❔ Problem with including C DLL in a C# console app project.

K

Kouhai•3/28/23, 8:54 PM

use dll viewer or dependency walker and check the exported symbols

A

acookookOP•3/28/23, 9:18 PM

It looks like it is a C++ function after all.
So what to include in the DLL import tag?

A

Accord•3/29/23, 9:24 PM

Looks like nothing has happened here. I will mark this as stale and this post will be archived until there is new activity.

KKouhai use dll viewer or dependency walker and check the exported symbols

A

acookookOP•4/1/23, 4:58 PM

Ok, I managed to get to work, but I am getting a

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'

System.AccessViolationException: 'Attempted to read or write protected memory. This is often an indication that other memory is corrupt.'

The function i tried to import is something along the lines

  //private static extern int calculateBP(ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

  //private static extern int calculateBP(ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(ushort[] data, uint len, char ch, uint samplingRate, IntPtr results); or

//private static extern int calculateBP(out ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(out ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(out ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(out ushort[] data, uint len, char ch, uint samplingRate, IntPtr results);

//private static extern int calculateBP(ref ushort[] data, uint len, char ch, uint samplingRate, ref Measurement[] results);

//private static extern int calculateBP(ref ushort[] data, uint len, char ch, uint samplingRate, ref Measurement[] results);

//private static extern int calculateBP(ref ushort[] data, uint len, char ch, uint samplingRate, ref Measurement[] results);

//private static extern int calculateBP(ref ushort[] data, uint len, char ch, uint samplingRate, ref Measurement[] results);

defined as

int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);
I triend numerous things, including to allocate some memmory using marshal, but still no luck. Any idea how to debug and solve this. The

measurement

measurement

measurement

measurement struct contains a number of

floats

floats

floats

floatsand

integers

integers

integers

integers which I have also defined, but apparently I can't call it correctly.

J

Jimmacle•4/1/23, 5:05 PM

it would help to see both the C++ function signature and struct definition and C# struct definition and marshalling code

J

Jimmacle•4/1/23, 5:05 PM

first thing i see is your data types are probably wrong and i don't believe

[DllImport]

[DllImport]

[DllImport]

[DllImport] automatically marshals arrays for you

A

acookookOP•4/1/23, 5:46 PM

The C++ function as defined in the header file is the following:

__declspec(dllexport) int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

__declspec(dllexport) int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

__declspec(dllexport) int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);

__declspec(dllexport) int CalculateBP(USHORT * data, UINT len, UCHAR ch, UINT samplingRate, measurement * results);
while the DLL import is the following:

[DllImport("BPCalculationDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "?CalculateBP@@YAHPAGIEIPAUmeasurement@@@Z")]

[DllImport("BPCalculationDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "?CalculateBP@@YAHPAGIEIPAUmeasurement@@@Z")]

[DllImport("BPCalculationDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "?CalculateBP@@YAHPAGIEIPAUmeasurement@@@Z")]

[DllImport("BPCalculationDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "?CalculateBP@@YAHPAGIEIPAUmeasurement@@@Z")]

The C is defined by

typedef struct{
    float val1;
    float val2;
    int numBettween;
    int error;
} measurement;

typedef struct{
    float val1;
    float val2;
    int numBettween;
    int error;
} measurement;

typedef struct{
    float val1;
    float val2;
    int numBettween;
    int error;
} measurement;

typedef struct{
    float val1;
    float val2;
    int numBettween;
    int error;
} measurement;

I meant by marshaling is that is tried to use methods to deal with unmanaged code (from the

System.Runtime.InteropServices.Marshal

System.Runtime.InteropServices.Marshal

System.Runtime.InteropServices.Marshal

System.Runtime.InteropServices.Marshal namespace), but to no success. I also trie some combinations mentioned on SO (https://stackoverflow.com/questions/28595903/copy-from-intptr-16-bit-array-to-managed-ushort), but no success.

Stack Overflow

Copy from IntPtr (16 bit) array to managed ushort

I have a IntPtr called rawbits, which points to a 10MB array of data, 16 bit values. I need to return a managed ushort array from that. The following code works but there is an extra BlockCopy I wo...

J

Jimmacle•4/1/23, 5:48 PM

not just the dllimport attribute, the whole method signature

A

acookookOP•4/1/23, 5:50 PM

so as I defined it in C#?

J

Jimmacle•4/1/23, 5:50 PM

right

A

acookookOP•4/1/23, 5:51 PM

J

Jimmacle•4/1/23, 5:51 PM

first thing is C++ chars aren't the same as C# chars, the former is 1 byte and the second is 2 bytes

A

acookookOP•4/1/23, 5:51 PM

I tried multiple approaches with multiple combinations, but none of the seem to give the desired result

J

Jimmacle•4/1/23, 5:51 PM

second you can't pass arrays to unmanaged code like that, the GC could move them while the unmanaged code is trying to work with them and that would be Bad

J

Jimmacle•4/1/23, 5:51 PM

they have to be pinned

J

Jimmacle•4/1/23, 5:52 PM

if you use the new-ish

LibraryImport

LibraryImport

LibraryImport

LibraryImport attribute instead of

DllImport

DllImport

DllImport

DllImport it can generate that code for you

A

acookookOP•4/1/23, 5:53 PM

oh, I understand

JJimmacle if you use the new-ish `LibraryImport` attribute instead of `DllImport` it can g...

