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我尝试通过DLL(由PLC制造商分发的C API接口)与PLC通信。我使用Python 3.1作为脚本环境嵌入到其他软件(x64 - Windows 7)中。Python Ctypes异常:访问违规读取
我设法得到一些DLL函数的工作,但现在得到一个“访问冲突阅读”,我无法解决。
对DLL功能的信息:
LONG AdsSyncReadReq(
PAmsAddr pAddr,
ULONG nIndexGroup,
ULONG nIndexOffset,
ULONG nLength,
PVOID pData
);
参数:
- PADDR:[中]与NETID和ADS服务器的端口号结构。
- nIndexGroup:[in]索引组。
- nIndexOffset:[in]索引偏移量。
- nLength:[in]以字节为单位的数据长度。
- 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什么是错的。我只是在Python编程没有任何经验,在C中的全部先进新手提前
感谢
我试过你的解决方案,但它没有奏效。我仍然收到相同的错误信息。我想这个问题在第一个参数(plcAddress)中。 'errCode = ADS_DLL.AdsSyncReadReq(plcAddress)' 给出了相同的错误 – 2013-03-18 09:30:00
我已经更新了答案:使用'pointer(plcAddress)'。 – jfs 2013-03-18 09:33:50
非常感谢。错误信息消失了。我仍然没有从PLC那里得到我想要的回应,但那是另一回事.... :-) – 2013-03-18 09:41:33