如何将指向 Python cffi 结构的指针转换为 System.IntPtr (.NET)？

Question

我需要将 System.IntPtr 传递给 .NET 函数（Python with pythonnet）。此指针应引用在 cffi 中创建的结构。

我找到了 this:

from CLR.System import IntPtr, Int32
i = Int32(32)
p = IntPtr.op_Explicit(i)

这是我目前尝试的方法

import clr
from cffi import FFI

ffi = FFI()

custom_t = '''
            typedef struct
            {
                float x;
                 float y;
                 float z;

            } float3;
            '''

ffi.cdef(custom_t)

cfloat3 = ffi.new("float3 *")
cfloat3.x = 1.0
cfloat3.y = 2.0
cfloat3.z = 3.0
print(cfloat3)

from System import IntPtr

p = IntPtr.op_Explicit(id(cfloat3)) #works, sort of...
print(p)

#I would rather see something like
p2 = IntPtr.op_Explicit(ffi.addressof(cfloat3).value)
p3 = IntPtr(ffi.cast("float3*", cfloat3))
p4 = IntPtr(ffi.cast("void3*", cfloat3))

#type(_), ffi.typeof(_), ffi.typeof(_).kind, ffi.addressof()

但我不确定使用 IntPtr.op_Explicit 是否是最佳解决方案。它看起来有点像与 id() 结合使用的解决方法，我很确定有更好的解决方案。

Answer 1

FFI 内置了 addressof 函数：

http://cffi.readthedocs.io/en/latest/ref.html#ffi-addressof

Answer 2

Python.Net 内部不直接支持 CFFI，反之亦然，因此您需要将指针从一个库转换为一个整数，然后将该整数重新导入另一个库。

来自 CFFI，intaddr = ffi.cast("intptr_t", p) 会给你一个整数。那么你可能可以做 IntPtr(intaddr).

Answer 3

解决方法是使用IntPtr

的Overloads方法

from System import IntPtr, Int32, Int64
my_ptr = ffi.cast("intptr_t", my_c_struct)
cs_handle = IntPtr.Overloads[Int64](Int64(int(my_ptr)))

如前所述 and here。

这是一个工作示例：

import clr
from cffi import FFI

ffi = FFI()

custom_t = '''
            typedef struct
            {
                float x;
                 float y;
                 float z;

            } float3;
            '''

ffi.cdef(custom_t)

cfloat3 = ffi.new("float3 *")
cfloat3.x = 1.0
cfloat3.y = 2.0
cfloat3.z = 3.0
print(cfloat3)

from System import IntPtr, Int32, Int64

my_ptr = ffi.cast("intptr_t", cfloat3)
print(my_ptr)
print(ffi.typeof(my_ptr))
print(ffi.typeof(my_ptr).kind)
print(ffi.typeof(my_ptr).cname)
print(int(my_ptr))
print('hex', hex(int(my_ptr)))

#you don't need to cast to System.Int64 first, also works without:

#with casting the Python int to System.Int64
cs_handle = IntPtr.Overloads[Int64](int(my_ptr))
print(cs_handle)

#without casting the Python int to System.Int64
cs_handle = IntPtr.Overloads[Int64](Int64(int(my_ptr)))
print(cs_handle)

# using this workaround mentioned in the question also works
p = IntPtr.op_Explicit(int(my_ptr)) #works, sort of...
print('op_Explicit', p)

#careful: do not use the id() of the C structure, it is different and incorrect
print(cfloat3)
print(ffi.addressof(cfloat3[0]))
print('id(cfloat3)', id(cfloat3), hex(id(cfloat3)))

关于上面发生的事情的一些进一步信息（在这里和那里找到）：

C#'s IntPtr maps exactly to C/C++'s intptr_t.

intptr_t integer type capable of holding a pointer

To cast a pointer to an int, cast it to intptr_t or uintptr_t, which are defined by C to be large enough integer types. cffi doc with examples

IntPtr is just a .NET type for void*.

The equivalent of an unmanaged pointer in the C# language is IntPtr. You can freely convert a pointer back and forth with a cast. No pointer type is associated with it even though its name sounds like "pointer to int", it is the equivalent of void* in C/C++.

IntPtr(5) complains that int/long' value cannot be converted to System.IntPtr. It seems like it is trying to cast or something instead of calling the constructor. (found here)

Methods of CLR objects have an '_ overloads _', which will soon be deprecated in favor of iPy compatible Overloads, attribute that can be used for this purpose. (found here)

如何将指向 Python cffi 结构的指针转换为 System.IntPtr (.NET)？

How to cast a pointer to a Python cffi struct to System.IntPtr (.NET)?

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