Develop Reference

Converting a C struct to C#?

I have an API written in C++ and am attempting to use this with interop in C# Windows forms.
I am having difficulty defining the equivalent C# struct.
Here is the C++ struct:
typedef struct
{
char SerNo[LENGTH];
HANDLE dev;
} myDevice;
Edit:
Thanks to the comments the first item is solved.
Here is the current C# status:
public unsafe struct sdrplay_api_DeviceT
{
[MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 64)]
string SerNo;
public IntPtr dev;
}
However nothing I try get's the HANDLE. So I guess at this time, I will expand on the code further:
In the original C++ code, there is a function as follows:
GetDevices(myDevice *devs);
and in the C# code I have done this:
public unsafe static extern GetDevices([In, Out] myDevice[] devs);
Now the code I use is as follows:
myDevice[] devs = new myDevice[6];
var error = GetDevices(devs);
If I look at devs in Visual Studio I see the SerNo (devs[0].SerNo) correctly but the "handle is always 0;
I tried IntPtr, byte, but I am at a loss.
Thanks, Tom

Adding a CUDA dll as a reference to a C# project showing an error

I have made a Simple CUDA dll the code which I am displaying below. The function adds some value to an array.
#include<stdio.h>
#include<stdlib.h>
#include<cuda.h>
//Cuda Kernel
__global__ void add_gpu(float *a)
{
int idx=blockIdx.x*blockDim.x+threadIdx.x;
a[idx]=a[idx]*2;
}
int cudasafe( cudaError_t error)
{
if(error!=cudaSuccess)
return 1;
else
return 0;
}
extern "C" int __declspec(dllexport) __stdcall add_gpu_cu(float *a, int size,int nblock, int nthread)
{
float* dev_a;
int flag;
flag=cudasafe(cudaMalloc((void**)&dev_a,size*sizeof(float)));
if(flag==1)
return flag;
flag=cudasafe(cudaMemcpy(dev_a,a,size*sizeof(float),cudaMemcpyHostToDevice));
if(flag==1)
return flag;
add_gpu<<<10,10>>>(dev_a);
flag=cudasafe(cudaMemcpy(a,dev_a,size*sizeof(float),cudaMemcpyDeviceToHost));
if(flag==1)
return flag;
}
The problem is I cant add the dll created as a reference to my c# project. It throws up an exception saying a reference to the file could not be added. Make sure the file is accessible, and that its a valid assembly or COM component.
Am i doing something wrong in creating the dll?
Please help
Regards

No, the DLL is a C++ DLL, and not a .NET DLL, so you can't add a reference to it. You need to use interop to use it in C#.
To do so, you need to include a .DEF file in your DLL (or the __declspec) to make the function exportable, then declare the definition in C# along the lines of:
[DllImport("your_dll_name")] public static extern int add_gpu_cu(IntPtr a, int size, int nblock, int ntrheac);

Reference must be a managed DLL, i.e. it must be written with MSIL. You use unmanaged library currently. Here's a cool tutorial on making unmanaged calls from .NET.

Access Violation Exception

I am having some strange problem. I have written a small module in VC++ using OpenCV.
It works fine. The code aggregates feed from the CCTV camera connected to the USB port.
however, I had to write the rest of my application in C#, so I made a DLL of the VC++ code and called the VC++ method from C#.
Now, I have ended up getting an error
Attempted to read or write protected memory.
This is often an indication that other memory is corrupt.
Can anyone please suggest me any solution to this. Is there any Access Violation while accessing it in a managed code?

If TrackBlob returns a string, you should be able to define your dllimport as such:
[DllImport("Tracking.dll", EntryPoint = "TrackIt")]
public extern static string TrackBlob();
and skip trying to marshal it.
By returning it as an IntPtr, you're trying to get a pointer into memory owned by the unmanaged DLL... returning it as a string will return a copy of the string for you to work with.
Let me know if that works!
James
* Edit *
Try one of these:
[DllImport("Tracking.dll", EntryPoint = "TrackIt")]
public extern static [MarshalAs(UnmanagedType.BStr)] string TrackBlob();
or
[DllImport("Tracking.dll", EntryPoint = "TrackIt")]
public extern static [MarshalAs(UnmanagedType.AnsiBStr)] string TrackBlob();
Check out this MSDN link on string marshalling:
http://msdn.microsoft.com/en-us/library/s9ts558h.aspx

Accessing "Mapi32.dll" with C#

I am using VS 2008 C#
Windows Application.
I have this DLL Import I am trying to use.
[DllImport("Mapi32.dll", PreserveSig = true)]
private static extern void
WrapCompressedRTFStream(
[MarshalAs(UnmanagedType.Interface)]
UCOMIStream lpCompressedRTFStream,
uint ulflags,
[MarshalAs(UnmanagedType.Interface)]
out UCOMIStream lpUncompressedRTFStream
);
public const uint MAPI_MODIFY = 0x00000001;
public const uint STORE_UNCOMPRESSED_RTF = 0x00008000;
I have a compressed string that is in CompressedRFTFormat.
How do I pass the string into the WrapCompressedRTFStream? I do not understand what the method is expecting.
I am trying to use it on a button.
RichText1.text = WrapCompressedRTFStream(_CompressedRichText.ToString(),something,somethingelse);
The first error I get is "cannot convert from 'string' to 'System.Runtime.InteropServices.UCOMIStream"
I hope someone who understands this posts an answer that helps!
ok, so I end up in the same situation when I use the IStream.
[DllImport("Msmapi32.dll", PreserveSig = true)]
private static extern void WrapCompressedRTFStream(
[MarshalAs(UnmanagedType.Interface)]
IStream lpCompressedRTFStream,
uint ulflags,
[MarshalAs(UnmanagedType.Interface)]
out IStream lpUncompressedRTFStream
);
The real issue here is I do not understand what / how to deal with the input and output of this method.

