I need to pass a pointer to a structure to my DLL, any ideas how would I go about doing that?
In my C DLL:
typedef struct
{
int length;
unsigned char *value;
} Sample;
__declspec(dllexport) void __stdcall helloWorld( Sample *sample );
In my C# code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
namespace CSharpConsole
{
class Program
{
[StructLayout(LayoutKind.Sequential, Pack = 1)]
private struct Sample
{
public Int32 length;
// What Should I Declare Here?
}
[DllImport("C:\\CTestDLL.dll")]
private static extern void helloWorld( Sample sample ); // How would I make this a pointer?
void HelloWorld()
{
Sample sample = new Sample();
sample .length = 20;
// How can I fill up the values of value?
helloWorld( sample ); // How should I pass it inside here
return;
}
static void Main(string[] args)
{
Program program = new Program();
program.HelloWorld();
}
}
}
To pass a pointer to a value type into a P/Invoke function just declare the parameter as a ref or out. This implicitly takes a reference to the parameter and passes that:
[DllImport("C:\\CTestDLL.dll")]
private static extern void helloWorld(ref Sample sample);
Since your structure has an array in it, you'll have to take care to declare it properly for this to work. I strongly recommend, if possible, that you turn it into a fixed-length array, as it will make the marshaler much, much happier:
typedef struct
{
int length;
unsigned char value[MAX_LENGTH];
} Sample;
This becomes:
public struct Sample
{
int length;
[MarshalAs(UnmanagedType.LPArray, SizeConst = MAX_LENGTH)] byte[] value;
}
If that is not possible, then the runtime has no way of knowing how much data to marshal back; in that case, you probably will have to resort to manual marshaling of your data:
public struct Sample
{
int length;
IntPtr value;
}
var sample = new Sample();
helloWorld(ref sample);
byte[] value = new byte[sample.length];
Marshal.Copy(sample.value, value, 0, sample.Length);
However, based on your comment to another answer, it looks like you just need to get a block of bytes out of the C DLL into C#. For that you don't really need a structure at all, and eliminating it would simplify things a lot. If you just want to pass in an array and have it filled in and returned to you, try something like this:
(This assumes you have control over both C and C# code bases; if not then the ref suggestion is the way to accomplish what you need.)
// In C# code:
[DllImport(#"C:\CTestDll.dll")]
private static extern void helloWorld(
int length,
[MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 0)] byte[] buffer);
byte[] buffer = new byte[1024 * 8];
helloWorld(1024 * 8, buffer);
// In C:
__declspec(dllexport) void __stdcall helloWorld(int, unsigned char *);
void helloWorld(int cb, unsigned char *buf)
{
memcpy(buf, DATASRC, cb);
}
In C, an unsigned char is, by definition, the same size as a C# byte - 8 bits, no sign. In C#, a char is actually two bytes. The runtime will automatically "convert" an unsigned char * to a byte[] for you. (There's not really a conversion at all; they are just different names for the same type.)
Default Marshaling for Value Types - gives some information on marshalling structs.
Calling Win32 DLLs in C# with P/Invoke - a little over half way down the page there's a table showing the type conversions between the standard unmanaged and managed types.
There are a few ways to pass around and convert the types.
As Michael Edenfield pointed out you can generally just use the ref keyword to indicate that a parameter should by passed by reference which is basically a pointer.
However sometimes things don't cooperate, particularly when it comes to strings or complex data types so this is where the IntPtr type comes in.
You have a couple of options for using IntPtrs.
You can create an IntPtr to a block of unmanaged memory of a specified size using:
IntPtr pointer = Marshal.AllocHGlobal(sizeOfBufferInBytes);
//Do stuff with the pointer
Marshal.FreeHGlobal(pointer); //Don't forget to release the memory
This is obviously a bit dangerous because you're manually allocating unmanaged memory.
You'll need to Marshal the data from the buffer back into a managed type, using something like Marshal.Copy(), Marshal.PtrToStructure(), Buffer.BlockCopy(), etc.
Alternatively you can create a managed object and pin it in memory while you need to, get a pointer to it and pass that to your method.
MyObject instance = new MyObject();
GCHandle gch = GCHandle.Alloc(instance, GCHandleType.Pinned);
importedMethod(gch.AddrOfPinnedObject()); //AddrOfPinnedObject() gives you an IntPtr
gch.Free(); //Release the pinned memory so the garbage collector can deal with it
This avoids the necessity for manually marshalling back to the correct data type but this is not always an option depending on the type of MyObject and whether it's blittable.
