C#•2y ago

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

So I have this C DLL imported into my console app (.NET 5). I simply cannot get to call it correctly, since everytime I get, something along the lines, that something with the entrypoint is broken, like:

System.EntryPointNotFoundException: 'Unable to find an entry point named 'getCalculatedFitting' in DLL 'BPCalculationDLL.dll'.'

The code with which I am defining this is

[DllImport("BPCalculationDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "getCalculatedFitting")]
        public static extern int getCalculatedFitting(float[] fittinglData, uint length, char ch);

Honestly I tried a few things, but none of them seem to work in the current VS2022 editor. Does anyone have any idea how import this DLL and call it in another function?

60 Replies

Kouhai•2y ago

use dll viewer or dependency walker and check the exported symbols

acookookOP•2y ago

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

Accord•2y ago

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

acookookOP•2y ago

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.'

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); or //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);

defined as 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 struct contains a number of floatsand integers which I have also defined, but apparently I can't call it correctly.

Jimmacle•2y ago

it would help to see both the C++ function signature and struct definition and C# struct definition and marshalling code first thing i see is your data types are probably wrong and i don't believe [DllImport] automatically marshals arrays for you

acookookOP•2y ago

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); while the DLL import is the following:

[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;

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

Jimmacle•2y ago

not just the dllimport attribute, the whole method signature

acookookOP•2y ago

so as I defined it in C#?

Jimmacle•2y ago

right

acookookOP•2y ago

Jimmacle•2y ago

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

acookookOP•2y ago

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

Jimmacle•2y ago

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 they have to be pinned if you use the new-ish LibraryImport attribute instead of DllImport it can generate that code for you

acookookOP•2y ago

oh, I understand How exactly do I do that?

Jimmacle•2y ago

it's more or less just replacing the attribute

Jimmacle•2y ago

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.

acookookOP•2y ago

oh, nevermind is this something in .net 7 only?

Jimmacle•2y ago

yeah

acookookOP•2y ago

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

Jimmacle•2y ago

if you can you might as well if not you can hand-write the same code that LibraryImport would generate

acookookOP•2y ago

ok, so now i have this

acookookOP•2y ago

an 3 errors

Kouhai•2y ago

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

acookookOP•2y ago

like that?

acookookOP•2y ago

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

Kouhai•2y ago

No like, [MarshalAs(SizeParamIndex=1)] ushort[] data iirc default marshaling for arrays is already LPArray,

acookookOP•2y ago

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

Kouhai•2y ago

😅 Okay, SizeParamIndex just specifies that the parameter index we'll use to indicate the length of the array data is at position 1 which is uint len

acookookOP•2y ago

this just gives me an error

Kouhai•2y ago

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

acookookOP•2y ago

no problem

acookookOP•2y ago

So i just need to figure out this

acookookOP•2y ago

nevermin, it's a byte 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);

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

Kouhai•2y ago

Can you show your C++ definition? I guess you've already sent it I think you're misunderstanding what passing an array by ref means passing an array by ref is basically passing a pointer to the array ref int[] is the equivalent of int** in C/C++

acookookOP•2y ago

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

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

acookookOP•2y ago

Ok, so it seems that I magnaged VS no to crash on the call of the function, but something just doesn't seem right since i don't get the expected values in other functions

Kouhai•2y ago

Hmmm, Are you still passing ref arrays?

acookookOP•2y ago

getCalculatedFittingSize(UCHAR ch) is always returning zero, but anything above should be the result. The c# call is th following. private static partial int getCalculatedFittingSize([MarshalAs(UnmanagedType.U1)] byte cuffNumber); so now I am having the the function defined as

 private static partial int CalculateBP([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] ushort[] data, uint len, [MarshalAs(UnmanagedType.U1)] byte cuffNumber, uint samplingRate, ref Measurement result);

and calling it as CalculateBP(dataToUShort, (uint)dataToUShort.Length, 0, samplingRate, ref result);

Kouhai•2y ago

Okay, first are you 100% sure the C++ method produces the correct results?

acookookOP•2y ago

yes, the same underlying code is used else where, so i am sure it is my C# code, not the C++ code.

