Python ctypes.sizeof(...) 总是返回 0

Question

根据我对Python的理解ctypes，ctypes.sizeof(...)应该返回传入结构的大小（以字节为单位），就像使用C的sizeof运算符一样。然而，我总是得到0这样的结果：

$ python
Python 2.7.12 (default, Dec  4 2017, 14:50:18)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes
>>> class testStruct(ctypes.Structure):
...     _fields = [
...         ("testField", ctypes.c_uint*4)
...     ]
...
>>> ctypes.sizeof(testStruct)
0
>>> test = testStruct()
>>> ctypes.sizeof(test)
0

为什么会发生这种情况？

Answer 1

你忘了加下划线_，_fields应该是_fields_。

import ctypes
class testStruct(ctypes.Structure):
    # NOT just _fields:
    _fields_ = [
        ("testField", ctypes.c_uint*4)
    ]

print(ctypes.sizeof(testStruct))
test = testStruct()
print(ctypes.sizeof(test))

输出：

16
16