Question

我尝试通过DLL（由PLC制造商分发的C API接口）与PLC通信。我正在使用Python 3.1作为脚本环境嵌入到其他软件中（x64 - Windows 7）。

我设法让一些DLL函数正常工作，但现在得到了一个“无法解决的访问违规读取”。

有关DLL函数的信息：

LONG AdsSyncReadReq(
  PAmsAddr  pAddr,
  ULONG     nIndexGroup,
  ULONG     nIndexOffset,
  ULONG     nLength,
  PVOID     pData
);

参数：

pAddr：[in]具有NetId和ADS服务器端口号的结构。
nIndexGroup：[in] Index Group。
nIndexOffset：[in] Index Offset。
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

我希望有人无法弄清楚出了什么问题。我只是Python编程方面的高级新手，在C

中完全没有经验

提前致谢

Answer 1

您正在传递无效指针，而是提供有效的内存缓冲区：

data = create_string_buffer(nLength)

如果c_void_p表示POINTER(c_void_p)，则参数应该只是PVOID而不是void *。不要将restype设置为None（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）。

Python Ctypes异常：访问冲突读取

1 个答案: