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typedef void* alternative in c#

I am using DLL runtime which is made with C language into C#.
I came across below statement.
typedef void *JCCP_PROPERTY_HANDLE;
In function it is being used as:
JCCP_RESULT __JCCP_FUNCTION__ jccpGetProperty(
JCCP_HANDLE hjccp,
const char *name,
JCCP_PROPERTY_HANDLE *phproperty);
Now I want to call jccpGetProperty() method in my C# code.
Can anybody tell how can I pass third parameter(JCCP_PROPERTY_HANDLE *phproperty) to function from C#.
I tried with below code but not working.
Extern Method:
[DllImport(DLL_NAME, EntryPoint = "_jccpGetProperty", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr jccpGetProperty(IntPtr hjccp, string name, ref IntPtr JCCP_PROPERTY_HANDLE);
Usage
IntPtr handle = IntPtr.Zero;
string tag = "server.version";
var result = jccpGetProperty(hjccp, tag, ref handle);
Can anybody help me in this?

IntPtr is the correct type mapping for void*. The native type void* is generally used for an opaque pointer, and that is mapped to IntPtr in C#.
Those parts of the p/invoke declaration that we can verify are correct. The unverifible parts are:
The calling convention. You believe that it is cdecl, but we can't check.
The return type. You believe it to be pointer sized. Again we cannot check. My guess is that a 32 bit integer, int or uint is more likely. That would make a difference in a 64 bit process.
The values passed to the function. It's perfectly possible that the function is declared correctly, but you are passing invalid values.
Because you only showed partial code and details, it's hard to say much more. You will have to verify all the parts of the program that we cannot.
I suggest that you start with working C or C++ code and translate that, looking for the first point of deviation in behaviour between that code and your C# translation.

Call to external DLL from C# with integer pointer

I'm trying to call an external .dll function from c#. The doc for the dll defines the function:
int funcName(int *retVal)
I've tried various configurations and always the unbalanced stack error from p/invoke; My c# code currently looks like this:
[DLLImport("dllName");
unsafe static extern int funcName(ref IntPtr retVal);
unsafe IntPtr retNum;
int status = funcName(ref retNum);
Any ideas are appreciated!

Your p/invoke declaration has the wrong parameter type.
ref Int32 is the correct match for int*.
IntPtr can also work.
ref IntPtr would be int**. Definitely not what you want.
Use
[DLLImport("dllName")]
static extern int funcName(ref Int32 retVal);
Also make sure that the calling convention matches. You should never use a dllexport in C or C++ without also using an explicit calling convention, and then the C# DllImport needs to have the matching convention.
Generally the prototype in C++ should be
extern "C" int __stdcall funcName(int* arg);
Is there a header file provided for C and C++ clients that you could check to verify the signature?

How to marshal two dimensional TCHAR array?

I have a DLL function in that converts a file to another format.
The function produces multiple files as output.
Therefore, it fills the 2nd parameter with the paths of the output files.
The C++ function is defined as the following:
int Convert(LPTSTR lpSource, TCHAR outputFileName[][MAX_PATH]);
How do I mashal the 2nd parameter so that my C# application can receive the output file paths correctly?
[DllImport("Convert.dll")]
private static extern int Convert(
[MarshalAs(UnmanagedType.LPTStr)] string lpszSource,
????
);
Thanks in advance.

I would make things simpler using C++/CLI (which is very good at building bridging layers between native C/C++ code and managed code).
Basically, you could write a thin C++/CLI layer that exposes a method that calls the native function in its body, and then copies the returned native strings into a gcnew-ly created array<String^>, and returns it to the C# managed caller.

I finally figured it out.
I changed my C++ function to the following:
int Convert(LPTSTR lpSource, LPTSTR *plpOutputFileName, int size);
And the C# declaration as:
[DllImport("Convert.dll")]
private static extern int Convert(
[MarshalAs(UnmanagedType.LPTStr)] string lpszSource,
[In, Out] String[] outputFileName,
int size
);
Thank you all for helping.

