Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll - C# Discussion Boards

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 3:14

Hi,

I'm trying to communicate with an unmanaged c++ dll from c# that takes two 2d
float arrays, one as input with data in it and the other will have the
result of the operation in it as follows:

bool Evaluate(float** input,float** output,int nFrames, int
featureWidth);

note: nFrames and featureWidth will determine the sizes of input and
output arrays in the c++ code.

Using this method in c# requires you to use float multidimensional
arrays. However I keep on getting exceptions thrown by the dll while
the same code works fine in a normal console application!

Trying to debug the dll as much as i can i figured out that the arrays
are not being passed correctly. can anybody help me out here, how
would I pass a 2 dimentional array to unmanaged c++ function?

Thanks
Fahd

m@u11-Dec-07 3:25

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 3:25

Hi
how did you define the Call in c# (any MarshalAs usage or something..?)

what kind of exceptions do you get? access violations or others..?

f4hd wrote:
dll while
the same code works fine in a normal console application!

do you mean you have a c# console application that successfully handles the dll?

greets
m@u

f4hd11-Dec-07 3:46

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 3:46

Hi M@u

thanks for the reply.

here is my definition

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, float[,] output, int nFrames,int featureWidth);

in unmanaged c++ it is
bool xyz_MFCApp::Evaluate(float** input, float **output,int nFrames,int featureWidth);

The exception that I get is System.NullReferenceException. Which is access violation I assume.

>>do you mean you have a c# console application that successfully handles the dll?
I have a legacy c++ code that im making into a dll in order to use it with c#
wen accessed using a c++ console app the code works fine. but wen i convert the code into a dll and use the exposed function in c# it throws the exception i just mentioned. on further investigating i figured out its the problem with the passing of 2d float arrays.
so if i pass the input array and access the first row i.e input[0][0] in the dll its fine but when i access input[1][0] the exception is thrown!
Thus i think i need to find out the correct way to pass the 2d array such that the memory it holds isnt affected.

hope I havent confused things further Smile | :)

Fahd

m@u11-Dec-07 4:15

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 4:15

f4hd wrote:
The exception that I get is System.NullReferenceException. Which is access violation I assume

No the Null Reference exception only says that you're passing a parameter that is null and is not supposed to be null

f4hd wrote:
[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, float[,] output, int nFrames,int featureWidth);

that with the multi-dimensional arrays might be a big problem.. i read something about it once and i think the central statement there was, that passing multi-dimensional arrays is not supported / only possible by using dirty tricks..

what you could try would be to mark the output array as ref or out.

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, [In,Out] ref float[,] output, int nFrames, int featureWidth);

[DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(float [,] input, [Out] out float[,] output, int nFrames, int featureWidth);

i find it a bit strange that nFrames is not a pointer, do you decide how many entrys per dimension the dll will return?

f4hd11-Dec-07 8:33

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 8:33

>No the Null Reference exception only says that you're passing a parameter that is null and is not >supposed to be null
well data is passed but incorrectly. see I can access the first row of the 2d array but not any other.

mebe you are right its not supported so one way, not quite elegant, is to convert the 2d arrays into 1d arrays during passing and receiving... Can there be any better way I wonder?

the In and out dont help much because of the same issue i mentioned above.

>>i find it a bit strange that nFrames is not a pointer, do you decide how many entrys per dimension >>the dll will return?

Yes I know it from before and is fixed for this Dll call and using it I do know the dimensions being returned

m@u11-Dec-07 22:33

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

11-Dec-07 22:33

f4hd wrote:
not quite elegant, is to convert the 2d arrays into 1d arrays during passing and receiving... Can there be any better way I wonder?

well if you can make it work that way i think that's a good way. an other way you could try would be to pass an array of intptrs that point each to an array of float.
it's ugly and i don't really know if it'll work at all but it *might* work Smile | :)

that it would look like this:

