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<h1>FilePos (filehandle)</h1>
<h1>Parameters</h1>
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<td>
filehandle = the variable returned by the Readfile WriteFile or OpenFile  when the file was opened. The value returned is the offset from the start of  the file. ( 0 = Start of the file )
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<h1>Description</h1>
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This command returns the current position within a file that is being processed  following ReadFile, WriteFile or OpenFile. The returned integer is the offsets  in bytes from the start of the file to the current read/write position. Note,  this is zero when pointing to the first byte of the file.

<br />

<br />
By using FilePos and SeekFile the position within the file that is being read  or written can be determined and also changed. This allows a file to be read  and updated without having to make a new copy of the file or working through  the whole file sequentially. This could be useful if you have created a database  file and you want to find and update just a few records within it. It is also  possible to create an index file that contains pointers to where each record  starts in a data file.
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<h1><a href=../2d_examples/FilePos.bb>Example</a></h1>
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; Changing part of a file using OpenFile, SeekFile, FilePos
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; note FilePos is used in the SearchFile function at the end of this example
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<br />
; Open/create a file to Write
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fileout = WriteFile("mydata.dat")
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; Write the information to the file
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WriteInt( fileout, 1 )
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WriteInt( fileout, 2 )
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WriteInt( fileout, 3 )
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WriteInt( fileout, 4 )
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WriteInt( fileout, 5 )
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; Close the file
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CloseFile( fileout )
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DisplayFile( "The file as originally written", mydata.dat" )
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Position = SearchFile( 4 , "mydata.dat" )
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Write "Value 4 was found "
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Write Position
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Print " bytes from the start."
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Print
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<br />
; Open the file and change the value 3 to 9999
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file = OpenFile("mydata.dat")
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SeekFile( file, Position ) ; Move to the found location
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WriteInt( file, 9999 ) ; Replace the original value with 9999
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CloseFile( file )
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DisplayFile( "The file after being modified", "mydata.dat" )
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WaitKey()
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End ; End of program
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<br />
; **** Function Definitions follow ****
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; Read the file and print it
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Function DisplayFile( Tittle$, Filename$ )
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Print tittle$
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file = ReadFile( Filename$ )
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While Not Eof( file )
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Number = ReadInt( file )
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Print Number
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Wend
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CloseFile( file )
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Print
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End Function
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; Search a file of integers for the Wanted data value
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; Note the need to subtract 4 from the location since having read it
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; we are now pointing at the next Integer also Return() was placed
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; after closing the file so it is closed properly
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Function SearchFile( Wanted, Filename$ )
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file = ReadFile( Filename$ )
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While Not Eof( file )
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If ReadInt( file ) = Wanted Then Location = FilePos( file ) - 4
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Wend
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CloseFile( file )
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Return( Location )
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End Function
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