(Visual Basic 6.0) Append Text Data to an Existing ZIP Entry Using ZipEntry.AppendString

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This example demonstrates how to use the ZipEntry.AppendString method to append text data to an existing ZIP entry.

The example opens an existing ZIP archive, locates a text file entry, and appends additional text to the end of the file contents.

An important concept demonstrated by this example is that appending data to a ZIP entry transforms the entry into an in-memory Data Entry (EntryType = 2).

For example:

• If the entry is a mapped entry from an opened ZIP archive (EntryType = 0), the compressed entry is first inflated into memory.
• If the entry is a referenced filesystem file (EntryType = 1), the file contents are first loaded into memory.

The new text is then appended to the uncompressed in-memory data, and the entry becomes a Data Entry.

After the ZIP archive is rewritten, the modified entry again becomes a mapped entry stored within the ZIP archive.

Note: This example requires Chilkat v11.0.0 or greater.

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Dim success As Long
success = 0

Dim zip As New ChilkatZip

' ------------------------------------------------------------
' Open an existing ZIP archive.
success = zip.OpenZip("c:/temp/notes.zip")
If (success = 0) Then
    Debug.Print zip.LastErrorText
    Exit Sub
End If

' Locate a text file entry within the ZIP archive.
Dim entry As New ChilkatZipEntry

success = zip.EntryOf("notes/readme.txt",entry)

If (success <> 0) Then

    ' --------------------------------------------------------
    ' At this point, the entry is a mapped entry because it
    ' originates from an opened ZIP archive.
    ' 
    '     EntryType = 0
    ' 
    Debug.Print "Initial EntryType = " & entry.EntryType

    ' Append additional text to the ZIP entry.
    ' 
    ' The existing compressed ZIP entry is first inflated
    ' into memory. The new text is then appended.
    ' 
    ' After AppendString is called, the entry becomes
    ' an in-memory Data Entry:
    ' 
    '     EntryType = 2
    ' 
    success = entry.AppendString(vbCrLf & "Additional notes added later.","utf-8")

    If (success = 0) Then
        Debug.Print zip.LastErrorText
        Exit Sub
    End If

    Debug.Print "EntryType after AppendString = " & entry.EntryType

    ' --------------------------------------------------------
    ' Write the modified ZIP archive to a different file.
    ' 
    ' Changing zip.FileName causes the ZIP archive to be
    ' written to a new output file rather than overwriting
    ' the original ZIP archive.
    ' 
    zip.FileName = "qa_output/updatedExample.zip"

    ' Rewrite the ZIP archive.
    ' 
    ' The modified in-memory entry is compressed and written
    ' into the new ZIP archive.
    ' 
    success = zip.WriteZip()
    If (success = 0) Then
        Debug.Print zip.LastErrorText
        Exit Sub
    End If

    ' After rewriting the ZIP archive, the entry again becomes
    ' a mapped entry:
    ' 
    '     EntryType = 0
    ' 
    Debug.Print "EntryType after WriteZip = " & entry.EntryType
End If

zip.CloseZip 

Debug.Print "ZIP entry updated successfully."