quadrille01
asked on
questing about porting C to C#, dllimport, and probably something about marshalling
Hey folks,
Here's the situation. I've got a C dll, and I want to call the functions in it from a C# app. I can call these functions, but they don't behave the same when called from a C# program as they do when called from a C app. I'm having a problem with one in particular, PeekRequest(). Here's how its called in the C program:
int set_channel( int channel )
{
unsigned long reqdata[139];
OVERLAPPED iodata;
memset( (void *) reqdata, 0, sizeof( reqdata ) );
memset( (void *) &iodata, 0, sizeof( iodata ) );
iodata.hEvent = CreateEvent( 0, 0, 0, 0 );
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (unsigned long) &channel;
reqdata[8] = 4;
return( PeekRequest( hAdapter, reqdata, &iodata ) );
}
The prototype of this function is:
HANDLE PeekRequest(HANDLE,void *,OVERLAPPED);
Here's the same function in my C# program. I first import the dll with:
[DllImport("Peek.dll")]
public static extern IntPtr PeekRequest
(IntPtr netcrudAdapter,
uint[] reqdata,
System.Threading.NativeOve rlapped iodata);
and import the CreateEvent function:
//Win32 API call for which no C# equivalent exists
[DllImport("kernel32.dll", SetLastError=true)]
static extern IntPtr CreateEvent(IntPtr lpEventAttributes,
bool bManualReset, bool bInitialState,
[MarshalAs(UnmanagedType.L PStr)] String lpName);
private long set_channel(uint channel)
{
//array of unsigned integers
uint[] reqdata = new uint[139];
//C# version of OVERLAPPED type
System.Threading.NativeOve rlapped iodata;
//Initialize array
for (int i = 0; i < 139; i++)
reqdata[i] = 0;
//TODO - may need to initialize iodata
iodata.EventHandle = IntPtr.Zero;
iodata.InternalHigh = IntPtr.Zero;
iodata.InternalLow = IntPtr.Zero;
iodata.OffsetHigh = 0;
iodata.OffsetLow = 0;
iodata.EventHandle = CreateEvent(IntPtr.Zero, false, false, string.Empty);
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (uint)&channel;
reqdata[8] = 4;
return((long)PeekRequest(n etcrudAdap ter, reqdata, iodata));
}
Still with me? Excellent. So here's the meat of the problem. The C function returns 0 for a given channel, which is good. The same function in C# returns 87, which is garbage. Any advice?
Much thanks,
Nathan King
Here's the situation. I've got a C dll, and I want to call the functions in it from a C# app. I can call these functions, but they don't behave the same when called from a C# program as they do when called from a C app. I'm having a problem with one in particular, PeekRequest(). Here's how its called in the C program:
int set_channel( int channel )
{
unsigned long reqdata[139];
OVERLAPPED iodata;
memset( (void *) reqdata, 0, sizeof( reqdata ) );
memset( (void *) &iodata, 0, sizeof( iodata ) );
iodata.hEvent = CreateEvent( 0, 0, 0, 0 );
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (unsigned long) &channel;
reqdata[8] = 4;
return( PeekRequest( hAdapter, reqdata, &iodata ) );
}
The prototype of this function is:
HANDLE PeekRequest(HANDLE,void *,OVERLAPPED);
Here's the same function in my C# program. I first import the dll with:
[DllImport("Peek.dll")]
public static extern IntPtr PeekRequest
(IntPtr netcrudAdapter,
uint[] reqdata,
System.Threading.NativeOve
and import the CreateEvent function:
//Win32 API call for which no C# equivalent exists
[DllImport("kernel32.dll",
static extern IntPtr CreateEvent(IntPtr lpEventAttributes,
bool bManualReset, bool bInitialState,
[MarshalAs(UnmanagedType.L
private long set_channel(uint channel)
{
//array of unsigned integers
uint[] reqdata = new uint[139];
//C# version of OVERLAPPED type
System.Threading.NativeOve
//Initialize array
for (int i = 0; i < 139; i++)
reqdata[i] = 0;
//TODO - may need to initialize iodata
iodata.EventHandle = IntPtr.Zero;
iodata.InternalHigh = IntPtr.Zero;
iodata.InternalLow = IntPtr.Zero;
iodata.OffsetHigh = 0;
iodata.OffsetLow = 0;
iodata.EventHandle = CreateEvent(IntPtr.Zero, false, false, string.Empty);
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (uint)&channel;
reqdata[8] = 4;
return((long)PeekRequest(n
}
Still with me? Excellent. So here's the meat of the problem. The C function returns 0 for a given channel, which is good. The same function in C# returns 87, which is garbage. Any advice?