A

acookookOP•4/1/23, 5:54 PM

How exactly do I do that?

J

Jimmacle•4/1/23, 5:55 PM

it's more or less just replacing the attribute

J

Jimmacle•4/1/23, 5:55 PM

https://learn.microsoft.com/en-us/dotnet/standard/native-interop/pinvoke-source-generation

P/Invoke source generation

Learn about compile-time source generation for platform invokes in .NET.

A

acookookOP•4/1/23, 5:55 PM

oh, nevermind

A

acookookOP•4/1/23, 5:56 PM

is this something in .net 7 only?

J

Jimmacle•4/1/23, 5:56 PM

yeah

A

acookookOP•4/1/23, 5:56 PM

ok

A

acookookOP•4/1/23, 5:56 PM

then I need first to upgrade to .net 7 from 5

J

Jimmacle•4/1/23, 5:56 PM

if you can you might as well

J

Jimmacle•4/1/23, 5:57 PM

if not you can hand-write the same code that

LibraryImport

LibraryImport

LibraryImport

LibraryImport would generate

A

acookookOP•4/1/23, 6:03 PM

ok, so now i have this

A

acookookOP•4/1/23, 6:03 PM

A

acookookOP•4/1/23, 6:03 PM

an 3 errors

K

Kouhai•4/1/23, 6:12 PM

You need to specify which parameter is used for the array's size @šanji

A

acookookOP•4/1/23, 6:12 PM

like that?

A

acookookOP•4/1/23, 6:13 PM

[MarshalAs(unmanagedType: UnmanagedType.LPArray)] ushort[] data

[MarshalAs(unmanagedType: UnmanagedType.LPArray)] ushort[] data

[MarshalAs(unmanagedType: UnmanagedType.LPArray)] ushort[] data

[MarshalAs(unmanagedType: UnmanagedType.LPArray)] ushort[] data

K

Kouhai•4/1/23, 6:15 PM

No like,

[MarshalAs(SizeParamIndex=1)] ushort[] data

[MarshalAs(SizeParamIndex=1)] ushort[] data

[MarshalAs(SizeParamIndex=1)] ushort[] data

[MarshalAs(SizeParamIndex=1)] ushort[] data
iirc default marshaling for arrays is already LPArray,

A

acookookOP•4/1/23, 6:16 PM

ok, so i am actuall more lost that I was before

K

Kouhai•4/1/23, 6:17 PM

Okay, SizeParamIndex just specifies that the parameter index we'll use to indicate the length of the array data is at position

1

K

Kouhai•4/1/23, 6:18 PM

which is uint len

A

acookookOP•4/1/23, 6:21 PM

this just gives me an error

K

Kouhai•4/1/23, 6:23 PM

oops sorry

[MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)]

[MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)]

[MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)]

[MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)]

A

acookookOP•4/1/23, 6:24 PM

no problem

A

acookookOP•4/1/23, 6:45 PM

So i just need to figure out this

A

acookookOP•4/1/23, 6:48 PM

nevermin, it's a byte

A

acookookOP•4/1/23, 6:52 PM

ok...I think I got it.

 private static partial int calculateBP([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] ushort[] data, uint len, [MarshalAs(UnmanagedType.U1)] byte ch, uint samplingRate, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] Measurement[] results);

 private static partial int calculateBP([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] ushort[] data, uint len, [MarshalAs(UnmanagedType.U1)] byte ch, uint samplingRate, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] Measurement[] results);

 private static partial int calculateBP([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] ushort[] data, uint len, [MarshalAs(UnmanagedType.U1)] byte ch, uint samplingRate, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] Measurement[] results);

 private static partial int calculateBP([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] ushort[] data, uint len, [MarshalAs(UnmanagedType.U1)] byte ch, uint samplingRate, [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] Measurement[] results);

So now just need to pass in the neccessarry data and any empty measurement array of structs and I am golden? Do I need to worry if that the data is processed by other functions of the DLL and then that data can be corrupt?

A

acookookOP•4/1/23, 7:19 PM

Ok, I definitely need to think deeper, since I get invalid measurement results out of the function, and also other functions return invalid data.

Aacookook Ok, I definitely need to think deeper, since I get invalid measurement results o...

K

Kouhai•4/1/23, 7:57 PM

Can you show your C++ definition?

K

Kouhai•4/1/23, 7:57 PM

I guess you've already sent it

K

Kouhai•4/1/23, 7:58 PM

I think you're misunderstanding what passing an array by ref means

K

Kouhai•4/1/23, 7:58 PM

passing an array by ref is basically passing a pointer to the array

K

Kouhai•4/1/23, 7:59 PM

ref int[]

ref int[]

ref int[]

ref int[] is the equivalent of

int**

int**

int**

int** in C/C++

A

acookookOP•4/1/23, 8:46 PM

yeah I just would like to finally solve this issue. Although I fixed the DLL importing issue, I probably just too plug in different numbers