This works for me:
DLL:
typedef struct
{
int length;
unsigned char *value;
} Sample;
extern "C" __declspec(dllexport) void __stdcall helloWorld( Sample *sample )
{
MessageBoxA(NULL, (LPCSTR) sample->value, (LPCSTR) sample->value, 0);
}
C#:
class Program
{
[StructLayout(LayoutKind.Sequential, Pack = 1)]
private class Sample
{
public Int32 length;
public String value;
}
[DllImport("C:\\Users\\Kep\\Documents\\Visual Studio 2010\\Projects\\SODLL\\Debug\\DLL.dll")]
private static extern void helloWorld(Sample sample);
static void Main(string[] args)
{
Sample s = new Sample();
s.length = 10;
s.value = "Huhu";
helloWorld(s);
}
}
Important thing is to mark it as a class, not a struct in C#.
With this, you could also use constructors etc. in C#:
class Program
{
[StructLayout(LayoutKind.Sequential, Pack = 1)]
private class Sample
{
public Int32 length;
public String value;
public Sample(String s)
{
length = s.Length;
value = s;
}
}
[DllImport("C:\\Users\\Kep\\Documents\\Visual Studio 2010\\Projects\\SODLL\\Debug\\DLL.dll")]
private static extern void helloWorld(Sample sample);
static void Main(string[] args)
{
Sample s = new Sample("Huhu");
helloWorld(s);
}
}
Related
I have a Unity5 program that is using a common structure (smMsg) to send data from a C++ DLL into C#.
The structure contains an array:
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
public float[] mtx;
This array is to be considered as a 4x4 Matrix, hence the constant size of 16.
The program works, receiving data into the C# corresponding structure; however, it seems that from my array I am missing the first element (mtx[0]) each time I run the program. It seems every other element has shifted to the left with an extra 0 for the last element, maintaining the sequential order they are to be in.
I considered it to be because of the UnmanagedType I was using, however other sources tell me that UnmanagedType.ByValArray is the correct type.
Would anyone have a direction or lead I can follow to help solve this problem?
Process of Copying Data
C#:
// DLL Import
[DllImport(DLL_NAME, EntryPoint = "smCopy")]
private static extern void smCopyData(IntPtr dest, IntPtr len); //const VOID *dest, SIZE_T len);
// Copying data logic
{
// allocate intptr to buffer
var len = Marshal.SizeOf(typeof(smMsg));
IntPtr msg_intptr = Marshal.AllocHGlobal(len);
try
{
// Copy data
smCopyData(msg_intptr, (IntPtr)(len));
// Set POINTER data to struct
return_msg = (smMsg)Marshal.PtrToStructure(msg_intptr, typeof(smMsg));
}
finally
{
// free unmanaged memory!
Marshal.FreeHGlobal(msg_intptr);
}
}
C++
// Function called via DLL
void DLL_API smCopy(const VOID *dest, SIZE_T len)
{
CopyMemory((PVOID)(dest), (PVOID)(mapBuffer), len);
}
Struct Definition
The main piece of data I am interested in is float[] mtx
[StructLayout(LayoutKind.Sequential)]
public struct smMsg
{
public smHeader header;
public smData data;
}
[StructLayout(LayoutKind.Sequential)]
public struct smData
{
// Event ID.
public int evtId;
public int status;
// Floating point values. Actual data to be transmitted.
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
public float[] mtx;
}
[StructLayout(LayoutKind.Sequential)]
public struct smHeader
{
public ushort chkSum;
public char numWords;
public char msgType;
}
UPDATE 2/29
Thanks to #Zastai, I ended up able to recover the missing element. As it turns out, I wanted to be using "byte" as the data type instead of char, as char is a C# unicode type (short).
What I ended up doing is changing my smHeader as:
[StructLayout(LayoutKind.Sequential)]
public struct smHeader
{
public ushort chkSum;
public byte numWords;
public byte msgType;
}
.. which in turn lowered the smHeader size from 6 to 4, setting the smMsg struct size equal in terms of both C# & C++.
Thanks to #Zastai for helping out a ton.
Turns out that when using char in C++ for a struct, it's C# counterpart is a byte. This resolved the difference in structure size between C# & C++. Because of this error, the smMsg struct in C# allocated more memory than it needed.
