问题
I need to pass a System.IntPtr to a .NET function (Python with pythonnet). This pointer should refer to a struct created in cffi.
I found this:
from CLR.System import IntPtr, Int32
i = Int32(32)
p = IntPtr.op_Explicit(i)
This is what I tried so far
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()
But I am not sure if using IntPtr.op_Explicit is the best solution. It looks a bit like workaround in combination with id() and I am pretty sure there is a better solution.
回答1:
There is no direct support for CFFI inside Python.Net or vice-versa, so you need to cast the pointer from one library to an integer and reimport that integer into the other library.
From CFFI, intaddr = ffi.cast("intptr_t", p) will give you an integer. Then you can probably do IntPtr(intaddr).
回答2:
FFI has an addressof function built in:
http://cffi.readthedocs.io/en/latest/ref.html#ffi-addressof
回答3:
The solution to this is to use the Overloads method of IntPtr
from System import IntPtr, Int32, Int64
my_ptr = ffi.cast("intptr_t", my_c_struct)
cs_handle = IntPtr.Overloads[Int64](Int64(int(my_ptr)))
as mentioned here and here.
Here is a working example:
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)))
Some further info on what is happening above (found here and there):
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)
来源：https://stackoverflow.com/questions/45860493/how-to-cast-a-pointer-to-a-python-cffi-struct-to-system-intptr-net