DllImportAttribute(@".\xyz_MFC.dll")]
public static extern bool Evaluate(IntPtr [] input, IntPtr[] output, int nFrames,int featureWidth);
private float[,] foo()
{
    int nFrames = 3; // change these 2 values to appropriate vals
    int featurWidth = 5; // ...
    float[,] myArray = new float[2,nFrames];
    // fill your values here...
    IntPtr[] input = writeArray(myArray);
    IntPtr[] output = allocArray(featurWidth);
    bool ok = Evaluate(input, output, nFrames, featurWidth);
    freeArray(input);
    return readArray(output,featurWidth);
}
private float[,] readArray(IntPtr[] Items, int featureWidth)
{
    float[,] RetVal = new float[2,featureWidth];
    readMemArray(Items[0],RetVal,0,featureWidth);
    readMemArray(Items[1],RetVal,1,featureWidth)
    freeArray(Items);
    return RetVal;
}
private void readMemArray(IntPtr Pointer, Float[,] Target, int Dimension, int featureWidth)
{
   float[] Dummy = new float[featureWidth];
   Marshal.Copy(Pointer,Dummy,0,featureWidth);
   copyArray(Dummy, Target, Dimension);
}
private void freeArray(IntPtr[] Items)
{
    Marshal.FreeHGlobal(Items[0]);
    Marshal.FreeHGlobal(Items[1]);
}
private IntPtr[] allocArray(int ItemCount)
{
    IntPtr RetVal = new IntPtr[2];
    int Count = Marshal.SizeOf(typeof(float)) * ItemCount;
    RetVal[0] = Marshal.AllocHGlobal(Count);
    RetVal[1] = Marshal.AllocHGlobal(Count);
    return RetVal;
}
private IntPtr[] writeArray(float[,] Array)
{
    IntPtr[] RetVal = allocArray(Array.GetLength(1));
    float[] Dummy = new float[Array.GetLength(1)];
    copyArray(Array, Dummy, 0);
    Marshal.Copy(Dummy,0,RetVal[0],Dummy.Length);
    copyArray(Array, Dummy, 1);
    Marshal.Copy(Dummy,0,RetVal[1],Dummy.Length);
}
private void copyArray(float[] Source, float[,] Destination, int zDimIndex)
{
    for(int i = 0; i< Source.Length; i++)
    {
        Destination[zDimIndex,i] = Source[i];
    }
}
private void copyArray(float[,] Source, float[] Destination, int zDimIndex)
{
    for(int i = 0; i < Destination.Length; i++)
    {
        Destination[i] = Source[zDimIndex,i];
    }
}

the code is untested so maybe you'll have to change something but generally it could work.
however.. if you can make it work with an 1-dimensional array do it that way Smile | :)

greets
m@u

f4hd13-Dec-07 4:23

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

13-Dec-07 4:23

Thanks a lot for the code m@u

I havent tried it yet but I have tried the 2D to 1D method which worked as expected. I am worried about the speed impact of this method as it will be called many times and each time there is this conversion, its going to be slow. So if you can comment about the speed impact of the code you've mention in comparison to it that will be great.
Typical values of arrays will be something like 5000x40 and this dll will be called about a 1000 times! so if you think using Intptr might be quicker please let me know. Thanks

m@u13-Dec-07 5:02

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

13-Dec-07 5:02

Hi
i don't really know because i didn't thest the posted code but i think the conversion will be quite slow for such big arrays and since you can make it work with the 2d to 1d conversion i'd say keep it like that.

greets
m@u

Skippums11-Dec-07 9:02

Skippums

11-Dec-07 9:02

Ok, here are a few ideas for you to try:

1. Change the C# import declaration type from float[,] to float[][] (they are NOT equivalent types)
2. Change the C++ method signiture to take parameters of type float[][] instead of float**
3. Convert the float[][] to a float[] in your c# code, and change your method to either float* or float[] in your C++ code
4. Convert the float[][] to an IntPtr pointing to the address of the array
5. Convert the float[][] to a float* (requires unsafe code in C#)
6. Try combinations of the above, where you attempt a method signature in C++ using float[][], float[], float**, float*, and change the type you are sending from C# between IntPtr, float[], float*, float[][], float[,], float**, and in addition try mixing in the keywords out and ref as well
7. Do the same as you did in #6, but try copying the data to public memory using Marshal.Copy prior to making all the above calls

The above suggestions give you hundreds of combinations to try, and my guess is that at least one of them will work. Let us know if you get this figured out,

Sounds like somebody's got a case of the Mondays

-Jeff

Re: Passing dynamic 2 dim float array in c# to unmanaged c++ dll

f4hd11-Dec-07 9:34

regarding to dll hell with code

11-Dec-07 9:34

Hi Jeff

Thanks for your answers.

