Byte Array conversion question.

[mitsusdev]

Hi boys,
i'm newbie on B4A and you did a great job!!

Now, i've a question about byte array conversion and manipulation.
I read from bluetooth an Byte array of 60 bytes. So i want:

1. Change it (Byte Array) from Big Endian to Little Endian
2. Calculate integer value on 2 bytes, 4 bytes, ecc

I've seen many examples, but i'm not able to find a solution for my problem.

Thanks a lot

Francesco

 

[klaus]

Have a look at the ByteConverter library.

Best regards.

 

[mitsusdev]

Have a look at the ByteConverter library.

Best regards.

Hi Klaus,i've read about ByteConverter library. Below my test:

BConv.LittleEndian = True
BConv.ArrayCopy(Buffer, 0, header, 0,59) 
BConv.ArrayCopy(header,2,subHeader,0,4)
tmpInt = BConv.IntsFromBytes(subHeader) 
   
BConv.ArrayCopy(header,6,subHeaderDev,0,2)
tmpInt2 = BConv.IntsFromBytes(subHeaderDev)

strTmp = BConv.HexFromBytes(subHeaderDev)

I've a buffer (from bluetooth) of 74 bytes. The first 60 bytes are the header and the remaining 14 byes are the data.

I've divided global buffer into wo byte array using a Little Indiann rappresentation.
Now into tmpInt variable (an array of int) i want put 4 bytes from header and convert its into an integer of 4 bytes.

Using the code above, i see "tmpInt" with value 14 (correct!), but...tmpInt2 is not defined and strTmp have value (in Hex) 4101 insted of 1041.

Where are my errors?

Thanks a lot

 

[Erel]

I recommend you to write the buffer to a file:

   Dim out As OutputStream
   out = File.OpenOutput(File.DirRootExternal, "1.dat", False)
   out.WriteBytes(buffer, 0, buffer.length)
   out.Close

Then copy the file to the desktop and analyze it with a hex editor.

 

[mitsusdev]

I recommend you to write the buffer to a file:

   Dim out As OutputStream
   out = File.OpenOutput(File.DirRootExternal, "1.dat", False)
   out.WriteBytes(buffer, 0, buffer.length)
   out.Close

Then copy the file to the desktop and analyze it with a hex editor.

Thanks a lot Erel,
I try and update you tonight.

 

[mitsusdev]

I recommend you to write the buffer to a file:

   Dim out As OutputStream
   out = File.OpenOutput(File.DirRootExternal, "1.dat", False)
   out.WriteBytes(buffer, 0, buffer.length)
   out.Close

Then copy the file to the desktop and analyze it with a hex editor.

Dear Erel,
i've follow your advice. Now my question is that if i have a 2 byte array (Es. dc 07 in its hex conversion). I've tried to convert it into an ionteger using IntsFromBytes, but the output is wrong.
On my documentation i see that all integer fields are little-endian.

I've tried to use LittleEndian = True ...then I should see a new reversed string (07 dc)...but the result remains the same (dc 07).

Below the code:

BConv.ArrayCopy(header,9,arr_measure_data,0,2) 'Measure Year
BConv.LittleEndian = True
measure_data = BConv.HexFromBytes(arr_measure_data) 'I see DC07 insted of 07DC
Year = BConv.IntsFromBytes(arr_measure_data) ' should be 2012

Thanks a lot

 

[Erel]

Can you upload a small binary file with the data?

 

[mitsusdev]

Can you upload a small binary file with the data?

Hi Erel,
binary file uploaded: http://www.b4x.com/forum/attachment.php?attachmentid=11550&stc=1&d=1335270188

Thanks

 

[Erel]

Here is a solution with RandomAccessFile:

Sub Process_Globals
   Dim raf As RandomAccessFile
End Sub

Sub Globals

End Sub

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
      File.Copy(File.DirAssets, "1.txt", File.DirInternal, "1.txt")
      raf.Initialize2(File.DirInternal, "1.txt", False, True)
   End If
   Log(raf.ReadShort(9)) 'prints 2012
End Sub

 

[mitsusdev]

Here is a solution with RandomAccessFile:

Sub Process_Globals
   Dim raf As RandomAccessFile
End Sub

Sub Globals

End Sub

Sub Activity_Create(FirstTime As Boolean)
   If FirstTime Then
      File.Copy(File.DirAssets, "1.txt", File.DirInternal, "1.txt")
      raf.Initialize2(File.DirInternal, "1.txt", False, True)
   End If
   Log(raf.ReadShort(9)) 'prints 2012
End Sub

Dear Erel,
thank you for you help. I've solved follw your advise..so i store temporary data into a file and then i use raf.ReadBytes() for read a group of bytes.

Thanks a lot