Random access files

Erel

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• Dec 29, 2010

• #2

You should use the RandomAccessFile library.
If you want to read strings you can read the bytes and then use BytesToString keyword to convert the bytes into string.

 

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D

Domingo

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• Dec 29, 2010

• #3

Yes, Ok.
Are there any example?

 

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Erel

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• Dec 30, 2010

• #4

What exactly are you trying to do?
To open a file you can use code similar to:

B4X:

Dim raf As RandomAccessFile
raf.Initialize(File.DirRootExternal, "1.dat", False)
Dim i As Int
i = raf.ReadInt(12) 'reads an integer stored in the 12 position.
Dim buffer(1024) As Byte
raf.ReadBytes(buffer, 0, 100, 1000) 'reads 100 bytes starting at position 1000
Dim s As String
s = BytesToString(buffer, 0, 100, "UTF-8") 'convert the bytes to string

 

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Domingo

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• Dec 30, 2010

• #5

Ok. This is that I tried it.
Thanks for all end happy new year

 

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Erel

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• Dec 30, 2010

• #6

Note that if you are working with text files then it will be easier to use File.ReadString or TextReader to read the text.

 

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Domingo

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• Dec 30, 2010

• #7

Yes, but I have a file created by random access file with basic4ppc and I want to work with it.
Thanks

 

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Domingo

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• Dec 31, 2010

• #8

Hi Erel
I tried the example that your post but do the next error:

Error compiling program.
Error description: Cannot cast type: {Type=Byte,Rank=0} to: {Type=Byte,Rank=1}
Occurred on line: 92
buffer = acceso.ReadBytes(buffer,0,100,1000)
Word: buffer

What is the problem?

 

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agraham

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• Dec 31, 2010

• #9

Domingo said:

buffer = acceso.ReadBytes(buffer,0,100,1000)

Click to expand...

It's an error by Erel. ReadBytes returns an integer count of bytes read and so cannot be assigned to an array variable. It should be something like

B4X:

Dim bytesread as Int
bytesread = acceso.ReadBytes(buffer,0,100,1000)

If I remember correctly ReadBytes doesn't guarantee to always return the numbert of bytes requested - but probably will in the case of a file. It might be wise to check the return value for the correct number of bytes.

 

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Erel

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• Dec 31, 2010

• #10

You are both right. I edited my previous post.

 

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rfresh

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• May 16, 2012

• #11

Can someone please show me how to get the file size using the .Size property with RAF's? Thank you...

Update: I got it!

B4X:

   If File.ExternalWritable = True Then
      'SD Card Installed
      pFilePath = File.DirRootExternal
   Else
      'No SD Card
      pFilePath = File.DirInternal
   End If
   raf.Initialize(pFilePath,pFilename,True)
   mFileSize = raf.Size

 

Last edited: May 16, 2012

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