调用简单的C++函数

要在C#代码中调用C++函数，大体的思路是这样的：首先将C++函数写成DLL形式的库，然后在C#中导入DLL中的函数进行调用。具体的代码类似这样：

int StaticElementNumber = 10;  extern "C" AFX_API_EXPORT int GetArrayElementNumber() {         return StaticElementNumber; }

C#代码：

[DllImport("MFCDll.dll")]public static extern int GetArrayElementNumber();int ElementNumber = GetArrayElementNumber();

s其中的细节，比如int和char等数据类型在C++和C#中占用的空间不同等等CLR会自动处理。(主要是通过Marshal类自动处理)

这样的调用还支持调试。打开C#工程的Properties，在Debug选项卡中勾选Enable unmanaged code debugging即可启用C++代码调试。这样在调试模式下，调用这个函数时可以继续按F11跟进函数内部进行调试。

传递GDI对象

一些复杂的Windows对象可以通过句柄来传送。比如下面的代码就将一个GDI+ Bitmap对象转换成GDI句柄进行传送。

extern "C" AFX_API_EXPORT HBITMAP GetABitmap(WCHAR *strFileName) {          Gdiplus::GdiplusStartupInput gdiplusStartupInput;          ULONG_PTR           gdiplusToken;          GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);          Bitmap *bitmap = Bitmap::FromFile(strFileName);          HBITMAP HBitmapToReturn;          bitmap->GetHBITMAP(NULL, &HBitmapToReturn);          GdiplusShutdown(gdiplusToken);           return HBitmapToReturn; }

C#代码(用户界面采用WPF，略去相关声明和引用)：

[DllImport("MFCDll.dll")]   public static extern IntPtr GetABitmap([MarshalAs(UnmanagedType.LPWStr)] string strFileName);     private void MenuItemFileOpenOnClicked(object sender, RoutedEventArgs e)  {      OpenFileDialog dialog = new OpenFileDialog();      dialog.Title = "Load an image...";      dialog.Multiselect = false;      if (dialog.ShowDialog() == true)     {         mainGrid.Children.Clear();           IntPtr hBitmap = GetABitmap(dialog.FileName);         Bitmap bitmap = Bitmap.FromHbitmap(hBitmap);         System.Windows.Controls.Image image = new Windows.Controls.Image();         image.Source = Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(hBitmap, ro, Int32Rect.Empty,         Windows.Media.Imaging.BitmapSizeOptions.FromEmptyOptions());         image.Stretch = System.Windows.Media.Stretch.Fill;         DeleteObject(hBitmap);         mainGrid.Children.Add(image);     } }

传递数组

传递定长数组很简单，此处不述。下面的代码实现变长数组的传递：

int StaticElementNumber = 10;  extern "C" AFX_API_EXPORT bool GetArray(int ElementNumber, double *BaseAddress)  {      if (ElementNumber < StaticElementNumber)      {          return false;      }         for (int i = 0; i < StaticElementNumber; ++i)     {         BaseAddress[i] = 1 / ((double)i + 1);     }       return true; }   extern "C" AFX_API_EXPORT int GetArrayElementNumber() {     return StaticElementNumber; }

C#代码：

[DllImport("MFCDll.dll")]  public static extern bool GetArray(int ElementNumber, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 0)] double[] BaseAddress);    private void MenuItemFileGetArrayOnClicked(object sender, RoutedEventArgs e)  {      //Get array data.      int ElementNumber = GetArrayElementNumber();      double[] doubleArray = new double[ElementNumber];      GetArray(ElementNumber, doubleArray);       //Show the data.     mainGrid.Children.Clear();     ListBox listBox = new ListBox();     foreach (double number in doubleArray)     {         listBox.Items.Add(number);     }     mainGrid.Children.Add(listBox); }