c#调用delphi开发的dll的指针参数

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在c#中调用DELPH编写的DLL的函数时出现未将对象引用到实例的错误： delphi编写的dll中函数声明：function DeliverfromEsm(var Smtype, Content,Caller:pchar):integer;

Content：短信内容或报告（若Smtype为即时消息或离线消息，则Content表示短信内容；否则，Content表示返回的状态报告情况）； Content表示返回的状态报告Report结构： DWORD TaskID; //客户端序列号 TaskID DWORD MsgID; //客户端序列号 MsgID char UserNumber[22]; //接收手机号 unsigned char state; //状态 unsigned char ErrCode; //错误代码我在c#中声明： [DllImport("EsmApi.dll",CharSet = CharSet.Ansi,CallingConvention = CallingConvention.StdCall)] static extern int DeliverfromEsm(ref string smtype,ref string content,ref string caller); 调用： string smtype=""; string content=""; string caller=""; int reportval=DeliverfromEsm( ref smtype,ref content,ref caller); 出现未将对象引用到实例的错误

以下是解决办法：

声明：

[DllImport("EsmApi.dll",CharSet = CharSet.Ansi,CallingConvention = CallingConvention.StdCall)] static extern int DeliverfromEsm(StringBuilder Smtype, IntPtr Content,StringBuilder Caller);//接收短信和report

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi,Pack=1)] public struct Report { public int TaskID;//4byte public int MsgID; [MarshalAs(UnmanagedType.ByValTStr,SizeConst=22)]public string UserNumber; public byte state;//1byte public byte ErrCode; }

程序中处理：

StringBuilder smtype= new StringBuilder(256);//Init buffer

int size = Marshal.SizeOf(typeof(Report)); IntPtr content=Marshal.AllocHGlobal(size);//分配32bytes StringBuilder caller= new StringBuilder(256);//Init buffer int reportval=DeliverfromEsm( smtype,content, caller);

//字符串时

string smscontent=Marshal.PtrToStringAnsi(content);

//结构体时

Report content1=(Report)Marshal.PtrToStructure(content,typeof(Report));

Marshal.FreeHGlobal(content);//释放

参考了网上的一段代码：

[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)] public struct VideoCompressorInfo { [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)] public string szName; public Int32 dwHandle; } [DllImport("DSStream.dll")] public extern static int DSStream_EnumVideoCompressor(IntPtr pInfo, ref int piVidCompNum); int num = 0; DSStream_EnumVideoCompressor(IntPtr.Zero, ref num); int size = Marshal.SizeOf(typeof(VideoCompressorInfo)); IntPtr structPtr = Marshal.AllocHGlobal(size * num); DSStream_EnumVideoCompressor(structPtr, ref num); VideoCompressorInfo[] infos = new VideoCompressorInfo[num]; for (int i = 0; i < num; ++i) { infos[i] = (VideoCompressorInfo)Marshal.PtrToStructure((IntPtr)((int)structPtr + i * size), typeof(VideoCompressorInfo)); } Marshal.FreeHGlobal(structPtr);