相当于 "char name [MAX_DEVICE_NAME_LENGTH]" 的 ctypes

Question

在我正在进行的从 python 访问 Digital Persona DLL 函数的测试中，我遇到了以下代码：

import ctypes

# Load DLL into memory.

# dpfpddDll = ctypes.WinDLL ("dpfpdd.dll")
dpfpddDll = ctypes.CDLL ("dpfpdd.dll")


# Library initialization.
dpfpdd_init = dpfpddDll.dpfpdd_init
dpfpdd_init.restype = ctypes.c_int
result = dpfpdd_init()
print(f"Initialize result: {result}")

class dpfpdd_hw_descr_struct(ctypes.Structure):
    _fields_ = [('vendor_name', ctypes.c_char_p),
                ('product_name', ctypes.c_char_p),
                ('serial_num', ctypes.c_char_p)] 

class dpfpdd_hw_id_struct(ctypes.Structure):
     _fields_ = [('vendor_id', ctypes.c_ushort),
                ('product_id', ctypes.c_ushort)] 

class dpfpdd_ver_info_struct(ctypes.Structure):
    _fields_ = [('major', ctypes.c_int),
                ('minor', ctypes.c_int),
                ('maintenance', ctypes.c_int)] 

class dpfpdd_hw_version_struct(ctypes.Structure):
    _fields_ = [('hw_ver', dpfpdd_ver_info_struct),
                ('fw_ver', dpfpdd_ver_info_struct),
                ('bcd_rev', ctypes.c_ushort)]     

class dpfpdd_dev_info_struct(ctypes.Structure):
    _fields_ = [('size', ctypes.c_uint),
                ('name', ctypes.c_char_p),
                ('descr', dpfpdd_hw_descr_struct),
                ('id', dpfpdd_hw_id_struct),
                ('ver', dpfpdd_hw_version_struct),
                ('modality', ctypes.c_uint),
                ('technology', ctypes.c_uint)] 

dpfpdd_query_devices = dpfpddDll.dpfpdd_query_devices

dpfpdd_query_devices.restype = ctypes.c_int

dpfpdd_query_devices.argtypes = [ctypes.POINTER(ctypes.c_uint), ctypes.POINTER(dpfpdd_dev_info_struct)]

p1 = ctypes.c_uint(10)
p2 = dpfpdd_dev_info_struct()
result = dpfpdd_query_devices(ctypes.byref(p1),ctypes.byref(p2))
print("dpfpdd_query_devices result: " + str(result))
print(f"p1: {p1}")
print(f"p2: {p2}")
print(f"p2.size: {p2.size}")
# print(f"p2.name: {p2.name}")
print(f"p2.descr: {p2.descr}")
print(f"p2.id.vendor_id: {p2.id.vendor_id}")
print(f"p2.ver.hw_ver.major: {p2.ver.hw_ver.major}")
print(f"p2.modality: {p2.modality}")
print(f"p2.technology: {p2.technology}")


# Library release.
dpfpdd_exit = dpfpddDll.dpfpdd_exit
dpfpdd_exit.restype = ctypes.c_int
result = dpfpdd_exit()
print(f"Un Initialize result: {result}")

这段代码打印以下内容：

Initialize result: 0
dpfpdd_query_devices result: 0
p1: c_ulong(1)
p2: <__main__.dpfpdd_dev_info_struct object at 0x00000227FB9BAA40>
p2.size: 1452
p2.descr: <__main__.dpfpdd_hw_descr_struct object at 0x00000227FB9BAAC0>
p2.id.vendor_id: 11590
p2.ver.hw_ver.major: 1143816774
p2.modality: 0
p2.technology: 0
Un Initialize result: 0

似乎调用成功了，因为我能够从返回的参数 p2 中读取一些字段，但是一旦我取消注释这一行：

print(f"p2.name: {p2.name}")

我只打印了这个：

Initialize result: 0
dpfpdd_query_devices result: 0
p1: c_ulong(1)
p2: <__main__.dpfpdd_dev_info_struct object at 0x00000228B0419A40>
p2.size: 1452

所以似乎访问 p2.name 在 python 中引起了问题并导致停止！

我在 class dpfpdd_dev_info_struct 中对字段“名称”的声明是否正确？

('name', ctypes.c_char_p)

此字段在 SDK Headers 中定义为：

#define     MAX_DEVICE_NAME_LENGTH   1024
char    name [MAX_DEVICE_NAME_LENGTH]

感谢任何帮助。

谢谢。

Answer 1

我通过像这样声明名称变量来让它工作：

('name', ctypes.c_char * 1024)

相当于 "char name [MAX_DEVICE_NAME_LENGTH]" 的 ctypes

ctypes equivalent of "char name [MAX_DEVICE_NAME_LENGTH]"

python

ctypes

digital-persona-sdk