The ReadChrAt$ function will read a string characters from any position within an open file channel. If the length parameter is set to zero, ratehr than the character length to read, then the command expects this string to be zero terminated.
FACTS:
* Reading none sequential pieces of data can be slow
* ReadChrAt$ only works with files opened with ReadFile
* ReadChrAt$ lets you randomly access any piece of data within the file.
Mini Tutorial:
This example creates a file and reads the with some various bits of data store in it, then read it's back again using the random access file commands.
; Create a file name
File$=TempDir$()+"PB_TestFile.txt"
; Get a Free File Channel Index
MyFile=GetFreeFile()
; CReate a File for writing data to
WriteFile File$,MyFile
; Write some Byte data at a byte pos 100
WriteByteAt 1,100,255
; Write some Word data at a byte pos 200
WriteWordAt 1,200,64000
; Write some Integer data at a byte pos 300
WriteIntAt 1,300,111222
; Write some Float data at a byte pos 400
WriteFloatAt 1,400,123.456
; Write some Stringt data at a byte pos 500
WriteStringAt 1,500,"Play Basic"
; Write some Stringt data at a byte pos 600
WriteChrAt 1,600,"Hello World",11
; Close this file channel
CloseFile MyFile
Print "============================"
Print "Reading File Data:"+File$
Print "============================"
; Get a Free File Channel Index
MyFile=GetFreeFile()
; Open a file to READ with READFILE
ReadFile File$,MyFile
; Read and display byte from position 100 in this file
Print ReadByteAt(myFile,100)
; Read and display the Word from position 200 in this file
Print ReadWordAt(myFile,200)
; Read and display the Integer from position 300 in this file
Print ReadIntAt(myFile,300)
; Read and display the Float from position 400 in this file
Print ReadFloatAt(myFile,400)
; Read and display the String from position 500 in this file
Print ReadStringAt$(myFile,500)
; Read and display the String from position 600 in this file
Print ReadChrAt$(myFile,600,11)
; Close this file channel
CloseFile MyFile
; Display the Size of the FIle
Print "============================"
Print "File Size:"+Str$(FileSize(file$))
Print "============================"
If FileExist(file$) Then DeleteFile file$
; Display the screen and wait for a key press
Sync
WaitKey
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This example would output.
============================
Reading File:C:Windows\temp\Pb_TestFile.txt
============================
255
64000
111222
123.456
Play Basic
Hello World
============================
File Size:611
============================
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