Correct convert/marshall C Function and DLL Structure type to C#

Question

Hi Can someone please help me convert my C structure/function into C#? I really need this badly... I believe I can call the DLL properly if I have able to correctly convert the function and marshal properly my structure. Here is my struct and the function that uses it: [CODE] typedef struct UIclient_info { char name[50]; int age; SECONDUSER *stParent; } FIRSTUSER; typedef struct ui_product_form { char m_sCoupon; double amountTotal; char m_sErrorCode[50]; SUBPRODUCT *pstSubProduct; } PRODUCT; typedef struct tagReport { REPORTSUMMARY *pstRepsum; char errorMsg[100]; }FINAL_REPORT; int Save(FIRSTUSER *myUser PRODUCT *uiStructure) FINAL_REPORT GenerateReport(FIRSTUSER *myUser PRODUCT *uiStructure) [/CODE] PLEASE HELP. Thanks in advance. -dantz

Vulpes · Answer

I take it that there's no exception. Are you getting any output at all even if it's wrong?

dantz · Answer

What data does the DLL fill in with the Save method? I'd have thought that if there were any SECONDUSER or SUBPRODUCT info you'd fill that in yourself. You would then need to use AllocHGlobal to allocate memory for that. However if there's an error then the error code string will be filled in by the DLL using the pointer to the structure (i.e. the class reference) you're passing to it. Just noticed though that the errorCode field should be defined as string not char. Sorry missed that in my first response: [StructLayout(LayoutKind.Sequential CharSet=CharSet.Ansi)] public class PRODUCT { public char coupon; public double amountTotal; [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] public string errorCode; public IntPtr pstSubProduct; } The DLL will fill in the correct amountTotal base on the coupon that I send. And also the errorCOde why it change the amountTotal. Is it correct to convert my save method to accept IntPtr parameter like this: IntPtr myUserStruct = Marshal.AllocHGlobal(Marshal.SizeOf(firstUser)); IntPtr myProductStruct = Marshal.AllocHGlobal(Marshal.SizeOf(myProduct)); Save(myUserStruct myProductStruct); I will initialize my values then convert to IntPtr is that the correct way? I have done the above but I still can't get my output to the DLL. What I am missing? Appreciate your help on this.

Vulpes · Answer

What data does the DLL fill in with the Save method? I'd have thought that if there were any SECONDUSER or SUBPRODUCT info you'd fill that in yourself. You would then need to use AllocHGlobal to allocate memory for that. However if there's an error then the error code string will be filled in by the DLL using the pointer to the structure (i.e. the class reference) you're passing to it. Just noticed though that the errorCode field should be defined as string not char. Sorry missed that in my first response: [StructLayout(LayoutKind.Sequential CharSet=CharSet.Ansi)] public class PRODUCT { public char coupon; public double amountTotal; [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] public string errorCode; public IntPtr pstSubProduct; }

dantz · Answer

Hi Vulpes My DLL still not able to get it. My struct will be read and the DLL will fill-in data inside. Is there no need for AllocHGlobal ? Thanks for the reply

Vulpes · Answer

Try: FIRSTUSER firstUser = new FIRSTUSER(); firstUser.age = 20; firstUser.name = dantz; firstUser.stParent = IntPtr.Zero; MYPRODUCT myProduct = new MYPRODUCT(); myProduct.m_sCoupon = 'A' myProduct.amountTotal = 18000.50; myProduct.pstSubProduct = IntPtr.Zero; NativeTest.Save(myUserStruct myProductStruct); You shouldn't need to use AllocHGlobal if you're setting the IntPtr fields to zero.

dantz · Answer

I am currently exploring this now: FIRSTUSER firstUser = new FIRSTUSER(); firstUser.age = 20; firstUser.name = dantz; firstUser.stParent = IntPtr.Zero; char[] prodCOupon = new char[1] { 'A' }; MYPRODUCT myProduct = new MYPRODUCT(); myProduct.m_sCoupon = Encoding.ASCII.GetBytes(prodCOupon)[0]; myProduct.amountTotal = 18000.50; IntPtr myUserStruct = Marshal.AllocHGlobal(Marshal.SizeOf(firstUser)); IntPtr myProductStruct = Marshal.AllocHGlobal(Marshal.SizeOf(myProduct)); NativeTest.Save(myUserStruct myProductStruct); Marshal.FreeHGlobal(myUserStruct); Marshal.FreeHGlobal(myUserStruct); However my DLL is not able to read the data that I have initialized. Am I missing something? Please help me here. I think I am almost near to my solution. Thanks in advance.

dantz · Answer

Thanks Vulpes! With regards to this: 4. If the unmanaged code (or your code) is going to fill a memory block with SECONDUSER SUBPRODUCT and REPORTSUMMARY details then you will need to use Marshal.AllocHGlobal to allocate memory on the unmanaged heap and return an IntPtr to it for embedding in the class. Fill a memory block means there was a malloc instantiated inside the DLL? I guess I really need these because when I call the DLL functions my data was NOT received by the DLL. When I search on Marshal.AllocHGlobal it returns an IntPtr. I am not too sure how can I transfer this to my function call? Can please guide me on this? thanks.

