我尝试通过 DLL(PLC 制造商分发的 C API 接口(interface))与 PLC 通信。我正在使用 Python 3.1,它作为脚本环境嵌入到其他软件(x64 - Windows 7)中。
我设法让一些 DLL 函数正常工作,但现在我得到了一个我无法解决的“访问冲突读取”。
DLL函数信息:
LONG AdsSyncReadReq(
PAmsAddr pAddr,
ULONG nIndexGroup,
ULONG nIndexOffset,
ULONG nLength,
PVOID pData
);
参数:
- pAddr:[in] 包含 ADS 服务器的 NetId 和端口号的结构。
- nIndexGroup:[in] 索引组。
- nIndexOffset:[in] 索引偏移量。
- nLength:[in] 数据的字节长度。
- pData:[out] 指向将接收数据的数据缓冲区的指针。
- 返回值:返回函数的错误状态。
结构 AmsAddr:
typedef struct {
AmsNetId netId;
USHORT port;
} AmsAddr, *PAmsAddr;
结构 AmsNetId
typedef struct {
UCHAR b[6];
} AmsNetId, *PAmsNetId;
Python 实现:
# -*- coding: utf-8 -*-
from ctypes import *
#I've tried OleDll and windll as wel..
ADS_DLL = CDLL("C:/Program Files/TwinCAT/Ads Api/TcAdsDll/x64/TcAdsDll.dll")
class AmsNetId(Structure):
_fields_ = [('NetId', c_ubyte*6)]
class AmsAddr(Structure):
_fields_=[('AmsNetId',AmsNetId),('port',c_ushort)]
# DLL function working fine
version = ADS_DLL.AdsGetDllVersion()
print(version)
#DLL function working fine
errCode = ADS_DLL.AdsPortOpen()
print(errCode)
#DLL function using the AmsAddr() class, working fine
amsAddress = AmsAddr()
pointer_amsAddress = pointer(amsAddress)
errCode = ADS_DLL.AdsGetLocalAddress(pointer_amsAddress)
print(errCode)
contents_amsAddres = pointer_amsAddress.contents
#Function that doens't work:
errCode = ADS_DLL.AdsSyncReadReq()
print(errCode) # --> errCode = timeout error, normal because I didn't pass any arguments
# Now with arguments:
plcNetId = AmsNetId((c_ubyte*6)(5,18,18,27,1,1)) #correct adress to the PLC
plcAddress = AmsAddr(plcNetId,801) #correct port to the PLC
nIndexGroup = c_ulong(0xF020)
nIndexOffset = c_ulong(0x0)
nLength = c_ulong(0x4)
data = c_void_p()
pointer_data = pointer(data)
#I tried with an without the following 2 lines, doesn't matters
ADS_DLL.AdsSyncReadReq.argtypes=[AmsAddr,c_ulong,c_ulong,c_ulong,POINTER(c_void_p)]
ADS_DLL.AdsSyncReadReq.restype=None
#This line crashes
errCode = ADS_DLL.AdsSyncReadReq(plcAddress,nIndexGroup,nIndexOffset,nLength,pointer_data)
print(errCode)
>>>> Error in line 57: exception: access violation reading 0xFFFFFFFFFFFFFFFF
我希望任何人都无法弄清楚哪里出了问题。我只是 Python 编程的高级新手,完全没有 C 语言的经验
提前致谢
最佳答案
您传递的是无效指针,请改为提供有效的内存缓冲区:
data = create_string_buffer(nLength)
如果 PVOID
表示 void *
,则参数应该只是 c_void_p
而不是 POINTER(c_void_p)
。不要将 restype 设置为 None
(该函数返回 LONG
)。
同时传递 pointer(plcAddress)
(在 argtypes 中指定 POINTER(AmsAddr)
)。
使用正确的调用约定(在 cdll、windll、oledll 之间选择)。
关于Python Ctypes 异常 : access violation reading,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15472217/