调用具有“指针”和结构的DLL（C ++-> VB.NET）

Question

I have problem about how I call a function on DLL to get data from a structure ...

Have a C++ example about how it's works the library, and I want to use it on vb.net

Okay, this is the working c++ example:

Declaration:

BOOL (WINAPIV* MyFun)(DWORD start1, DWORD stop1, P_RESULT pResult, PDWORD pTpNum, myCALLBACK lpFunc) = NULL;

Call:

// pStruc = RESULT structure
// TrpNum1, TrpNum is ULONG

ULONG TrpNum1=0;
MyFun(Start,Stop,pStruc+TrpNum,&TrpNum1,&myCB);

Callback:

void __stdcall myCB (RESULT *pStruc)
{
    printf ("%.3f", (double)pStruc->val1);
    tpn++;
}

And of course, the structure:

typedef struct {
    BOOL            mybool;
    DWORD           val1;       
    DWORD           val2;       
} RESULT, *P_RESULT;

And this is my VB.net code (not working):

Public Declare Auto Function MyFun Lib "\mydll.dll" ( _
        ByVal start As UInt32, _
        ByVal stop As UInt32, _
        ByRef Result As RESULT, ByRef pTpNum As UInt32, ByVal lpFunc As DlgCB) As Boolean

Public Sub CallMyFun()
    Dim Res As New RESULT
    Dim TpN As UInt32

    If MyFun(100, 200, Res, TpN, AddressOf myCB) Then
        SendDebug("OK")

    Else
        SendDebug("Failed!")
    End If

End Sub

Public Delegate Function DlgCB(ByVal Res As RESULT) As Boolean

Public Function myCB(ByVal Res As RESULT) As Boolean
    Debug.Print(Res.val1)
    Return True
End Function

Structure:

Public Structure RESULT
    Dim mybool As Boolean
    Dim val1 As UInt32
    Dim val2 As UInt32
End Structure

What is wrong guys?

Thanks in advance.

Edit: The error is this: "Attempted to read or write protected memory. This often indicates that other memory is corrupt."

Also i do a small 'fix' in the code. Still don't work.

Answer 1

There are a large number of problems here:

• myBool is an Integer, not a Boolean
• the Res variable almost surely can't be a local variable, make it a field
• possibly the same for TpN, it isn't clear if the C++ code stores the pointer
• for both, if the C++ code stores a pointer then the object needs to be pinned. Marshaling yourself to memory allocated with Marshal.AllocHGlobal is much better
• the delegate you create with AddressOf is going to get garbage collected. You need to store a reference in a field so that can't happen
• the callback should declare the parameter ByRef, not ByVal
• the C++ callback is void, you made it return a Boolean for some reason.

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