The question is updated with the new smHeader definition.
I have a C++ DLL (SimpleDLL.dll), with a exposed function (DllFunctionPoibnterGetName) that has a function pointer (getNameFP). The function pointer takes a char * as a parameter (*char * name*).
// C++
DllExport void DllFunctionPoibnterGetName( void (*getNameFP) (char * name, unsigned short * length ) ) {
char name[1024];
unsigned short length = 0 ;
getNameFP( name, &length );
printf( "length=[%d] name=[%s]\n", length, name );
}
I have a C# application that would like to use this C++ DLL.
// C#
public unsafe delegate void GetName( System.Char* name, System.UInt16* length);
unsafe class Program
{
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void delegateGetName(System.Char* name, System.UInt16* length);
[DllImport("SimpleDLL.dll", CharSet = CharSet.Ansi )]
public static extern void DllFunctionPoibnterGetName([MarshalAs(UnmanagedType.FunctionPtr)] delegateGetName getName);
static void Main(string[] args)
{
DllFunctionPoibnterGetName(GetName);
}
static void GetName(System.Char* name, System.UInt16* length)
{
// name = "one two three";
*length = 10;
}
}
Currently I can set the length with out any problems, but I can't seem to find a way to set the name correctly.
My Question is
How do I set the char * name to a value correctly.
You don't need to use unsafe code. You can do it like this:
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void delegateGetName(IntPtr name, out ushort length);
....
static void GetName(IntPtr name, out ushort length)
{
byte[] buffer = Encoding.Default.GetBytes("one two three");
length = (ushort)buffer.Length;
Marshal.Copy(buffer, 0, name, buffer.Length);
}
Although this interface design is just asking for a buffer overrun. How are you supposed to know how big the unmanaged buffer is? It would make more sense for the length parameter to be passed by ref. On input it would tell you how big the buffer is. On output you would have recorded how many bytes you copied into the buffer.
Cast the char* as a char[]. That should do the trick.
Casting the char will not do. The char * data is 'unmanaged', native data. And C# uses 'managed', .NET data.
You need to make a wrapper for your call and use marschall to convert the data from 'unmanaged' to 'managed'.
I have searched for days and have tried everything I could find, but still cannot get this to work.
Details:
I have a 3rd party stock trading app that is calling into my unmanaged dll. It is supplying data that the dll processes/filters and then saves into a global ring buffer. The ring buffer is an array of structures, 100 long. All of this runs in the stock trading apps process.
I also have a managed C# app calling into the same dll in a different process that needs to get the info in the global ring buffer as quickly and efficiently as possible. Everything works except that I can only get data for the first structure in the array. Also after the call to the dll from C# the C# code no longer knows that arrayMD is an array of structs, it shows up in the debugger as a simple structure. Could it be the memcpy in the dll causing the problem? I’ve tried all kinds of combinations with [In, Out], IntPtr, and Marchal.PtrToStructure combinations. I am greatly fubar. Any help would be greatly appreciated.
Thanks
Here is what I am attempting.
On the dll side:
struct stMD
{
float Price;
unsigned int PriceDir;
unsigned int PriceDirCnt;
};
// Global memory
#pragma data_seg (".IPC")
bool NewPoint = false; // Flag used to signal a new point.
static stMD aryMD [100] = {{0}};
#pragma data_seg()
void __stdcall RetrieveMD (stMD *LatestMD [])
{
memcpy(*LatestMD, aryMD, sizeof(aryMD));
}
On the C# side:
[StructLayout(LayoutKind.Sequential)]
public struct stMD
{
public float Price;
public uint PriceDir;
public uint PriceDirCnt;
};
public static stMD[] arrayMD = new stMD[100];
[DllImport(#"Market.dll")]
public static extern void RetrieveMD(ref stMD[] arrayMD);
RetrieveMD(ref arrayMD);
The problem is the definition of your DLL entry point:
void __stdcall RetrieveMD (stMDP *LatestMD [])
You don't specify the size of the array, so how is C# supposed to know how many elements were copied into it? This is a problem in other languages too. Your implementation simply assumes that the provided memory is large enough to contain aryMD. But what if it's not? You've just created a buffer overrun.
If you want the caller to allocate the array, then the caller must also pass in the number of elements that the array contains.
