I am using pinvoke in a project I am building.
I need to get data from a function in C, the function gets pointer to a struct.
In my c# I did a class with the appropriate attribute(layountkind.sequntial).
Before the function I do:
mystruct str=new mystruct();
str.Data=new byte[14];
func(str);
I fill the struct in the function but when it exit the function the instance of the class doesn't have the values i filled in c,i check the content of the pointer before i exit the c function and it has the right values.
Below is the prototype of the function:
[DllImport("mydll.dll", CallingConvention=CallingConvention.Cdecl)]
void func([MarshalAs(UnmanagedType.LPStruct)] mystruct str);
My struct in C#:
[StructLayout(LayoutKind.Sequential)]
public class mystruct
{
public ushort familiy;
[MatshalAs(UnmanagedType.ByValArray,SizeConst=14)]
public byte [] data;
}
function and struct in C:
struct sockaddr{
unsigned short familiy;
char data [14];
};
void func(struct sockaddr *info)
{
int i;
char buffer[100]
recvfrom(sockfd,buffer,0,info,&i);//assume i have a global varible sockfd and it is an open socket
}
How can i fix my problem?
The p/invoke declaration is incorrect. The default marshalling is In only. But you need Out marshalling. Otherwise the marshaller won't attempt to marshal the data set by the unmanaged function back to the managed class.
So you can fix the problem by declaring the function like this:
[DllImport("mydll.dll", CallingConvention = CallingConvention.Cdecl)]
static extern void func([Out] mystruct str);
Personally I think that it would be more idiomatic to use a C# struct. I'd declare it like this:
[StructLayout(LayoutKind.Sequential)]
public struct mystruct
{
public ushort family;
[MarshalAs(UnmanagedType.ByValArray, SizeConst=14)]
public byte[] data;
}
And then the function becomes:
[DllImport(dllname, CallingConvention = CallingConvention.Cdecl)]
static extern void func(out mystruct str);
And the call is simply:
mystruct str;
func(out str);
Related
I am working in C# and I need to call a function in a C++ dll library. This function returns a struct but I can´t get anything.
This is the function I need to call and the struct that returns in C++ library:
ATHENA_API _DEVICE_INFO* __stdcall GetDeviceInfoKeepConnection(_DEVICE_INFO* pDeviceInfo);
typedef struct TD_DEVICE_INFO{
TCHAR chDeviceName[256];
int nCommPort;
int nECGPos;
int nNumberOfChannel;
int nESUType;
int nTymestampType;
int nDeviceHandle;
TCHAR chDeviceID[260];
}_DEVICE_INFO;
This is my C# code trying to call the function:
[DllImport(#"\BAlertSDK\ABM_Athena.dll")]
static extern _DEVICE_INFO GetDeviceInfoKeepConnection(_DEVICE_INFO deviceInfo);
[StructLayout(LayoutKind.Sequential)]
struct _DEVICE_INFO
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
public string chDeviceName;
public int nCommPort;
public int nECGPos;
public int nNumberOfChannel;
public int nESUType;
public int nTymestampType;
public int nDeviceHandle;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
public string chDeviceID;
}
void Test_Click()
{
_DEVICE_INFO d = new _DEVICE_INFO();
_DEVICE_INFO deviceInfo = GetDeviceInfoKeepConnection(d);
}
The only I can get is an empty _DEVICE_INFO object. I think my problem is that I am not defining correctly the DEVICE INFO struct.
I have never worked with dll´s to this level. Can you help me?
Thanks in advance.
Thanks to all!! The problem has solved with this:
Parameter pass by reference and struct charset Unicode.
It seems that the function GetDeviceInfoKeepConnection returns a pointer to _DEVICE_INFO struct. So, in your C# code, you need to change the definition of the function to:
[DllImport(#"\BAlertSDK\ABM_Athena.dll")]
static extern IntPtr GetDeviceInfoKeepConnection(IntPtr deviceInfo);
And then you can access the struct data like this:
void Test_Click()
{
_DEVICE_INFO d = new _DEVICE_INFO();
IntPtr pDeviceInfo = Marshal.AllocHGlobal(Marshal.SizeOf(d));
Marshal.StructureToPtr(d, pDeviceInfo, false);
IntPtr deviceInfo = GetDeviceInfoKeepConnection(pDeviceInfo);
_DEVICE_INFO result = (_DEVICE_INFO)Marshal.PtrToStructure(deviceInfo, typeof(_DEVICE_INFO));
Marshal.FreeHGlobal(pDeviceInfo);
}
Note that, to ensure that the memory is cleaned up after use, you should use the Marshal.FreeHGlobal method to free the memory that was allocated by Marshal.AllocHGlobal.
I have a struct like this in C#:
[StructLayout(LayoutKind.Sequential, Pack = 8)]
public struct MyStruct
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 17)]
public string StringValue;
public uint IUintValue;
}
And a corresponding struct in native code
struct MyStruct
{
char StringValue[17];
ulong UintValue;
}
My goal is to pass an array of this structs from c# side to c++(native side) using pinvoke.
Here is how I use it in c#
[DllImport(#"MyLibrary.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.Cdecl)]
public static extern int SendArray([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)]ref MyStruct[] arr, int recordsCount);
and a calling code is:
var array = new MyStruct[10];
//initialize
SendArray(ref array, array.Length);
On native side I have the following function signature:
extern "C" __declspec(dllexport) int SendArray(MyStruct** Arr, int recordsCount);
And it appears o work only for the first element in array. On c++ side I get this array, but only first element is correctly marshaled. The rest of them appears to be trash.
Where is my mistake?
