I have an 'n' Byte bytearray. This is same as one of the defined ctypes.Sturcture. I want to typecast this bytearray to this sturcture. so that I can access each of this member. How can I do that?
class ABC(Structure):
_fields_ = [("a", c_uint), ("b", c_ushort), ("c", c_ushort)]
class DEF(Structure):
_fields_ = [("abc", ABC), ("i", I)]
b = bytearray(b'\x88\x08\xc0\xf9\x02\x85\x10\x00\xcc')
s = DEF()
print(s.abc.a)
How do I get the the correct value of the above print
statement?
You can use from_buffer
on the desired type (rather than the object instance):
from ctypes import Structure, c_uint, c_ushort, c_uint8
class ABC(Structure):
_pack_ = 1
_fields_ = [("a", c_uint), ("b", c_ushort), ("c", c_ushort)]
class DEF(Structure):
_pack_ = 1
_fields_ = [("abc", ABC), ("i", c_uint8)]
def main():
b = bytearray(b'\x88\x08\xc0\xf9\x02\x85\x10\x00\xcc')
# check if bytearray can be applied to structure.
if len(b) < ctypes.sizeof(DEF):
print("error: bytearray is too short for DEF.")
return
s = DEF.from_buffer(b)
print("abc.a: {:#x}".format(s.abc.a))
print("abc.b: {:#x}".format(s.abc.b))
print("abc.c: {:#x}".format(s.abc.c))
print("i: {:#x}".format(s.i))
if __name__ == '__main__':
main()
Note that the structure must be packed accordingly, thus I used a _pack_ = 1
so the expected size of DEF
structure is 9 bytes (4 + 2 + 2 + 1) rather than 12.
I also used c_uint8
for the DEF.i
field as this is probably what you meant (I
, in your example, is not a type).
Output:
abc.a: 0xf9c00888
abc.b: 0x8502
abc.c: 0x10
i: 0xcc
If you want the value in big endian (rather than the default little endian), change the endianness of the structure by using ctypes.BigEndianStructure
.
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