PInvoke in 64bit .net app through c++ 64 bit dll

I'm having an issue calling a function in a c++ dll inside of a c# app. I'm calling the function inside of c# like so:
[DllImport("cryptopp.dll")]
public static extern IntPtr RSAEncryptString(string filename, string seed, string message);
It is being exported in the c++ dll as shown below.
extern "C" __declspec(dllexport) const char* __cdecl RSAEncryptString(const char *pubFilename, const char *seed, const char *message);
What I get when I try to call this, however, is an "An External component has thrown an exception." exception, which is not very descriptive at all, and extremely unhelpful.
When I pull up the dll in an export viewer, it shows all the other exported functions with fully quantified declarations (I.E. public: void __cdecl CryptoPP::X509PublicKey::`vbase destructor'(void) __ptr64 ) , except for the function I am calling, which just displays the function name RSAEncryptString.
This is the only possible issue I can see, besides maybe mis-calling the function with an invalid declaration on the c# side. Am I using System.Runtime.InteropServices.Marshal wrong?
Please help <3 and thanks in advance.

I think you need to change the first line to:
[DllImport("cryptopp.dll",
CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
If you want to get very descriptive, you can also add these:
public static extern IntPtr RSAEncryptString(
[In, MarshalAs(UnmanagedType.LPStr)] string filename,
[In, MarshalAs(UnmanagedType.LPStr)] string seed,
[In, MarshalAs(UnmanagedType.LPStr)] string message);
IIRC think the CharSet should take care of the encoding thing for you, but if it doesn't, use the MarshalAs also, as shown above.
Edit:
Oh I think I got why you still get an error! Your code still had the above problems, but it's still erring because you can't return a string object since it's not a managed object; you need to return a pointer (like IntPtr) and then use Marshal.PtrToStringAnsi!
(I didn't really look at your return type when answering this at first.)

It appears you're trying to store the return value of type const char * (an LPCSTR) into an IntPtr type (usually used for HANDLEs, not LPSTRs.) Try this:
[DllImport("cryptopp.dll", CharSet = CharSet.Auto)]
public static extern String RSAEncryptString(String filename, String seed, String message);
Also keep in mind that if any argument is getting written to, you'll need to add out before its type, i.e. ..., out String message)

C# dll import function correctly

I am trying to import a function from a c dll into C#. The c function looks like this
unsigned short write_buffer( unsigned short device_number, unsigned short word_count, unsigned long buffer_link, unsigned short* buffer)
my attempt at a C# import looks like this
[DllImport("sslib32.dll", CharSet = CharSet.Ansi, SetLastError = true)]
private static extern ushort write_buffer(ushort deviceNumber, ushort wordCount, UInt32 bufferLink, IntPtr buffer)
In C# i have a Dictionary of messages that i would like to pass to this function. The Dictionary looks like this:
Dictionary<string, List<ushort>> msgs
I am a bit confused how to make a make a proper call to pass msgs as the buffer. deviceNumber is 2, wordCount is 32, and buffLink is 0. So i know the call should look something like this
write_buffer(2,32,0, msgs[key]);
Obviously i am getting an invalid argument for the IntPtr. What is the proper way to make this call?

It is quite unclear what buffer should contain and in which direction its data flows. Your dictionary suggests it should be an array. Just declare it that way:
private static extern ushort write_buffer(.., ushort[] buffer);
And use msgs[key].ToArray() in the call.
Using constants in the write_buffer() call does not make that a likely scenario though, there ought to be msgs[key].Count in there somewhere.

You can generate P/Invoke signatures using the P/Invoke Interop Assistant tool that is referenced here.
In the January 2008 issue of the MSDN
Magazine, Yi Zhang and Xiaoying Guo
have published a CLR Inside Out column
on marshaling between managed and
unmanaged code. In that column, they
introduce the P/Invoke Interop
Assistant, an automatic GUI and
command-line utility for converting
between managed and unmanaged
signatures (in both directions). This
conversion, of course, is not limited
just to Windows signatures; give the
tool a snippet of your own C header
files and it will dutifully convert
them to pretty-printed C#
[DllImport]'s.

If you don't mind marking the code unsafe, you can simply do:
fixed(ushort* pData = msgs[key])
{
write_buffer(2,32,0, pData);
}
And declare your DllImport to take ushort* as the last argument.
The alternative is to use Marshal.StructureToPtr to get the array marshalled into fixed memory. This requires you to allocate memory first using AllocHGlobal, and freeing using FreeHGlobal.