char *
从用 C 编写的 dll 函数读取 a 时出现问题。
DLL 称为 rapdll.dll。它的头文件看起来像:
extern "C"{void _stdcall New_Rapdll(void);}
extern "C"{void _stdcall TCP_Set_RelayIO(char *Ipaddress,char *SerialNumber,char *Password,char *Data);}
extern "C"{Variant _stdcall Get_Receivedata(void);}
我没有 DLL 的源代码。我遇到问题的命令的帮助文件 (Get_Receivedata()) 是:
宣言
Char * Get_Receivedata(void)
例子:
Get_Receivedata ()
返回值:
See Response from RAP: Success
Data empty: Fail
Description:
This function is getting response from RAP.
到目前为止我写的代码是:
Public Class Form1
Declare Sub TCP_Set_RelayIO Lib "rapdll.dll" (ByVal Ipaddress As String, ByVal Serial As String, ByVal Pass As String, ByVal Relay As String)
Declare Sub TCP_Get_SerialNumber Lib "rapdll.dll" (ByVal Ipaddress As String, ByVal Pass As String)
Declare Sub New_Rapdll Lib "rapdll.dll" ()
Declare Function Get_Receivedata Lib "rapdll.dll" () As String
Dim Result As String
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
Function rap() As String
Result = Get_Receivedata()
Return Result
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim st As String
Call New_Rapdll()
Call TCP_Set_RelayIO("192.168.1.2", "0000", "0000", "00120")
st = rap()
MsgBox(st)
End
End Sub
End Class
一切正常,直到st = rap()行。它之前的命令“Call TCP_Set_RelayIO("192.168.1.2", "0000", "0000", "00120")" 工作正常,因为它确实重置了此设备中的继电器。但是当我尝试使用该Get_Receivedata
函数阅读回复时,我得到了一个“System.AccessViolationException”类型的未处理异常。
我知道问题是试图char *
从函数中读取返回Get_Receivedata
值,但我不确定如何正确执行此操作。
谢谢你的帮助!