用VB实现一个简单的ESMTP客户端

;   c4 = base64DecodeChars(c4)
            End If
        Loop While (i < len1 And c4 = -1)
        If (c4 = -1) Then
            base64decode = out
            Exit Function
        End If

        out = out + Chr(((c3 And 3) * 64) Or c4)
    Wend
    
    base64decode = out
End Function

Function utf16to8(str As String) As String


    Dim out, i, len1, c
    out = ""
    len1 = Len(str)
    For i = 1 To len1
        c = Asc(Mid(str, i, 1))
        If ((c >= 1) And (c <= 127)) Then
            out = out + Mid(str, i, 1)
        ElseIf (c > 2047) Then
            out = out + Chr(224 Or ((c \ 4096) And 15))
            out = out + Chr(128 Or ((c \ 64) And 63))
            out = out + Chr(128 Or (c And 63))
        Else
            out = out + Chr(192 Or ((c \ 64) And 31))
            out = out + Chr(128 Or (c And 63))
        End If
    Next
    utf16to8 = out
End Function

Function utf8to16(str As String) As String


    Dim out, i, len1, c
    Dim char2, char3

    out = ""
    len1 = Len(str)
    i = 0
    While (i < len1)
        c = Asc(Mid(str, i + 1, 1))
        i = i + 1
        Select Case (c \ 16)
    
        Case 0 To 7
            out = out + Mid(str, i, 1)
        
        Case 12, 13
            char2 = Asc(Mid(str, i + 1, 1))
            i = i + 1
            out = out