I suppose it's not a good idea to use legacy native-code libraries & I would investigate some more time to find analogous code in .net
Try out com interop or p-invoke .net technologies to use legacy code.

If you can't find a native .NET method for doing this, a good approach would be to contain your approach in a Managed C++ wrapper.
What this will let you do is create C++ code to perform your work, while exposing a managed class to call the method. This may be more complicated since it will require you to learn Managed C++, but allows you to do any C++ work necessary, returning a .NET string containing your "answer".

UCOMIStream is deprecated, use ComTypes.Istream instead. Then look at System.Runtime.InteropServices.ComTypes.IStream to System.IO.Stream

"Unable to find an entry point named [function] in dll" (c++ to c# type conversion)

I have a dll which comes from a third party, which was written in C++.
Here is some information that comes from the dll documentation:
//start documentation
RECO_DATA{
wchar_t Surname[200];
wchar_t Firstname[200];
}
Description:
Data structure for receiving the function result. All function result will be
stored as Unicode (UTF-8).
Method:
bool recoCHN_P_Name(char *imgPath,RECO_DATA *o_data);
Input:
char * imgPath
the full path of the image location for this
function to recognize
RECO_DATA * o_data
data object for receiving the function
result.
Function return:
True if Success, otherwise false will return.
//end documentation
I am trying to call the recoCHN_P_Name from my C# application. To this end, I came up with this code:
The code to import the dll:
public class cnOCRsdk
{
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct RECO_DATA{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=200)]
public string FirstName;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 200)]
public string Surname;
}
[DllImport(#"cnOCRsdk.dll", EntryPoint="recoCHN_P_Name")]
public static extern bool recoCHN_P_Name(byte[] imgPath, RECO_DATA o_data);
}
The code to call the function:
cnOCRsdk.RECO_DATA recoData = new cnOCRsdk.RECO_DATA();
string path = #"C:\WINDOWS\twain_32\twainrgb.bmp";
System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
byte[] bytes = encoding.GetBytes(path);
bool res = cnOCRsdk.recoCHN_P_Name(bytes, recoData);
And the error I'm getting is
""Unable to find an entry point named 'recoCHN_P_Name' in DLL 'cnOCRsdk.dll'."
I'm suspecting that I'm having an error in converting a type from C++ to C#. But where exactly ... ?

First make sure the function is actually exported:
In the Visual Studio Command Prompt, use dumpbin /exports whatever.dll

C# doesn't support C++ name mangling and you either need to declare the C++ functions with
extern "C" {...}
(may not an option if they're from a third party), or call the mangled name directly if you can get it to work. It may be easier to get the third party to provide a non-mangled interface to the functionality.

Solved - at least to the point where the program does not break and actually returns me a bool value.
The key, I guess, was to specify the entry point as the 'mangled' name
[DllImport(#"cnOCRsdk.dll", EntryPoint="?recoCHN_P_Name#CcnOCRsdk##QAE_NPADPAURECO_DATA###Z")]
public static extern bool recoCHN_P_Name(ref string imgPath, ref RECO_DATA o_data);
After that I got some other errors but the 'unable to find entry point' went away.

I solved the same problem in these steps:
step 1) If you program your custom DLL in C++ using Visual studio,then at the property page of your project set the Common Language Runtime Support (/clr)parameter to Common Language Runtime Support (/clr).
step 2) To function deceleration in .h file use __declspec(dllexport) keyword like below:
__declspec(dllexport) double Sum(int a,int b);
step 3) Build and export DLL file, then use the Dependency Walker software to get your function EntryPoint.
step4) Import DLL file In the C# project and set EntryPoint and CallingConvention variable like below:
[DllImport("custom.dll", EntryPoint = "?Sum##YAXHHHHHHNNN#Z", CallingConvention = CallingConvention.Cdecl)]
public static extern double Sum(int a,int b);

I'd write a wrapper using C++/CLI. This wrapper will be able to include the .h files and link to the .lib files you got from the third party vendor. Then it is both easy and safe to write a managed interface for your C# program.

Correct EntryPoint string could be found in ".lib" file that comes along with main unmanaged dll.

We had this problem when we want to access to DB and solved it by changing EF core to EF 6.4.4
It may be you have a problem like this and need to change or downgrade your version of EF (If you used EF)

We had this problem .we change EntityFramework.core to EntityFrameWork 6.4.4 and after that the program worked fine. you most change you're Framework Version.

you may get this error due to string marshalling mismatch between DLL and your application . for example, one is using ANSI and the other is unicode.
you can try something like this:
[DllImport("yourDLL.dll", CharSet = CharSet.Unicode )]
public static extern String YourFunction(String name);
checkout HERE for a list of other possible reasons.

You could try using the unmangled name while specifying a CallingConvention in the DllImport