RE: Bug in My.Computer.FileSystem.WriteAllText
- From: wawang@xxxxxxxxxxxxxxxxxxxx ("Walter Wang [MSFT]")
- Date: Fri, 17 Aug 2007 06:34:03 GMT
Hi Bo,
The My.Computer.FileSystem.WriteAllText has two variations:
Public Sub WriteAllText( _
ByVal file As String, _
ByVal text As String, _
ByVal append As Boolean _
)
' -or-
Public Sub WriteAllText( _
ByVal file As String, _
ByVal text As String, _
ByVal append As Boolean, _
ByVal encoding As System.Text.Encoding _
)
The first one is using System.Text.Encoding.UTF8 as the default encoding.
The System.Text.Encoding.UTF8 is an instance of
System.Text.Encoding.UTF8Encoding.
The System.Text.Encoding.UTF8Encoding has a constructor which accepts a
boolean parameter named "encoderShouldEmitUTF8Identifier" (see
http://msdn2.microsoft.com/en-us/library/s064f8w2(VS.80).aspx): when it's
true (which is the case for the instance returned by
System.Text.Encoding.UTF8), it means that a Unicode byte order mark (short
for BOM) is provided.
Basically a BOM at the beginning of a file will help the applications that
are reading the file to determine what's the correct encoding of the file.
You may find more information about BOM here:
#Byte-order mark - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Byte_Order_Mark
#FAQ - UTF-8, UTF-16, UTF-32 & BOM
http://unicode.org/faq/utf_bom.html
#Byte Order Mark
http://msdn2.microsoft.com/en-us/library/ms776429.aspx
In .NET, when a encoding has specified BOM, the IO classes will output
those extra bytes in the beginning of a file when writing the file.
For notepad, it will try to detect the encoding from the BOM:
#The Old New Thing : Some files come up strange in Notepad
http://blogs.msdn.com/oldnewthing/archive/2004/03/24/95235.aspx
Hope this helps.
Sincerely,
Walter Wang (wawang@xxxxxxxxxxxxxxxxxxxx, remove 'online.')
Microsoft Online Community Support
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