python - 如何将指针传递给指向 python 结构的指针数组

Question

我在 Python 中使用 ctypes，我需要将一个指针传递给指向某个 C 函数的结构的指针数组。这是结构:

typedef struct {
    float x;
    float y;
    float z;
    float radius;
} Sphere;

我有以下原型(prototype)的功能:

void render(Sphere** spheres);

在 Python 中，我为 Sphere 结构声明了一个类，我需要将 argtypes 设置为 render 函数:

lib_render = ctypes.cdll.LoadLibrary('librender.so')

class Sphere(ctypes.Structure):
    _fields_ = [('x', ctypes.c_float),
                ('y', ctypes.c_float),
                ('z', ctypes.c_float),
                ('radius', ctypes.c_float)]

render = lib_render.render
render.argtypes = [<cannot find out what needs to be here>]

spheres = numpy.array([Sphere(1, 2.8, 3, 0.5),
                       Sphere(4.2, 2, 1, 3.2)])
render(spheres)

如何正确传递该数组？

Answer 1

我不经常使用 numpy，但没有它，下面的内容也能正常工作。我假设如果您将指针传递给指针，则指针列表必须以 null 结尾。

from ctypes import *

class Sphere(Structure):
    _fields_ = [('x', c_float),
                ('y', c_float),
                ('z', c_float),
                ('radius', c_float)]

dll = CDLL('test')
dll.render.argtypes = POINTER(POINTER(Sphere)),
dll.render.restype = None

# Create a couple of objects
a = Sphere(1,2,3,4)
b = Sphere(5,6,7,8)

# build a list of pointers, null-terminated.
c = (POINTER(Sphere) * 3)(pointer(a),pointer(b),None)
dll.render(c)

测试动态链接库:

#include <stdio.h>

typedef struct Sphere {
    float x;
    float y;
    float z;
    float radius;
} Sphere;

__declspec(dllexport) void render(Sphere** spheres)
{
    for(;*spheres;++spheres)
        printf("%f %f %f %f\n",(*spheres)->x,(*spheres)->y,(*spheres)->z,(*spheres)->radius);
}

输出:

1.000000 2.000000 3.000000 4.000000
5.000000 6.000000 7.000000 8.000000

使用 numpy，使用 void render(Sphere* spheres, size_t len)，这有效。也许更熟悉 numpy 的人可以评论是否可以支持 Sphere**。

from ctypes import *
import numpy as np

class Sphere(Structure):
    _fields_ = [('x', c_float),
                ('y', c_float),
                ('z', c_float),
                ('radius', c_float)]

dll = CDLL('test')
dll.render.argtypes = POINTER(Sphere),c_size_t
dll.render.restype = None

a = Sphere(1,2,3,4)
b = Sphere(5,6,7,8)
# c = (Sphere * 2)(a,b)
# dll.render(c,len(c))
d = np.array([a,b])
dll.render(d.ctypes.data_as(POINTER(Sphere)),len(d))