使含有String数组和整数的阵列为C一结构++ DLL(Passing a Structure c

我在与在VB.NET和C ++编组的问题，下面的代码：

在C ++ DLL：

struct APP_PARAM
{
    int numData;
    LPCSTR *text;
    int *values;
};

int App::StartApp(APP_PARAM params)
{
    for (int i = 0; i < numLines; i++)
    {
        OutputDebugString(params.text[i]);
    }
}

在VB.NET：

  <StructLayoutAttribute(LayoutKind.Sequential)> _
  Public Structure APP_PARAM
    Public numData As Integer
    Public text As System.IntPtr
    Public values As System.IntPtr
  End Structure

  Declare Function StartApp Lib "AppSupport.dll" (ByVal params As APP_PARAM) As Integer

  Sub Main()

    Dim params As APP_PARAM
    params.numData = 3

    Dim text As String() = {"A", "B", "C"}
    Dim textHandle As GCHandle = GCHandle.Alloc(text)
    params.text = GCHandle.ToIntPtr(textHandle)

    Dim values As Integer() = {10, 20, 30}
    Dim valuesHandle As GCHandle = GCHandle.Alloc(values)
    params.values = GCHandle.ToIntPtr(heightHandle)

    StartApp(params)

    textHandle.Free()
    valuesHandle.Free()

  End Sub

我检查了C ++侧时，从OutputDebugString的输出是垃圾，文本数组包含随机字符。 什么是这样做的正确方法？

Answer 1:

GCHandle.Alloc “则分配指定的对象正常处理” ，其中“创建一个句柄管理对象......这防止了管理对象被收集”。

什么你要找的是从方法System.Runtime.InteropServices.Marshal ，它允许你做的事情一样复制管理对象由非托管代码访问内存。 不幸的是，根据这个 ，在你的结构指针使它更难一点元帅比许多其他的事情（在这个意义上，许多其他的事情可以使用相应的P为自动编组/ Invoke的属性），但它仍然是可能的。 我已经试过了这一点，它的工作原理：

APP_PARAM param = new APP_PARAM();
string[] text = new string[] { "A", "B", "C" };
param.numData = text.Length;

// Manually allocate an array of pointers, one for each string.  arr holds the array's address.
IntPtr arr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)) * text.Length);
try
{
  param.text = arr;

  IntPtr[] unmanagedText = new IntPtr[text.Length];
  try
  {
    // Create a null-terminated ANSI string in unmanaged memory for each element in text.
    for (int i = 0; i < text.Length; i++)
      unmanagedText[i] = Marshal.StringToHGlobalAnsi(text[i]);
    // Copy the addresses of the unmanaged strings into the manually allocated array.
    // I don't know of any way to make an unmanaged copy of a managed array in one call.
    Marshal.Copy(unmanagedText, 0, arr, unmanagedText.Length);

    // param now looks like what the C++ code is expecting (except for the array of int).
    StartApp(param);
  }
  finally
  {
    foreach (IntPtr str in unmanagedText)
      Marshal.FreeHGlobal(str);
  }
}
finally
{
  Marshal.FreeHGlobal(arr);
}

你必须有类似的分配/你的int类型的数组免费代码，用自己的try / finally块，以确保FreeHGlobal被调用。

Answer 2:

您需要使用从方法之一Marshal类。

Dim str As String = "Hello World"
Dim ptr as IntPtr = Marshal.StringToHGlobalAnsi(str)
Try
  SomePInvokeCall(ptr)
Finally
  Marshal.FreeHGlobal(ptr)
End Try

文章来源: Passing a Structure containing an array of String and an array of Integer into a C++ DLL