在VB.NET中修改C结构

Question

我正在尝试在我的VB.NET应用程序中使用C编码的其他人的DLL。 我的VB.NET应用程序发送一些指向DLL和DLL的回调指针，然后回调我的VB.NET应用程序中的函数。

DLL在VB.NET中调用一个函数并传递一个C结构的指针。 我的VB.NET应用程序必须修改结构值，因此DLL可以使用新的结构值。我不能修改DLL的代码，因为它是别人的DLL。

typedef struct {
  uint8_t index;
  uint8_t value;
  uint8_t leds[4];
  struct {
    int8_t x;
    int8_t y;
    int8_t z;
  } input[10];
} REPORT;

我的VB.NET结构定义是

<StructLayout(LayoutKind.Sequential)> _
Public Structure INPUTS
    Public x As SByte
    Public y As SByte
    Public z As SByte
End Structure

<StructLayout(LayoutKind.Sequential)> _
Public Structure REPORT
    Public index As Byte
    Public value As Byte

    <MarshalAs(UnmanagedType.ByValArray, SizeConst:=4)>
    Public leds() As Byte


    <MarshalAs(UnmanagedType.ByValArray, SizeConst:=10)>
    Public input() As INPUTS

    Sub New(numleds As Integer, numinputs As Integer)
        ReDim Me.leds(numleds)
        ReDim Me.input(numinputs)
    End Sub
End Structure

我的VB.NET委托被声明为

Public Delegate Function Del_Read(ByVal lpReport As IntPtr) As Byte

vb.net将vb.net委托发送给C DLL

Public Ext_Read As Del_Read = New Del_Read(AddressOf Read)
SendToDll(Marshal.GetFunctionPointerForDelegate(Ext_Read))

我的VB.NET函数声明为

 Public Function Read(ByVal lpReport As IntPtr) As Byte

        Dim report As New REPORT(3, 9)

        report.index = 0
        report.value = 5   
        report.input(0).x = 90
        report.input(0).y = 0
        report.input(0).z = 0

        report.input(1).x = 180
        report.input(1).y = 0
        report.input(1).z = 0

        Dim size As Integer = Marshal.SizeOf(report)
        Dim ptrMem As IntPtr = Marshal.AllocCoTaskMem(size)
        Marshal.StructureToPtr(report, ptrMem, False)

        Dim bytes As Byte() = New Byte(size - 1) {}
        Marshal.Copy(ptrMem, bytes, 0, bytes.Length)
        Marshal.FreeCoTaskMem(ptrMem)

        Marshal.Copy(bytes, 0, lpReport, size)

        Return 1
    End Function

当函数结束时，我得到以下错误。

Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

我尝试了不同的代码，例如Marshal.AllocHGlobal或将函数声明为

Public Function Read(ByRef localReport As REPORT) As Byte

即使代码编译得很好，错误也是因为Marshal.StructureToPtr以某种方式，因为如果我将代码更改为如下所示，我没有错误，DLL获得新值。唯一的问题是我必须手动计算report.input(0)，report.input(1)等的偏移量。

Public Function Read(ByVal lpReport As IntPtr) As Byte

    Dim report As New REPORT(3, 9)

    report.index = 0
    report.value = 5

    Dim size As Integer = Marshal.SizeOf(report)
    Dim bytes As Byte() = New Byte(size - 1) {}

    bytes(0) = report.index
    bytes(1) = report.value

    Marshal.Copy(bytes, 0, lpReport, size)

    Return 1
End Function

为什么代码失败的任何想法？或者更简单的方法来修改从DLL发送的结构？