Edit
The C++ declaration should look something like this:
// On input, length should be the number of elements in the LatestMD array.
// On output, length should be the number of valid records copied into the array.
void __stdcall RetrieveMD( stMDP * LatestMD, int * length );
The C# declaration would then look something like this:
[DllImport(#"Market.dll")]
public static extern void RetrieveMD(
[In, Out, MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)] ref stMD[] arrayMD,
[In, Out] ref int length);
Your problem, I think, is that you are trying to pass an array by reference from C# into C, and you almost never need to do that. In your case, all you want to happen is for C# to allocate memory for 100 of your structures, then pass that memory to C to be filled in. In your case, you're passing a pointer to an array of structures, which is an extra level of indirection that you don't really need.
You rarely see C functions that take a fixed sized array; instead, your function would typically be defined in C to accept a pointer and a length, e.g. something like:
void __stdcall RetrieveMD (stMDP *LatestMD, int size)
{
int count = 0;
if (size < sizeof(aryMD))
count = size;
else
count = sizeof(aryMD);
memcpy(LatestMD, aryMD, count);
}
To call this method from C#, you need to do two things. First, you need to allocate an array of the appropriate size to pass in. Second, you need to tell the marshaling code (that does the C# -> C copying) how to figure out how much data to be marshaled, via the [MarshalAs] attribute:
[DllImport(#"Market.dll")]
public static extern void RetrieveMD (
[MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] stMDP[] arrayMD,
int length
);
var x = new stMDP[100];
RetrieveMD(x, 100);
I got it working. Was I ever tring to make this harder than it is.
I re-read chapter 2 of ".NET 2.0 Interoperability Recipes: A Problem-Solution Approach".
Here's what works.
On C++ side I removed the pointers
struct stMD
{
float Price;
unsigned int PriceDir;
unsigned int PriceDirCnt;
};
// Global memory
#pragma data_seg (".IPC")
bool NewPoint = false; // Flag used to signal a new point.
static stMD aryMD [100] = {{0}};
#pragma data_seg()
void __stdcall RetrieveMD (stMD LatestMD [100])
{
memcpy(LatestMD, aryMD, sizeof(aryMD));
}
On the C# side I removed both (ref)s and added [In, Out]
[StructLayout(LayoutKind.Sequential)]
public struct stMD
{
public float Price;
public uint PriceDir;
public uint PriceDirCnt;
};
public static stMD[] arrayMD = new stMD[100];
[DllImport(#"Market.dll")]
public static extern void RetrieveMD([In, Out] stMD[] arrayMD);
RetrieveMD(arrayMD);
Thanks to everyone who offered help.
There appears to be multiple ways to do this, but the examples I've tried haven't worked for me.
I read somewhere that using unsafe pointers would be the way to go for more complex structures that require pointers. (sorry but I haven't been able to find the source again)
My latest attempt looks something like this:
unsafe public struct ComplexStruct {
public Int32 NumSubStruct;
public SubStruct*[] arr;
}
unsafe public static extern UInt32 DLL_Call(ref ComplexStruct p);
function {
unsafe {
ComplexStruct p = new ComplexStruct();
p.NumSubStruct = 2;
p.arr= new SubStruct*[p.NumSubStruct];
SubStruct p1 = new SubStruct();
SubStruct p2 = new SubStruct();
p.arr[0] = &p1;
p.arr[1] = &p2;
testLogHandlerHandle = DLL_Call(ref p);
}
}
I get an error which says that SubStruct cannot be marshaled (Signature is not interop compatible).
Is it possible to pass the object without marshaling? (the DLL should be loaded in the same process space as the C# application).
If not, what would be the simplest way to pass a copy of the object?
Note: changing the DLL is a non-issue. I am vaguely aware of some other solutions, such as C++/CLI, but I only have a relatively small number of structure types that need to be passed in such a way.