Much thanks,
Nathan King
Before learning this PInvoke stuff, I want to ask general question: why don't you use C++/CLI for this? If you know both C and C#, you can easily do this with C++/CLI instead of writing these ugly PInvoke declarations.
Advantage of C++/CLI is that it allows to call unmanaged functions directly from managed code. You need to write wrapper C++/CLI class library which exposes pure managed interface to C# client, and internally calls unmanaged functions.
If you don't want to work with C++/CLI, I will try to find the problem in this code.
Advantage of C++/CLI is that it allows to call unmanaged functions directly from managed code. You need to write wrapper C++/CLI class library which exposes pure managed interface to C# client, and internally calls unmanaged functions.
If you don't want to work with C++/CLI, I will try to find the problem in this code.
ASKER
Why use all C#? Well, the biggest reason is that it seemed like a good idea at the time. And now that I've spent this much time on it I'd like to just keep on this path if I can. There are a couple functions from this dll that behave using PInvoke declarations. I suspect my problem is mismatching my managed and unmanaged types when going from C to C#.
I'm certainly not averse to switching to C++/CLI if thats what it comes to.
Nathan
I'm certainly not averse to switching to C++/CLI if thats what it comes to.
Nathan
Well, let's look at PInvoke stuff.
static extern IntPtr CreateEvent(IntPtr lpEventAttributes,
bool bManualReset, bool bInitialState,
[MarshalAs(UnmanagedType.L PStr)] String lpName);
bool parameters don't match BOOL type - change to int.
Replace last parameter type with IntPtr and pass IntPtr.Zero.
reqdata[7] = (uint)&channel;
Allocate ubnmanaged memory block using Marshal.AllocHGlobal, copy channel value to it using Marshal.WriteInt32. Marshal.AllocHGlobal returns IntPtr. Convert it to int using ToInt32 method, and assign to reqdata[7]. Notice that C# long is 64-bits value. I guess that PeekRequest excpects 32 bits, replace with int.
C# PeekRequest definition.
Replace reqdata parameter type with IntPtr. Allocate unmanaged memory block using Marshal.AllocHGlobal, fill it using Marshal.Copy.
return((long)PeekRequest(n etcrudAdap ter, reqdata, iodata));
Replace return value with IntPtr.ToInt32.
If you have PeekRequest source code, debug it to see parameter values.
PInvoke sucks (side note).
static extern IntPtr CreateEvent(IntPtr lpEventAttributes,
bool bManualReset, bool bInitialState,
[MarshalAs(UnmanagedType.L
bool parameters don't match BOOL type - change to int.
Replace last parameter type with IntPtr and pass IntPtr.Zero.
reqdata[7] = (uint)&channel;
Allocate ubnmanaged memory block using Marshal.AllocHGlobal, copy channel value to it using Marshal.WriteInt32. Marshal.AllocHGlobal returns IntPtr. Convert it to int using ToInt32 method, and assign to reqdata[7]. Notice that C# long is 64-bits value. I guess that PeekRequest excpects 32 bits, replace with int.
C# PeekRequest definition.
Replace reqdata parameter type with IntPtr. Allocate unmanaged memory block using Marshal.AllocHGlobal, fill it using Marshal.Copy.
return((long)PeekRequest(n
Replace return value with IntPtr.ToInt32.
If you have PeekRequest source code, debug it to see parameter values.
PInvoke sucks (side note).
ASKER
Hey, thanks for the reply.
I've changed most of what you suggested. I can't allocate reqdata using Marshal.AllocHGlobal, since I need an unsigned int for element 6. Is there an unsigned equivalent?
"If you have PeekRequest source code, debug it to see parameter values."
Would that I did, my friend.