Vulpes · Answer

A few points on that: 1. If you're using classes rather than structs then it's not necessary to pass them by reference to the two methods - they're references already. The final semi-colons are not needed in C# though you can use them if you like. 2. I'd specify CharSet = CharSet.Ansi in the StructLayout attributes if the unmanaged code is using ANSI strings and chars. 3. The fields in your classes need to be declared as public so you can access them - they're not public by default as they are in a C struct. 4. If the unmanaged code (or your code) is going to fill a memory block with SECONDUSER SUBPRODUCT and REPORTSUMMARY details then you will need to use Marshal.AllocHGlobal to allocate memory on the unmanaged heap and return an IntPtr to it for embedding in the class. 5. In the case of FINAL_REPORT I think you'll have to declare it as a struct rather than a class as the GenerateReport function is returning it by value. Return values which are structs can be a troublesome area when using P/Invoke and I think you'll just have to try it and see. [StructLayout(LayoutKind.Sequential CharSet=CharSet.Ansi)] public class FIRSTUSER { [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] public string name; public int age; public IntPtr stParent; } [StructLayout(LayoutKind.Sequential CharSet=CharSet.Ansi)] public class PRODUCT { public char coupon; public double amountTotal; [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] char errorCode; public IntPtr pstSubProduct; } [StructLayout(LayoutKind.Sequential CharSet=CharSet.Ansi)] public struct FINAL_REPORT { public IntPtr pstRepsum; [MarshalAs(UnmanagedType.ByValTStr SizeConst=100)] public string errorMsg; } [DllImport(SQSCode.dll)] public static extern int Save(FIRSTUSER myUser PRODUCT uiStructure); [DllImport(SQSCode.dll)] [return:MarshalAs(UnmanagedType.Struct)] public static extern FINAL_REPORT GenerateReport(FIRSTUSER myUser PRODUCT uiStructure);

dantz · Answer

Regarding my original question I was actually thinking of doing DLLImport on the DLL then create a structure/class that would represent (I don't know it is called) its structure C# This is what I created Please correct me if I am wrong: [StructLayout(LayoutKind.Sequential)] public class FIRSTUSER { [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] string name; int age; IntPtr stParent; }; [StructLayout(LayoutKind.Sequential)] public class PRODUCT { char coupon; double amountTotal; [MarshalAs(UnmanagedType.ByValTStr SizeConst=50)] char errorCode; IntPtr pstSubProduct; }; [StructLayout(LayoutKind.Sequential)] public class FINAL_REPORT { IntPtr pstRepsum; [MarshalAs(UnmanagedType.ByValTStr SizeConst=100)] string errorMsg; }; [DllImport(SQSCode.dll)] public static extern int Save(ref FIRSTUSER myUser ref PRODUCT uiStructure); [DllImport(SQSCode.dll)] public static extern FINAL_REPORT GenerateReport(ref FIRSTUSER myUser ref PRODUCT uiStructure); Is this correct? Do I need some AllocHGlobal(IntPtr) with this?

dantz · Answer

Hi Javeed Thanks for the immediate reply. I cannot easily recompile with /CLR I am not sure why. Below are the switch I am using. /Zi /clr /nologo /W3 /WX- /Od /Oy- /D _MBCS /EHa /GS /fp:precise /Zc:wchar_t /Zc:forScope /FpDebug\SQSLibraryTest.pch /FaDebug\ /FoDebug\ /FdDebug\vc100.pdb /analyze- /errorReport:queue Just a follow up question If the creators of the library can compile it in Visual Studio 2010 C++ Project. Does it mean I can use it in C#? Is it possible to call those C functions in my C# codes?

Javeed M Shaikh · Answer

Hi Dantz What I would suggest is to compile your C code in a Visual Studio.NET C++ project with the /CLR switch and it will be compiled into a .NET managed assembly. You can than use that in your C# code. I am not sure of any direct converter from C to C#. Please do not forget to mark Accepted Answer.