Your C++ code does not receive an array of structs. It receives an array of pointers to struct. Change the C++ code to be like so:
int SendArray(MyStruct* Arr, int recordsCount);
or perhaps
int SendArray(MyStruct Arr[], int recordsCount);
And then your p/invoke should be
[DllImport(...)]
public static extern int SendArray([In] MyStruct[] arr, int recordsCount);
I am also suspicious of Pack=8. Are you quite sure?
I'm trying to call functions of a C DLL.
But I got a StackOverflowException so I think something is wrong with the function as parameter.
In detail it looks like this.
C DLL (header file):
typedef struct
{
MyType aType; /* message type */
int nItems; /* number of items */
const MyItems *lpItem; /* pointer to array of items */
} MyStruct;
typedef void (__stdcall *MyCbFunc) (HWND, const MyStruct *);
API(BOOL) RegisterCbFunc (ARGS, MyCbFunc);
In C# I tried this:
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct MyStruct
{
MyType aType;
int nItems;
MyItems[] lpItem;
}
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate void CallbackDelegate(MyStruct mStruct);
[DllImport("MY.dll", CallingConvention=CallingConvention.StdCall)]
private static extern int RegisterCbFunc(IntPtr hWnd, Delegate pCB);
public static void MyCbFunc(MyStruct mStruct)
{
// do something
}
static void Main(string[] args)
{
CallbackDelegate dCbFunc = new CallbackDelegate(MyCbFunc);
int returnValue = RegisterCbFunc(IntPtr.Zero, dCbFunc);
// here, returnValue is 1
}
This runs as long until the DLL calls the callback function. Then I got an error:
An unhandled exception of type 'System.StackOverflowException' occurred in Microsoft.VisualStudio.HostingProcess.Utilities.dll
Thanks for help.
ANSWER:
I don't know why, but there was an answer which is now deleted?!
I try to recover it. The solution was to use call by reference instead of call by value for the function parameter.
public delegate void CallbackDelegate(ref MyStruct mStruct);
Your C function is expecting a pointer to a MyStruct, but you're telling the C# that it wants a pointer to a function. The difference between a function and a struct is... significant. Perhaps try something like
[DllImport("MY.dll", CallingConvention=CallingConvention.StdCall)]
private static extern int RegisterCbFunc(IntPtr hWnd, Delegate pCB);
static void Main(string[] args)
{
MyStruct mStruct;
int returnValue = RegisterCbFunc(IntPtr.Zero, mStruct);
}
If your C function is filling in the lpItem member of the MyStruct with something it allocates itself, I've got no idea what happens next, but at least it's not going to be trying to overwrite your code.
I have to call a C++ DLL from my C# program.
I'm trying to do it using PInvoke - everything works fine in VS2005\ 2008, but after migration to VS 2010, I get this exception:
PInvokeStackImbalance was detected
Message: A call to PInvoke function
'sampleFunc' 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.
This is the original C++ prototype:
typedef struct {
unsigned short field1;
unsigned short field2;
} sInfo;
_declspec(dllexport) int sampleFunc(sInfo *info, char *txt);
and here is the C# code:
[StructLayout(LayoutKind.Sequential)]
struct SInfo
{
//[MarshalAs(UnmanagedType.U1)] //also tried with the MarshalAs attr. Didn't help.
public ushort field1;
//[MarshalAs(UnmanagedType.U1)]
public ushort field2;
};
[DllImport("sampleModule.dll", CharSet=CharSet.Ansi)]
public static extern int sampleFunc(ref SInfo info, [MarshalAs(UnmanagedType.LPStr)] string txt);
I've tried it also with IntPtr instead of the ref SInfo, but got the same result...
Any help will be appreciated,
Thank you all!
Hard to see how this could have worked before. The C++ declaration doesn't declare the calling convention, the default is __cdecl unless overridden in the C++ project with the /Gz compile option. You have to tell the P/Invoke marshaller:
[DllImport("sampleModule.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern int sampleFunc(ref SInfo info, string txt);
This probably has to do with how your packing the struct. The default Pack size is 8, so its probably thinking you have too many bytes. Try setting the Pack size to 2 (16 bit aligned) and see if that helps:
[StructLayout(LayoutKind.Sequential, Pack=2)]
Alternatively you can specify the offsets like this:
[StructLayout(LayoutKind.Explicit)]
public struct struct1
{
[FieldOffset(0)]
public ushort a; // 2 bytes
[FieldOffset(2)]
public ushort b; // 2 bytes
}
Here is a good reference on packing
c# struct defined as:
[StructLayout(LayoutKind.Sequential)]
public struct RecognizeResult
{
/// float
public float similarity;
/// char*
[MarshalAs(UnmanagedType.LPStr)]
public string fileName;
}
c function signature:
void FaceRecognition(RecognizeResult *similarity); //where similarity is a pointer to an array
P/Invoke signature:
[DllImport(DllName, EntryPoint = "FaceRecognition")]
public static extern void Recognize(ref RecognizeResult similarity);
this is how i call the c++ function in managed code:
RecognizeResult[] results = new RecognizeResult[100];
Recognize(ref results[0]); //through p/invoke
it turns out the array can't be passed to unmanaged code, only the first element is passed.
how should i do to pass an array to unmanaged code (is it even possible)?
BTW, Do i have to pin the array when calling unmanaged code so that GC won't move the array?
Try this:
[DllImport(DllName, EntryPoint = "FaceRecognition")]
public static extern void Recognize(RecognizeResult[] similarity);
RecognizeResult[] results = new RecognizeResult[100];
// fill array elements
Recognize(results);