1. Change the C# import declaration type from float[,] to float[][] (they are NOT equivalent types A:I know Smile | :)

)
A: tried that before, gives a marshalling error.

2. Change the C++ method signiture to take parameters of type float[][] instead of float**
A: this doesnt work too, C++ gives lots of error if using flaot[][] instead of float**

3. Convert the float[][] to a float[] in your c# code, and change your method to either float* or float[] in your C++ code
A: I think this will work so if I got it right ill do the following:
float[,] --> float[] in c#
float* --> float** once in c++
float** --> float* when exiting from the function in c++
float[] --> float[][] in c#

it should work but isnt desireable.

4. Convert the float[][] to an IntPtr pointing to the address of the array
A:Can you help me with this please.

5. Convert the float[][] to a float* (requires unsafe code in C#)
A:Im not sure about this but perhaps dont want to try it right now.

6. Try combinations of the above, where you attempt a method signature in C++ using float[][], float[], float**, float*, and change the type you are sending from C# between IntPtr, float[], float*, float[][], float[,], float**, and in addition try mixing in the keywords out and ref as well

A Smile | :)

have tried many combinations already including Out and Ref but in all ive noticed that because memory isnt properly handled i can only access part of the 2d array accessing other parts causes access violation.

7. Do the same as you did in #6, but try copying the data to public memory using Marshal.Copy prior to making all the above calls
A: I dont know about this. Need to dig in to it.

I did read about pinning pointers and stuff but all that is for C++ not C#, if Im not mistaken 'ref' takes care of it, but i may be wrong.

>>The above suggestions give you hundreds of combinations to try, and my guess is that at least one >>of them will work. Let us know if you get this figured out,
A: sure ill let u all know Smile | :)

kind regards

creative2002guy11-Dec-07 2:57

creative2002guy

11-Dec-07 2:57

I want to know how the side by side versioning is maintain in dotnet.

1) if i used

<configuration>
<runtime>
<assemblybinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentassembly>
<assemblyidentity name="ClassLibraryversioning">
publicKeyToken="f690ee21283c8415"
culture="neutral"/>
<bindingredirect oldversion="1.0.0.0">
newVersion= "1.0.0.1"/>
</bindingredirect></assemblyidentity></dependentassembly>
</assemblybinding>
</runtime>
</configuration>

then it is always show same version(no compilation errors)

mean it always show the function in dll which i refered to the project.
even i specify bindingredirect

2) if i used following code then everthing is fine

{

Assembly objm = Assembly.Load("ClassLibraryversioning, Version=1.0.0.1,Culture=neutral, PublicKeyToken = f690ee21283c8415");
Type objmycom = objm.GetType("ClassLibraryversioning.Class1", true, true);
BindingFlags flags = (BindingFlags.NonPublic | BindingFlags.Public
| BindingFlags.Static | BindingFlags.Instance |
BindingFlags.DeclaredOnly);
MethodInfo m = objmycom.GetMethod("version", flags);
object myobj = Activator.CreateInstance(objmycom, false);
object result = m.Invoke(myobj, BindingFlags.InvokeMethod, null, null, CultureInfo.CurrentCulture);
MessageBox.Show(result.ToString());

}

tell me why it happened?

My problem is

Pete O'Hanlon11-Dec-07 3:17

Pete O'Hanlon

11-Dec-07 3:17

Tell you what. Pick one of these posts and stick with it then delete the others by using the Delete link at the bottom of the message.

Deja View - the feeling that you've seen this post before.

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Colin Angus Mackay11-Dec-07 3:22

Colin Angus Mackay

11-Dec-07 3:22

What about posting-to-forums hell?

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Luc Pattyn11-Dec-07 4:15

Luc Pattyn

11-Dec-07 4:15

This site badly needs message versioning and a difference tool.

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