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Downgrade FromBase64String from vb.net to vb6

Posted on 2010-09-02
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Last Modified: 2012-05-10
      I have a .Net example application that uses FromBase64String which I need to convert one function from and place in my legacy VB6 application, but I have been unable to find equivenent code.  The function accepts strdata as a string, decodes it from base64 and saves it as a bmp file.  Can anyone tell me how to accomplish this in VB6????

This is the whole code of the function.
       
    Private Sub SaveImageData(ByVal sigdata As String)

        Dim b() As Byte = Convert.FromBase64String(strdata)
        Dim fs As IO.FileStream = IO.File.Create("C:\temp.bmp")
        fs.Write(b, 0, b.Length)
        fs.Close()

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Question by:FNDAdmin
4 Comments
 
LVL 17

Accepted Solution

by:
Zhaolai earned 2000 total points
ID: 33588024
The following link should be helpful:

http://www.nonhostile.com/howto-encode-decode-base64-vb6.asp

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LVL 12

Expert Comment

by:GMGenius
ID: 33588044
Here is a link to a sample class you could use
Use the DecodeToByteArray and save the byte array to file
http://www.mcmillan.org.nz/paradoxes/code/base64.html
I hope this helps
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LVL 29

Expert Comment

by:nffvrxqgrcfqvvc
ID: 33588276
You can also use the cryptography API

Option Explicit
'egl1044
'WinXP or later
Private Const CRYPT_STRING_BASE64 As Long = &H1&

Private Declare Function CryptStringToBinaryW Lib "Crypt32.dll" ( _
  ByVal pszString As Long, _
  ByVal cchString As Long, _
  ByVal dwFlags As Long, _
  ByVal pbBinary As Long, _
  ByRef pcbBinary As Long, _
  ByVal pdwSkip As Long, _
  ByVal pdwFlags As Long) As Long

Public Function FromBase64String(ByVal data As String) As Byte()
  Dim Buffer() As Byte
  Dim dwBinaryBytes As Long
  dwBinaryBytes = LenB(data)
  ReDim Buffer(dwBinaryBytes - 1) As Byte
  If CryptStringToBinaryW(StrPtr(data), LenB(data), CRYPT_STRING_BASE64, _
    VarPtr(Buffer(0)), dwBinaryBytes, 0, 0) Then
    ReDim Preserve Buffer(dwBinaryBytes - 1) As Byte
    FromBase64String = Buffer
  End If
  Erase Buffer
End Function

Private Sub Form_Load()
  Dim image() As Byte
  image() = FromBase64String("c3VyZS4=") 'sure.
  Debug.Print StrConv(image, vbUnicode)
End Sub

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Author Closing Comment

by:FNDAdmin
ID: 33596519
Thanks to everyone that posted solutions.  They all look like they shoudl work, but for some reason all three gave me a different decoded output, and only the XML was correct in my situation, I'm not exactly sure why.  Worked great though, thank you.
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