Question

I have a structure with different datatype fields. I would like to iterate through the structure fields, check the datatype, and set the field with an appropriate value.

I have access to the size and offset of the field through the .size and .offset attribute of the field. How can I get the ‘type’ attribute of the field? Using type(value) does not print the ctypes datatype for the particular field. If I print value then I do see the ctypes datatype but there doesn’t seem to be an attribute to access this directly.

How can I access the type field descriptor directly?

from ctypes import *

class A(Structure):
    _fields_ = [("one", c_long),
                ("two", c_char),
                ("three", c_byte)]

>>> A.one
<Field type=c_long, ofs=0, size=4>
>>> A.one.offset
0
>>> A.one.size
4
>>> type(A.one)
<class '_ctypes.CField'>

Ideally I would like to get the field type similar to the snippet below…

>>> A.one.type
c_long

Answer 1

Just use the _fields_ list:

>>> for f,t in A._fields_:
...  a = getattr(A,f)
...  print a,a.offset,a.size,t
...
<Field type=c_long, ofs=0, size=4> 0 4 <class 'ctypes.c_long'>
<Field type=c_char, ofs=4, size=1> 4 1 <class 'ctypes.c_char'>
<Field type=c_byte, ofs=5, size=1> 5 1 <class 'ctypes.c_byte'>