I am trying to call an existing C dll from a C# application, using System.Runtime.InteropServices, and am having difficulty matching the signatures between the PInvoke function and the Target function.
The target function is
__declspec(dllexport) DWORD GetSomeString(char* strOut);
And my PInvoke function is
[DllImport("Existing.dll")]
public static extern uint GetSomeString([MarshalAs(UnmanagedType.LPWStr)]
string strDisplay);
I make the function call
string tempStr = "My Output String";
uint retVal = GetSomeString(tempStr);
But I get the message
Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem...
...A call to PInvoke function 'GetSomeString' 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.
I have also tried implementing the PInvoke function as
[DllImport("Existing.dll")]
public static extern uint GetSomeString([MarshalAs(UnmanagedType.LPWStr)]
StringBuilder strDisplay);
But to no avail.
Does anyone out there have an idea what I could be doing wrong?
Please let me know if further info is required or my question is unclear.
Thanks in advance.
You need to specify the calling convention. By default, PInvoke uses StdCall, but your method is (likely) Cdecl.
[DllImport("Existing.dll", CallingConvention=CallingConvention.Cdecl)]
In addition to the incorrect calling convention mentioned by Reed Copsey, the matching type for char* is UnmanagedType.LPStr.
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 have below function on C++ (header)
string __declspec(dllexport) *GetReaders(int& readerCount);
I wrote below method on C# for invoking
[DllImport("ABC.dll", CharSet = CharSet.Auto )]
extern static string[] GetReaders(out IntPtr readercount);
But after run I can got readercount but the app got below error:
Cannot marshal 'return value': Invalid managed/unmanaged type combination.
What is wrong?
I did it by java and work perfectly. But I have problem with .Net.
It's impossible to call that method with p/invoke. That's because you cannot marshal C++ classes using p/invoke. And string is, presumably, std::string.
You'll need to either use a C++/CLI wrapper, or re-design the C++ interface to be p/invoke friendly.
I have a C++ dll which is used to card printing( ID cards ). My implementation done using C#.Net. I used following code to call c++ dll.
[DllImport(#"J230i.dll",CallingConvention = CallingConvention.Cdecl,SetLastError=true)]
public static extern int N_PrintJobStatus(ref int[] nPrtintjobStatus);
int[] pJob = {0,0,0,0,0,0,0,0} ;
ret = N_PrintJobStatus( ref pJob);
N_PrintJobStatus method signature given as bellow
N_PrintJobStatus(int *pJobStatus )
After calling the method it gives following error
A call to PInvoke function '********!*********.frmCardPrint::N_PrintJobStatus' 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.
How can I fix this issue
thank you .....
Your translation is incorrect. An int array, int* does not map to ref int[]. The latter would be marshalled as int**. You need instead to use int[].
[DllImport(#"J230i.dll", CallingConvention = CallingConvention.Cdecl,
SetLastError = true)]
public static extern int N_PrintJobStatus(int[] nPrtintjobStatus);
Allocate the array before calling the function. Presumably you have some way to determine how long it should be. As it stands this function looks like a buffer overrun waiting to happen. How can the function know how long the array is and so take steps to avoid writing beyond its end?
It's not clear that this is the only problem. We cannot be sure that the return type really is int. Or that the calling convention is cdecl. Or that the function really does call SetLastError.
i have the following method signature on my c++ dll:
extern char *bpStringCalc(char *bpDirectory, char *issString);
And i'm trying to call it from c# using this:
[DllImport(#"C:\MuniAxis\Bp\BpDLL.dll", CharSet = CharSet.Ansi)]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern string bpStringCalc([MarshalAs(UnmanagedType.LPStr)] string bpDirectory,
[MarshalAs(UnmanagedType.LPStr)] string issString);
But it keep getting this exception:
'ConsoleApplication1!ConsoleApplication1.Program::bpStringCalc'
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.
Any ideas?
Thanks
Try specifying a Cdecl calling convention on import or __stdcall on export. See this almost similar question.
Unbalancing the stack probably has more to do with calling convention than it does the actual arguments. C++, by default, uses the __cdecl calling convention. C# defaults to __stdcall because __stdcall is the convention used by Win32. You need to either set calling convention on your import statement in C#, or you need to specify __stdcall in your C++ binary.
EDIT: The above was edited to fix the fact that __cdecl and __stdcall had only one leading underscore each ;)
I´m trying to call a method that is in a C++ dll declarated as __declspec(dllexport) to use in C#, but I don´t know how to return a string value from C++ and how to declare the signature using DllImport in C#.
C++ code "VNVAPI.dll"
__declspec(dllexport) char * GetGpuName(int phyGPUid)
{
CNvidia * pInstance = CNvidia::GetInstance();
char szName[512]={0};
pInstance->GetGpuName(phyGPUid,szName,512);
return szName;
}
C# method signature:
[DllImport("VNVAPI.dll")]
public static extern char GetGpuName(int phyGPUid);
Error generated:
A call to PInvoke function
'Core!Core.Hardware.IO.NVAPI::GetGpuName'
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.
Thanks.
As has been pointed out by others you need to specify the C calling convention in your P/Invoke and also use string on the managed side to marshal the null terminated char*.
However you should rejig the C++ routine to take a char* as an input parameter, together with a buffer length parameter. You then write into this buffer in the native code. This avoids the current problem that the data, as you presently have the code, is returned from the stack which, of course, is unwound as the function returns.
The suggestion to use static will make this memory global and so avoid stack unwind problems, at the expense of thread safety. Yes it will likely work for this use case but its a bad habit to get into.
The error message might be confusing.
Without going into detail, try this:
static char szName[512]={0};
If you still get the error, the you need to specify the calling convention in the DllImport attribute.
Edit:
Also make the return type string for C# method declaration.
The error message suggests checking the calling convention. I suspect that the function is using C calling convention, which would explain the unbalanced stack. I would suggest that you specify the calling convention (as #leppi suggested) in your DllImport attribute. Like this:
[DllImport("VNVAPI.dll", CallingConvention=CallingConvention.Cdecl)]
According to the Strings samples, the return value should be string:
static extern string GetGpuName(int phyGPUid);