Kouhai•2y ago

Can you show your Measurement struct? Both C# and C++

acookookOP•2y ago

the c++ struct is here https://discord.com/channels/143867839282020352/1090377331970949250/1091780654854840512 and C# stuct is

[StructLayout(LayoutKind.Sequential)]
public struct Measurement
{
    [MarshalAs(UnmanagedType.R4)]
    float sys;

    [MarshalAs(UnmanagedType.R4)]
    float dia;

    [MarshalAs(UnmanagedType.R4)]
    float max;

    [MarshalAs(UnmanagedType.R4)]
    float amp;

    [MarshalAs(UnmanagedType.R4)]
    float hr;

    [MarshalAs(UnmanagedType.I4)]
    int maxIdx;

    [MarshalAs(UnmanagedType.I4)]
    int err;
}

Kouhai•2y ago

which fields have wrong values?

acookookOP•2y ago

based on the c++ logic (which is not documented I can't say for sure, but since the int err is always zero, the values do not break the code or result in an error

Kouhai•2y ago

Unfortunately that's not how it'll work Because your struct is different from this

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

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

This struct's error is at offset 0xC Meanwhile your 0xC offset is for amp The offsets are basically like this

typedef struct{
    float val1; // 0x0
    float val2; // 0x4
    int numBettween; // 0x8
    int error; // 0xC
} measurement

typedef struct{
    float val1; // 0x0
    float val2; // 0x4
    int numBettween; // 0x8
    int error; // 0xC
} measurement

public struct Measurement
{
    [MarshalAs(UnmanagedType.R4)]
    float sys; // 0x0

    [MarshalAs(UnmanagedType.R4)]
    float dia; // 0x4

    [MarshalAs(UnmanagedType.R4)]
    float max; // 0x8

    [MarshalAs(UnmanagedType.R4)]
    float amp; // 0xC

    [MarshalAs(UnmanagedType.R4)]
    float hr; // 0x10

    [MarshalAs(UnmanagedType.I4)]
    int maxIdx; // 0x14

    [MarshalAs(UnmanagedType.I4)]
    int err; // 0x18
}

public struct Measurement
{
    [MarshalAs(UnmanagedType.R4)]
    float sys; // 0x0

    [MarshalAs(UnmanagedType.R4)]
    float dia; // 0x4

    [MarshalAs(UnmanagedType.R4)]
    float max; // 0x8

    [MarshalAs(UnmanagedType.R4)]
    float amp; // 0xC

    [MarshalAs(UnmanagedType.R4)]
    float hr; // 0x10

    [MarshalAs(UnmanagedType.I4)]
    int maxIdx; // 0x14

    [MarshalAs(UnmanagedType.I4)]
    int err; // 0x18
}

acookookOP•2y ago

yeah, my mistake...I was truncationg it,just to write minimum code the C# fields are present in C++ also

Kouhai•2y ago

Huh, so CalculateBP should run okay then

acookookOP•2y ago

so basically my values are messed up?

Kouhai•2y ago

I honestly don't see what could fail, if you have the access to the source code you could step into it and see what happens after marshaling

acookookOP•2y ago

is there a way to debug this DLL code? I mean like calling it from C#

Kouhai•2y ago

Assuming you're using visual studio you just have to enable this on your launch profile

Kouhai•2y ago

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

acookookOP•2y ago

Ok, so managed to get it to work, but after a few files have been successfully processed, I just a NullReferenceException and an Unable ro read memory in the "Watch" tab for the needed array. My guess is that i ran out of addressable memory. How to overcome that?

Kouhai•2y ago

Why are you assuming you're running out of addressable memory? 😅

acookookOP•2y ago

Because I can easily process a few files without any issues First I thought a file was corrupt, but then I tried out a new, independent set of files Apparently it is the last file that is being processed and the last data structure in this file.

Unknown User•2y ago

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Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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