EDIT:
A few notes:
The array needs to by dynamic
The actual structs a bit more complicated (there's 4 layers of nested structures like this) so I think adding them would detract from the question, but for completeness, here is how I would declare these in C++:
struct ComplexStruct {
unsigned int NumSubStruct;
SubStruct** arr;
};
struct SubStruct {
unsigned int NumSubStruct;
//some more datamembers here as well
SubSubStruct** arr;
};
(the extra indirection isn't necessary, but I figured it might be useful to be able to declare the array of SubStruct pointers as IntPtrs)
Like this maybe?
unsafe public struct ComplexStruct
{
public Int32 NumSubStruct;
public SubStruct** arr;
}
unsafe static void Main(string[] args)
{
ComplexStruct p = new ComplexStruct();
p.NumSubStruct = 2;
SubStruct[] s = new SubStruct[p.NumSubStruct];
// no need to new here, valuetype array
s[0].value = 1;
s[1].value = 2;
fixed (SubStruct* sp = s)
fixed (SubStruct** spp = new SubStruct*[] { sp })
{
p.arr = spp;
testLogHandlerHandle = DLL_Call(ref p);
}
}
You should use something like this and this.
[StructLayout(LayoutKind.Sequential)]
public struct ComplexStruct
{
public Int32 NumSubStruct;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = MAX_NO_SUB_STRUCTS)]
public SubStruct[] arr;
}
public static extern UInt32 DLL_Call(IntPtr p);
Then marshal it with something like this:
IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(ComplexStruct)));
try
{
// Copy the struct to unmanaged memory.
Marshal.StructureToPtr(p, ptr, false);
testLogHandlerHandle = DLL_Call(ptr);
}
finally
{
// Free the unmanaged memory.
Marshal.FreeHGlobal(ptr);
}
Try to get rid of all the unsafe stuff, I doubt its necessary!
I am porting a c++ code into c#.There are 2 structures, as explained
below.
// Must be a total of 180 bytes
typedef struct MAINTENANCE_PARAM`
{
BYTE bCommand;
BYTE bSubCommand;
USHORT usDataLength;
union // Must be no larger than 176 bytes
{
MyStruct1 myStruct1;
MyStruct2 myStruct2;
BYTE bDummy[176];
} data;
} MAINTENANCE_PARAM;
typedef struct _OCI_PARAM {
SHORT sType; // Size: 2
LONG lValue; // 4
SHORT sScale; // 2
LONG lValueTabIdx; // 4
} OCI_PARAM[OCI_MAXPARAM]; //Size: OCI_MAXPARAM = 15 // 15 * 12 = 180
My code uses the memcpy in the following fashion.
MAINTENANCE_PARAM maintainanceParam;
OCI_PARAM ociParam
// Copy recieved structure to correct format
memcpy((void*)& maintainanceParam, (void*) ociParam, sizeof(OCI_PARAM));
As I know there is no code for memcpy in the C#. So how can I port the
above code into the C#. I am new to C#. I don't know much regarding
the C#. So can anybody tell me how exactly I can implement the above
line of code in C#. I need to copy 180 bytes from one structure to another structure object with different datatype
Thanks in Advance for any help.
Regards,
Ashish
Use the StructLayoutAttribute and FieldOffsetAttribute for your structs so that you can layout your fields explicitly, then import RtlMoveMemory (P/Invoke). You can modify the signature to take any pointer type (in unsafe context) or use the standard signature on PInvoke.net.
unsafe class Program {
[System.Runtime.InteropServices.DllImport("Kernel32.dll", EntryPoint = "RtlMoveMemory", SetLastError = false)]
private static extern void MoveMemory(void* dest, void* src, int size);
static void Main(string[] args) {
Maintenance_Param p1 = new Maintenance_Param();
p1.bCommand = 2;
p1.bSubCommand = 3;
p1.usDataLength = 3;
p1.myStruct1 = new MyStruct1();
Maintenance_Param p2 = new Maintenance_Param();
MoveMemory(&p2, &p1, sizeof(Maintenance_Param));
}
}
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Explicit)]
public struct Maintenance_Param {
// fields should be private and be accessed over properties ...
[System.Runtime.InteropServices.FieldOffset(0)]
public byte bCommand;
[System.Runtime.InteropServices.FieldOffset(1)]
public byte bSubCommand;
[System.Runtime.InteropServices.FieldOffset(2)]
public ushort usDataLength;
[System.Runtime.InteropServices.FieldOffset(4)]
public MyStruct1 myStruct1;
[System.Runtime.InteropServices.FieldOffset(4)]
public MyStruct2 myStruct2;
}
public struct MyStruct1 {
int value;
}
public struct MyStruct2 {
int value;
}
MemCpy DOES exist in .NET! Try googling for OpCodes.Cpblk. Here is an example: http://www.abstractpath.com/weblog/2009/04/memcpy-in-c.html