使用 Cython 包装 C++ 类时处理指针

Question

I'm having trouble when handling pointers with cython. The cython implementation of the class holds a pointer to a C++ instance of class Person . Here's my .pyx file:

person.pyx

cdef class PyPerson:
    cdef Person *pointer

    def __cinit__(self):
        self.pointer=new Person()

    def set_parent(self, PyPerson father):
        cdef Person new_father=*(father.pointer)
        self.c_person.setParent(new_father)        

The C++ method setParent takes a Person object as an argument. Since the attribute pointer of the PyPerson class is a pointer to a Person object, I thought that I could get the object at the adress pointed by *pointer with the syntax *(PyPersonObject.pointer) . However when I try to compile it I get the following error

 def set_parent(self, PyPerson father):
    cdef Person new_father=*(father.pointer)
                             ^
------------------------------------------------------------

person.pyx:51:30: Cannot assign type 'Person *' to 'Person'

Does someone knows how can I get to the object at the adress of the pointer? When I do the same in a C++ program I get no error. Here's the implementation of the C++ class in case you want to see it :

person.cpp

Person::Person():parent(NULL){
}

Person::setParent(Person &p){
     parent=&p;
}

NOTE: I can't solve it by holding a Person instance ( cdef Peron not_pointer ) for other reasons involving the complete class.

Answer 1

I should have read the entire cython docs on using C++ with Cython. For those who don't know, the dereference operator * can't be used in Cython. Instead you need to import dereference from the cython.operator module. When you want to access the object at the pointed address, you should write dereference(pointer) .

In concrete, the answer to my problem is to write cdef Person new_father=dereference(father.c_person) .

Answer 2

One another solution to this might be to index into the pointer at location 0 to dereference a pointer in Cython. For example, suppose we have a golden_ratio C double and a p_double C pointer:

cdef double golden_ratio
cdef double *p_double

We can assign golden_ratio's address to p_double using the address-of operator, &:

p_double = &golden_ratio

We can now assign to golden_ratio through p_double using our indexing-at-zero-to-dereference syntax:

p_double[0] = 1.618
print(golden_ratio)
# => 1.618