将Ctypes数组的一部分转换为结构

Question

I have a big long ctypes array of about 500K uint_32s. I want a section from arr[0x4000] to arr[0x8000] to be referenced in a ctypes structure.

Basically:

class my_struct(Structure):
    _fields_ = [
        (important_thing, c_uint32*128),
        (other_thing, c_uint32*16) #etc. etc.
    ]

#arr is a huge ctypes array of length 500K made up of uint_32
section1 = cast(addressof(arr[0x4000:0x8000]),POINTER(my_struct)

However, doing arr[a,b] turns it from a ctype array to a python list, and I therefore can't use addressof.

I'm doing it this way becuase I want to be able to do something like:

section1.important_thing = 0x12345

and for it to change the raw data in the list, but I don't know exactly how.

Thanks for your help.

Answer 1

[Python 3.Docs]: ctypes - from_buffer ( source[, offset] ) is what you're looking for.

Example :

 >>> import ctypes >>> >>> class Struct0(ctypes.Structure): ... _fields_ = [ ... ("important", ctypes.c_uint32 * 128), ... ("other", ctypes.c_uint32 * 16), # Other fields ... ] ... >>> >>> arr = (ctypes.c_uint32 * 0x200)(*range(0x0200)) # Array filled with values [0 .. 511] >>> arr[0x0001], arr[0x0100], arr[0x01FF] (1, 256, 511) >>> >>> s0 = Struct0.from_buffer(arr, 0x0100 * ctypes.sizeof(ctypes.c_uint32)) # Start from 257th element (index 256) >>> >>> s0.important[0x0000], s0.important[0x007F] # Struct0.important first and last elements (256, 383)