Cannot read string value written by MDFWriter

[Simplxss]

TestWriter()
{
    var Writer = new MdfWriter(MdfWriterType.Mdf4Basic);
    Writer.Init(TestFile4);
    var dg = Writer.CreateDataGroup();
    var cg = dg.CreateChannelGroup();
    var cn = cg.CreateChannel();
    cn.Name = "String";
    cn.Description = "string";
    cn.Type = ChannelType.FixedLength;
    cn.DataType = ChannelDataType.StringAscii;
    cn.DataBytes = 10;
    Writer.InitMeasurement();
    Writer.StartMeasurement((ulong)(DateTimeOffset.Now.ToUnixTimeMilliseconds() * 1000000));

    // i from 0 to 49
    cn.SetChannelValue(i.ToString());

    Writer.StopMeasurement((ulong)(DateTimeOffset.Now.ToUnixTimeMilliseconds() * 1000000));
    Writer.FinalizeMeasurement();
}
TestReader2()
{
    var Reader = new MdfReader(TestFile4);
    Reader.ReadEverythingButData();
    // ... create channel observer
    Reader.ReadData(group);
    string channel_value = ""; // Channel value (no scaling)
    string eng_value = ""; // Engineering value
    (MdfChannelObserver)item.GetChannelValueAsString(i, ref channel_value);
    (MdfChannelObserver)item.GetEngValueAsString(i, ref eng_value);
    Console.WriteLine($"channel_value = {channel_value}, eng_value= {eng_value}");
}

Detail code see TestWriter & TestReader2 functions in google test.

I viewed the output file and found the string seems writting correctly(?).

But all values in value_list_ of ChannelObserver are "" when reading. It seems that there are some problems in Reader.ReadData(). I have tried to solve it, but It's a little diffcult for me to fully understand how it works...

[ihedvall]

In general, you shouldn't use fixed length string. MDF file format and strings, doesn't go well together.

If you change the string channels data type to a variable length type and set data size to 4 or 8 bytes (this is the index size). See also unit test TestWrite::StringData.

However fixed length strings should work. I do a unit test for this and check what's the problem is.

[ihedvall]

I think the problem is solved. It was working for the first channel but not for the next channels. You can verify in .NET world.

[Simplxss]

It works well now, but I'm confused that why it needs to convent ASCII to UTF-8 encoding. In my view that UTF-8 contains ASCII tables.

---

From: Ingemar Hedvall @.> Sent: Wednesday, July 26, 2023 3:46 PM To: ihedvall/mdflib @.> Cc: Simplxs @.>; Author @.> Subject: Re: [ihedvall/mdflib] Cannot read string value written by MDFWriter (Issue #26)

I think the problem is solved. It was working for the first channel but not for the next channels. You can verify in .NET world.

— Reply to this email directly, view it on GitHubhttps://github.com/ihedvall/mdflib/issues/26#issuecomment-1651159022, or unsubscribehttps://github.com/notifications/unsubscribe-auth/AKUBLRDRSHUYJ44IXAAUHF3XSDDNLANCNFSM6AAAAAA2X3WJZU. You are receiving this because you authored the thread.Message ID: @.***>

[ihedvall]

I think ASCII also include the 0x10-0xFF characters. I'm using UTF8 if possible.

I have a question regarding timestamp value. C++ is still missing a timestamp value but when using Protobuf/gRPC. I'm using a protobuf version. Do C#/.NET have a standard way of expressing an absolute time which is better than using the nano-second definition from C++?

[Simplxss]

Sorry, in fact I'm not familiar with C#/.NET. But I don't think there is an appropriate way to process time better than timestamp. DateTime in C# could only handle 1/10 000 ms at most.

[ihedvall]

It is coming in .NET 7(+?)

[Simplxss]

Yes, DateTime will be impoved in .NET 7, but we can't trial it before .NET 8 releasing...