Fileread null values

[Tsukihime]

This is my input text file "hello.txt" in hex:

00 00 68 65 6C 6C 6F

Which is basically "hello" with two null bytes before it.

I want to read 7 bytes starting from the beginning of the file then print out the results, so I would expect to get a couple null bytes and the word "hello"

I tried

$file = FileOpen("hello.txt", 1)
$line = FileRead($file, 7)
ConsoleWrite($line)

But nothing was printed out.

It seems like the null bytes cause problems. Why does that happen?

EDIT: ah, I left out a 6 in FileOpen...

lol

Ok so it is now in binary mode, but I still want to be able to see the word "hello" =/

Edited May 11, 2011 by Tsukihime

[kaotkbliss]

You probably have to convert back with BinaryToString?

[smartee]

hi Tsukihime,

Solution (Writing the ANSI representation of the file to the console):

#include <String.au3>

$file = @ScriptDir & "\NULL(2)hello.txt"

; Create casefile
If Not FileExists($file) Then
    $hnd = FileOpen($file, 17) ; Open for writing binary
    FileWrite($hnd, StringToBinary(_HexToString("000068656C6C6F")))
    FileClose($hnd)
EndIf

; Reading casefile
$hnd = FileOpen($file, 16) ; Open for reading binary
$bin = FileRead($hnd, FileGetSize($file))
For $i = 1 To BinaryLen($bin)
    ConsoleWrite(BinaryToString(BinaryMid($bin, $i, 1)))
Next
FileClose($hnd)

Explanation:

Strings, in AutoIt, are NULL-terminated character arrays, hence, whenever the NULL character is encountered the string is assumed to have ended.

See these examples:

#include <String.au3>

; NULLNULLhello but nothing is written
ConsoleWrite(_HexToString("000068656C6C6F"))

; helloNULLo but "hello" is written
ConsoleWrite(_HexToString("68656C6C6F006F"))

; Needless to say, you never see "important message"
ConsoleWrite(_HexToString("00") & "important message")

Hope this clears some things up

-smartee

[smartee]

hi,

PS: Some functions in AutoIt do read past the NULL characters when dealing with strings, making this a simple workaround:

#include <String.au3>

$file = @ScriptDir & "\NULL(2)hello.txt"

; Reading casefile
$hnd = FileOpen($file, 16) ; Open for reading binary
$bin = FileRead($hnd, FileGetSize($file))
ConsoleWrite(StringReplace(BinaryToString($bin), Chr(0), "")) ;Strip out NULL's and print
FileClose($hnd)

Regards,

-smartee

[kaotkbliss]

@smartee

I think you are too smart for your own good

[Tsukihime]

hi,

PS: Some functions in AutoIt do read past the NULL characters when dealing with strings, making this a simple workaround:

#include <String.au3>

$file = @ScriptDir & "\NULL(2)hello.txt"

; Reading casefile
$hnd = FileOpen($file, 16) ; Open for reading binary
$bin = FileRead($hnd, FileGetSize($file))
ConsoleWrite(StringReplace(BinaryToString($bin), Chr(0), "")) ;Strip out NULL's and print
FileClose($hnd)

Regards,

-smartee

Thanks, didn't think about replacing the null's. Edited May 11, 2011 by Tsukihime