DllImport("msvcrt.dll") not working when it runs on linux

Question

I want to compare 2 bytes array using memcmp function using below code

[DllImport("msvcrt.dll",EntryPoint = "memcmp", CallingConvention = CallingConvention.Cdecl)]
  static extern int memcmp(byte[] b1, byte[] b2, long count);

When I run my application on Windows it is working fine. But when I run it on Linux it giving below exception

Unable to load shared library 'msvcrt.dll' or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: libmsvcrt.dll: cannot open shared object file: No such file or directory

Below is the docker file

FROM microsoft/dotnet:2.2-sdk AS build-env
WORKDIR /app

COPY *.csproj ./
COPY NuGet.Config ./
RUN dotnet restore

# copy everything else and build
COPY . ./

RUN dotnet publish -c Release -o out

# build runtime image
FROM microsoft/dotnet:2.2-runtime

WORKDIR /app
COPY --from=build-env /app/out .

ENTRYPOINT ["dotnet", "XXX.dll", "YYY.dll"]

Please let me know what should I use?

With all due respect, calling out to an external dll from a .net app in order to compare two byte arrays seems somewhat silly. — 500 - Internal Server Error, Sep 20 '19 at 08:09
Looks like it really wants to be [`Span.SequenceCompareTo`](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.sequencecompareto?view=netstandard-2.1#System_MemoryExtensions_SequenceCompareTo__1_System_Span___0__System_ReadOnlySpan___0__) — Damien_The_Unbeliever, Sep 20 '19 at 08:16
That name starting with "ms" is suspicious, looks like a Microsoft DLL so it is platform specific (windows only). — Cleptus, Sep 20 '19 at 08:16
@500-InternalServerError Tell that to the npm-community/javascript-'developers' — Rick, Sep 20 '19 at 08:17
_"for performance i need to use this function."_ - No, you don't. — Fildor, Sep 20 '19 at 08:56
@Damien_The_Unbeliever. Thanks. It works. Performance is same like memcmp. — vaishali khatri, Sep 20 '19 at 10:40

score 2 · Answer 1 · answered Sep 20 '19 at 08:13

2

You cannot just use a 'windows' DLL on Linux. Just because you have a .NET Core runtime on Linux doesn't mean you can use other libraries / executables from the other platform/OS.

You should find some other code that can compare two byte arrays or stick to windows as the underlying OS.

Take a look here: Comparing two byte arrays in .NET

answered Sep 20 '19 at 08:13

Rick

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I have used foor loop, sequence equal, structural equal and finally i choose memcmp which gives good performance as compared to all. Could someone tell how I can i use equivalent dll for linux. I think libc.so can be use but dont know how to implement it in code. Is it some thing to add in docker file? – vaishali khatri Sep 20 '19 at 08:33
@vaishalikhatri With the knowledge gained, I'd say you could compose a new SO question when stuck. – Rick Sep 20 '19 at 08:36
You can PInvoke the libc.so library. Check https://stackoverflow.com/a/42118816/2265446 – Cleptus Sep 20 '19 at 10:53

score 0 · Accepted Answer · answered Sep 20 '19 at 10:43

0

@Damien_The_Unbeliever. Thanks for your help. I used below code

 if (((ReadOnlySpan<byte>)slice).SequenceCompareTo((ReadOnlySpan<byte>)masterSlice) == 0)
                    isEqual = true;

answered Sep 20 '19 at 10:43

vaishali khatri

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DllImport("msvcrt.dll") not working when it runs on linux

2 Answers2