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Decode and Encode UTF-8

Article by:

Hans Kalle (9/2/2006)

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Summary:

When reading and writing xml-files like rss-feeds, one needs to convert data from the Windows character set to UTF-8. This script is all you need.

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Decode and Encode UTF-8

All encoding and decoding is done by the functions in the utf8.asp file:

Select All Code

<%
option explicit 

' Simple functions to convert the first 256 characters 
' of the Windows character set from and to UTF-8.

' Written by Hans Kalle for Fisz
' http://www.fisz.nl

'IsValidUTF8
'  Tells if the string is valid UTF-8 encoded
'Returns:
'  true (valid UTF-8)
'  false (invalid UTF-8 or not UTF-8 encoded string)
function IsValidUTF8(s)
  dim i
  dim c
  dim n

  IsValidUTF8 = false
  i = 1
  do while i <= len(s)
    c = asc(mid(s,i,1))
    if c and &H80 then
      n = 1
      do while i + n < len(s)
        if (asc(mid(s,i+n,1)) and &HC0) <> &H80 then
          exit do
        end if
        n = n + 1
      loop
      select case n
      case 1
        exit function
      case 2
        if (c and &HE0) <> &HC0 then
          exit function
        end if
      case 3
        if (c and &HF0) <> &HE0 then
          exit function
        end if
      case 4
        if (c and &HF8) <> &HF0 then
          exit function
        end if
      case else
        exit function
      end select
      i = i + n
    else
      i = i + 1
    end if
  loop
  IsValidUTF8 = true 
end function

'DecodeUTF8
'  Decodes a UTF-8 string to the Windows character set
'  Non-convertable characters are replace by an upside
'  down question mark.
'Returns:
'  A Windows string
function DecodeUTF8(s)
  dim i
  dim c
  dim n

  i = 1
  do while i <= len(s)
    c = asc(mid(s,i,1))
    if c and &H80 then
      n = 1
      do while i + n < len(s)
        if (asc(mid(s,i+n,1)) and &HC0) <> &H80 then
          exit do
        end if
        n = n + 1
      loop
      if n = 2 and ((c and &HE0) = &HC0) then
        c = asc(mid(s,i+1,1)) + &H40 * (c and &H01)
      else
        c = 191 
      end if
      s = left(s,i-1) + chr(c) + mid(s,i+n)
    end if
    i = i + 1
  loop
  DecodeUTF8 = s 
end function

'EncodeUTF8
'  Encodes a Windows string in UTF-8
'Returns:
'  A UTF-8 encoded string
function EncodeUTF8(s)
  dim i
  dim c

  i = 1
  do while i <= len(s)
    c = asc(mid(s,i,1))
    if c >= &H80 then
      s = left(s,i-1) + chr(&HC2 + ((c and &H40) / &H40)) + chr(c and &HBF) + mid(s,i+1)
      i = i + 1
    end if
    i = i + 1
  loop
  EncodeUTF8 = s 
end function
%>

To test the functions, one can use the code below. Place this code in a separate file, utf8test.asp for example.

Select All Code

<!--#include file="utf8.asp"-->
<html>
<head>
<title>Test UTF encoding en decoding</title>
<head/>
<body>
<h1>Decoding</h1>
<p>Kopiëren ok: <%=DecodeUTF8("KopiÅ«ren")%></p>
<p>Kopiëren error: <%=DecodeUTF8("Kopiëren")%></p>
<p>Kopiëren error: <%=DecodeUTF8("KopiÅren")%></p>
<p>Kopiëren error: <%=DecodeUTF8("KopiÅ««ren")%></p>
<p>Kopiëren error: <%=DecodeUTF8("Kopià«ren")%></p>
<h1>Encoding</h1>
<p>Kopiëren UTF-8: <%=EncodeUTF8("Kopiëren")%></p>
<p>Kopiëren forth & back: <%=DecodeUTF8(EncodeUTF8("Kopiëren"))%></p>
<h1>Testing encoding</h1>
<p>Kopiëren: <%=IsValidUTF8("Kopiëren")%></p> 
<p>KopiÅ«ren: <%=IsValidUTF8("KopiÅ«ren")%></p> 
<p>KopiÅ««ren: <%=IsValidUTF8("KopiÅ««ren")%></p> 
<p>Aeroplane: <%=IsValidUTF8("Aeroplane")%></p> 
</body>
</html>

Good luck and have fun!

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User Comments on 'Decode and Encode UTF-8'

Posted by : sinan at 12:14 on Saturday, December 08, 2007

thank you

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