C#调用C++写的dll的问题，也许对熟悉的人很简单，但是这个问题我查了很多资料也没解决

Question

c++中 有这样的方法
DWORD GetChallenge(IN HANDLE hContext,
                     IN WCHAR  *pszUserName,
                     OUT BYTE  **pChallenge, 
                     OUT DWORD *dwcbChallenge);
C#中我用下面的方法使用
[DllImport("cardmgr.DLL", SetLastError = true)]
        public static extern uint CMGetChallenge
            (
            IntPtr hContext,
            [MarshalAs(UnmanagedType.LPWStr)] string pwszUserName,
            ref byte[] pbChallenge,
            ref int cbChallenge);但是在 程序中运行时获取的pbChallenge不正确，以下是调用代码
 uint dwAcquireCardStatus = 1;
            uint dwLockCardStatus = 1;
            uint dwChangePinStatus = 0;
            IntPtr hContext = new IntPtr();
            int lenChallenge = 16;
            byte[] challenge = new byte[16];            dwAcquireCardStatus = CardMgrWrapper.CCAcquireSingleCard(ref hContext);
            if (dwAcquireCardStatus == 0)
            {
                dwLockCardStatus = CardMgrWrapper.CCLockCard(hContext, 0);
                if (dwLockCardStatus == 0)
                {
                    dwChangePinStatus = CardMgrWrapper.CMGetChallenge2(hContext,
                                                             SCUserType.Admin,
                                                             ref challenge,
                                                             ref lenChallenge
                                                             );
                }
                else
                {
                    dwChangePinStatus = dwLockCardStatus;
                }
            }
调用后 challenge 得到的值不正确请问 是不是我在DllImport后用C#写的参数不对？

Answer 1

ref byte[] pbChallenge,//这里有问题 , c++ ** 是指向指针的指针它意思是要在dll开辟内存，不能用ref ,  try out

Answer 2

谢谢 hdt(倦怠) 兄
[DllImport("cardmgr.DLL", SetLastError = true)]
        public static extern uint CMGetChallenge
            (
            IntPtr hContext,
            [MarshalAs(UnmanagedType.LPWStr)] string pwszUserName,
            [Out] byte[] pbChallenge,
            ref int cbChallenge);
我改成上面的签名后
在调用时pbChallenge的值有改变了，但是pbChallenge中只有前3个有值其他的都是0，正常情况下应该全部都有值。
如果 把[Out] byte[] pbChallenge 改成out byte[] pbChallenge，则pbChallenge中没有任何值。

Answer 3

直接把ref 或者 out去掉应该可以...byte[]在C#里面访问的时候应该就是用首地址,如果再指定ref的话......明白?

Answer 4

给你个例子
c++ dll 
int TestRefArrayOfInts(int** ppArray, int* pSize);
C# 申明
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
 public static extern int TestRefArrayOfInts( ref IntPtr array, 
      ref int size );
调用
 int[] array2 = new int[ 10 ];
      int size = array2.Length;
      Console.WriteLine( "\n\nInteger array passed ByRef before call:" );
      for( int i = 0; i < array2.Length; i++ )
      {
         array2[ i ] = i;
         Console.Write( " " + array2[ i ] );
      }
      IntPtr buffer = Marshal.AllocCoTaskMem( Marshal.SizeOf( size ) 
         * array2.Length );
      Marshal.Copy( array2, 0, buffer, array2.Length );
      
      int sum2 = TestRefArrayOfInts( ref buffer, ref size );
      Console.WriteLine( "\nSum of elements:" + sum2 );
      if( size > 0 )
      {
         int[] arrayRes = new int[ size ];
         Marshal.Copy( buffer, arrayRes, 0, size );
         Marshal.FreeCoTaskMem( buffer );
         Console.WriteLine( "\nInteger array passed ByRef after call:" );
         foreach( int i in arrayRes )
         {
            Console.Write( " " + i );
         }
      }
      else
         Console.WriteLine( "\nArray after call is empty" );

Answer 5

to: tisocoff()
你的方法 我已经试过了 行不通。
to:hdt(倦怠) 
我试试修改看。

Answer 6

to:hdt(倦怠) 
多谢老兄了 我按照你给的例子改完后可以正常工作了。以下是代码：
 [DllImport("cardmgr.DLL", SetLastError = true)]
        public static extern uint CMGetChallenge
            (
             IntPtr hContext,
            [MarshalAs(UnmanagedType.LPWStr)] string pwszUserName,
            ref IntPtr pbChallenge,
            ref int cbChallenge);
调用代码：
 IntPtr hContext = new IntPtr();
            int lenChallenge = 8;
           
            IntPtr buffer = Marshal.AllocCoTaskMem( Marshal.SizeOf( lenChallenge ));            /* Acquire the card context -----------------------------------------*/
            dwAcquireCardStatus = CardMgrWrapper.CCAcquireSingleCard(ref hContext);
            if (dwAcquireCardStatus == 0)
            {
                /* Lock the card to begin a transaction --------------------------*/
                dwLockCardStatus = CardMgrWrapper.CCLockCard(hContext, 0);
                if (dwLockCardStatus == 0)
                {
                    dwChangePinStatus = CardMgrWrapper.CMGetChallenge(hContext,
                                                             SCUserType.Admin,
                                                             ref buffer,
                                                             ref lenChallenge
                                                             );
                }
                else
                    // pass on the LockCard failed error code to be returned.
                    dwChangePinStatus = dwLockCardStatus;
            }
            else
                // pass on the AcquiredSingleCard failed error code to be returned.
                dwChangePinStatus = dwAcquireCardStatus;            /* Unlock the card --------------------------------------------------*/
            if (dwLockCardStatus == 0)
                CardMgrWrapper.CCUnlockCard(hContext, 0);            /* Release the card -------------------------------------------------*/
            if (dwAcquireCardStatus == 0)
                CardMgrWrapper.CCReleaseCard(hContext);
            if (dwChangePinStatus != 0)
            {
                throw new Exception(string.Format("Error:{0} HEX:{1}", dwChangePinStatus, Convert.ToString(dwChangePinStatus, 16)));
            }
            byte[] arrayRes = new byte[lenChallenge];
            Marshal.Copy(buffer, arrayRes, 0, lenChallenge);
            Marshal.FreeCoTaskMem(buffer);
            string challenge = "";
            foreach (byte b in arrayRes)
            {
                challenge += Convert.ToString(b, 16);
            }