"PInvoke sucks (side note)."
Yeah, I'm getting that. I'm a hair's breadth from the more-trouble-than-its-wort h stage. It may be time go ahead and switch over to C++/CLI for handling the dll functions.
I've changed most of what you suggested. I can't allocate reqdata using Marshal.AllocHGlobal, since I need an unsigned int for element 6. Is there an unsigned equivalent?
"If you have PeekRequest source code, debug it to see parameter values."
Would that I did, my friend.
"PInvoke sucks (side note)."
Yeah, I'm getting that. I'm a hair's breadth from the more-trouble-than-its-wort
If you can debug PeekRequest, you can see what parameters are wrong.
I give you short translation of most tricky part, I hope this can give you idea how to prepare unmanaged memory for API. Managed data is kept in manaded memory. Unmanaged data for API should be marshaled to unmanaged memory. For simple parameters like int, char, string, PInvoke generates default marshalling. We need only declare function prototype correctly. For non-trivial parameters we can allocate unmanaged memory blocks and fill them using Marshal functions. They have all we need, every C++ programmer can use them.
int set_channel( int channel )
{
unsigned long reqdata[139]; // we use int for this - the same size
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (unsigned long) &channel;
reqdata[8] = 4;
PeekRequest( ..., reqdata, ...) ); // declare reqdata as IntPtr for C#
}
IntPtr channelPtr = Marshal.AllocHGlobal(Marsh al.SizeOf( typeof(int )));
Marshal.WriteInt32(channel Ptr, channel); // channel in unmanaged memory
IntPtr reqdata = Marhal.AllocHGlobal(Marsha l.SizeOf(t ypeof(int) ), 139);
Marhal.WriteInt32(reqdata, 5, 1);
Marhal.WriteInt32(reqdata, 6, 0xFF636713); // will be OK
Marshal.WriteInt32(reqdata , 7, channelPtr.ToInt32()); // write pointer to channel in unmanaged memory
Marhal.WriteInt32(reqdata, 8, 4);
PeekRequest( ..., reqdata, ...) );
// read output if required
Marhal.FreeHGlobal(channel Ptr);
Marhal.FreeHGlobal(reqdata );
I think that System.Threading.NativeOve rlapped iodata parameter must be passed as ref. By default structure it is marshalled by value.
I give you short translation of most tricky part, I hope this can give you idea how to prepare unmanaged memory for API. Managed data is kept in manaded memory. Unmanaged data for API should be marshaled to unmanaged memory. For simple parameters like int, char, string, PInvoke generates default marshalling. We need only declare function prototype correctly. For non-trivial parameters we can allocate unmanaged memory blocks and fill them using Marshal functions. They have all we need, every C++ programmer can use them.
int set_channel( int channel )
{
unsigned long reqdata[139]; // we use int for this - the same size
reqdata[5] = 1;
reqdata[6] = 0xFF636713;
reqdata[7] = (unsigned long) &channel;
reqdata[8] = 4;
PeekRequest( ..., reqdata, ...) ); // declare reqdata as IntPtr for C#
}
IntPtr channelPtr = Marshal.AllocHGlobal(Marsh
Marshal.WriteInt32(channel
IntPtr reqdata = Marhal.AllocHGlobal(Marsha
Marhal.WriteInt32(reqdata,
Marhal.WriteInt32(reqdata,
Marshal.WriteInt32(reqdata
Marhal.WriteInt32(reqdata,
PeekRequest( ..., reqdata, ...) );
// read output if required
Marhal.FreeHGlobal(channel
Marhal.FreeHGlobal(reqdata
I think that System.Threading.NativeOve
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ASKER
Thanks Alex, I imagine I can take it from here. I've got to switch to C++/CLI, if for no other reason than that there appears to be no mechanism for writing an unsigned int into unmanaged memory. I've tried a hundred different ways of doing
Marhal.WriteInt32(reqdata, 6, 0xFF636713);
but the compiler says no.
Thanks again.
Marhal.WriteInt32(reqdata,
but the compiler says no.
Thanks again.
Marshal.WriteInt32(reqdata , 6, unchecked((int)0xFF636713) );
How about using reflection in this case?
--anv