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.
Related
I have a DLL that was developed in Visual C++, and I've started importing it's functionality to a c# project using DllImport. I've already implemented a few methods and they work well.
For that specific method I'm getting the following error:
Additional information: A call to PInvoke function 'SdkTest!SdkTest.Program::CLIENT_RealPlay' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.
The c++ method I'm trying to implement has this signature:
CLIENT_NET_API LLONG CALL_METHOD CLIENT_RealPlay(LLONG lLoginID, int nChannelID, HWND hWnd);
With the following definitions:
#define CLIENT_NET_API __declspec(dllimport)
#define CALL_METHOD __stdcall
#define LLONG LONG
My c# impelmentation is the following:
[DllImport("dhnetsdk.dll")]
public static extern long CLIENT_RealPlay(long lLoginID, int nChannelID, IntPtr hWnd);
(I've read that HWND equivalent in c# is IntPtr, but I've also tried to put int, long, object...)
I also tried doing DllImport in the following way (As suggested in some posts and worked for some other methods I'm using):
[DllImport("dhnetsdk.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
No matter what I try I'm getting the same error. What am I miss understanding? If an internal exception in the c++ code is thrown, what kind of exception will I get in my code?
#define LLONG LONG
Now, LONG maps to long, which is a signed 32 bit type on Windows. Therefore, using long in your C# code is wrong because C# long is a 64 bit type. You need to use int instead. Like this:
[DllImport("dhnetsdk.dll")]
public static extern int CLIENT_RealPlay(int lLoginID, int nChannelID, IntPtr hWnd);
The c++ function is declared with calling convention stdcall, but you are calling it with cdecl.
In my experience, call stack corruptions are mostly caused by using the wrong calling convention.
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?
I'm trying to write a bare-bones ultra-simple light-weight wrapper for the LibVLC DLL Library. I don't need access to much, just the ability to play pause and stop media files. I'm looking at the documentation and this other link I found that explains an older version of LibVLC, but it's outdated for the most recent version. I also tried LibVLC.Net but it too is outdated and I can't find what I'm looking for in the source code to match it to the functions I'm trying to export.
I have the following signature I'm trying to export:
libvlc_new (int argc, const char *const *argv)
The description:
argc the number of arguments (should be 0)
argv list of arguments (should be NULL)
And this is the method I'm trying.
[DllImport("libvlc", EntryPoint = "libvlc_new")]
public static extern IntPtr New(Int32 argc, String[] argv);
The description suggests it should be an array, and I think the problem is the second argument. I've tried:
[MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr)] String[] argv
as according to here, and there are a couple of other options such as a String and StringBuilder as suggested here but it still happens that every time I call the function I get an Imbalanced PInvoke stack.
I need to know what the proper calling convention of this, and very likely several other, functions are. A "PInvoke For Dummies" online reference would be super good.
Not much point in declaring the argument type if only NULL is permitted. Just declare it IntPtr and pass IntPtr.Zero.
The debugger is pointing out that you forgot to declare the CallingConvention. It is not the default for .NET, this is a __cdecl function. So the proper declaration would be:
[DllImport("libvlc", EntryPoint = "libvlc_new",
CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr New(int argc, IntPtr argv);
Called as:
New(0, IntPtr.Zero);
Do try to pick a better name...
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)
I am a C/C++ programmer, but I was asked to update a program that was written in C# to communicate with a device. My knowledge of C# is very basic.
The previous version was totally written in C#, but now the API that in fact access the device was changed to C. I found out that I can import the C function APIs by using:
[DllImport("myapi.dll")]
public static extern int myfunct(
[MarshalAs(UnmanagedType.LPTStr)] string lpDeviceName,
IntPtr hpDevice);
In C this function prototype is:
int myFunct( LPTStr lpDeviceName, HANDLE* hpDevice );
Where HANDLE is defined as :
typedef void *HANDLE;
However this function does not work as expected. In fact, in the C# code call what kind of type I should declare and pass to the C# method?
Thanks for the help and sorry for any stupid question.
Actually, this is the wrong way of marshalling HANDLE *. It'll work, but not be reliable in the face of exceptions.
The function you posted looks like an object creation function (it's treating hpDevice as an output parameter, and returning an int status result).
The correct way to marshal it depends on exactly what type of object it's creating and how it is closed. Assuming that the HANDLE is closed by calling CloseHandle (which is true for most but not all HANDLE objects), then you can probably use one of the types that inherits from SafeHandleZeroOrMinusOneIsInvalid. For example, if the object is a registry key, then use SafeRegistryHandle; if it's a file, then use SafeFileHandle.
If it's some type for which there isn't an existing safe handle type (but does use CloseHandle to close it), then you'll have to define your own safe handle type derived from SafeHandleZeroOrMinusOneIsInvalid. If it's some type that doesn't use CloseHandle to close it, then you'll have to define your own safe handle type derived from SafeHandle.
Once you have determined the correct SafeHandle-derived type, then you can use it in the function call (using SafeFileHandle as an example):
[DllImport("myapi.dll")]
public static extern int myFunct(
[MarshalAs(UnmanagedType.LPTStr)] string lpDeviceName,
out SafeFileHandle hpDevice);
you are passing IntPtr instead of ref IntPtr, the definition should look like this:
[DllImport("myapi.dll")]
public static extern int myfunct(
[MarshalAs(UnmanagedType.LPTStr)] string lpDeviceName,
ref IntPtr hpDevice);