y;
} Point;

extern double distance(Point *p1, Point *p2);
下面是一个使用胶囊包装Point结构体和 distance() 函数的扩展代码实例：

/* Destructor function for points */
static void del_Point(PyObject *obj) {
  free(PyCapsule_GetPointer(obj,"Point"));
}

/* Utility functions */
static Point *PyPoint_AsPoint(PyObject *obj) {
  return (Point *) PyCapsule_GetPointer(obj, "Point");
}

static PyObject *PyPoint_FromPoint(Point *p, int must_free) {
  return PyCapsule_New(p, "Point", must_free ? del_Point : NULL);
}

/* Create a new Point object */
static PyObject *py_Point(PyObject *self, PyObject *args) {

  Point *p;
  double x,y;
  if (!PyArg_ParseTuple(args,"dd",&x,&y)) {
    return NULL;
  }
  p = (Point *) malloc(sizeof(Point));
  p->x = x;
  p->y = y;
  return PyPoint_FromPoint(p, 1);
}

static PyObject *py_distance(PyObject *self, PyObject *args) {
  Point *p1, *p2;
  PyObject *py_p1, *py_p2;
  double result;

  if (!PyArg_ParseTuple(args,"OO",&py_p1, &py_p2)) {
    return NULL;
  }
  if (!(p1 = PyPoint_AsPoint(py_p1))) {
    return NULL;
  }
  if (!(p2 = PyPoint_AsPoint(py_p2))) {
    return NULL;
  }
  result = distance(p1,p2);
  return Py_BuildValue("d", result);
}
在Python中可以像下面这样来使用这些函数：

>>> import sample
>>> p1 = sample.Point(2,3)
>>> p2 = sample.Point(4,5)
>>> p1
<capsule object "Point" at 0x1004ea330>
>>> p2
<capsule object "Point" at 0x1005d1db0>
>>> sample.distance(p1,p2)
2.8284271247461903
>>>