Question

我在Python中使用ctypes，我需要将一个指向数组指针的指针传递给一些C函数。这是结构：

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

我可以使用以下原型：

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

我不会使用numpy，但是如果没有它，后续工作。我假设您是否传递指针指针，指针列表必须以空值终止。

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DLL：

#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。如果可以支持Sphere**，也许更熟悉numpy的人可以发表评论。

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))

如何将指针传递给指向python结构的指针数组

1 个答案: