Introduction

• The operations described in this article report progress using callback objects. For more information about using callback objects, see Progress Notifications: Using Callback Objects.
• To read about preventing archive corruption in some cases, see Compressing Data.

Replacing

• To replace an existing file in an archive with a new file, use the CZipArchive::AddNewFile(CZipAddNewFileInfo&) method and specify the index of the file to be replaced in CZipAddNewFileInfo::m_uReplaceIndex.
• The operation replaces the file physically and no information from the file being replaced is retained (such as attributes, modification time, encryption method, etc.).
• If CZipAddNewFileInfo::m_iComprLevel is not 0 then a file to be added is first compressed to a temporary archive which is created in:
  • the temporary directory (see the CZipArchive::SetTempPath() method)
  • or in the memory, if you specify CZipArchive::zipsmMemoryFlag in CZipAddNewFileInfo::m_iSmartLevel.

    CZipArchive zip;
    zip.Open(_T("C:\\Temp\\test.zip"));
    CZipAddNewFileInfo info(_T("C:\\Temp\\file.dat"), _T("replacement.dat"));
    // replace the first file in the archive
    info.m_uReplaceIndex = 0;
    zip.AddNewFile(info);
    zip.Close();

Callbacks Called

• If a temporary archive is used (see above), then the CZipActionCallback::cbAdd callback is called while compressing a file to the temporary archive.
• If you have additionally specified CZipArchive::zipsmCheckForEff in CZipAddNewFileInfo::m_iSmartLevel and the compression to the temporary archive proved to be inefficient, then the file is stored instead in the temporary archive and this process calls the CZipActionCallback::cbAddStore callback.
• If the space size taken by the old file is different from the space size needed by the new file, the space needs to be adjusted for the new file to fit and this operation calls the CZipActionCallback::cbMoveData callback.

Renaming

• Use the CZipArchive::RenameFile() method to rename an existing file inside an archive.
  Sample Code

      CZipArchive zip;
      zip.Open(_T("C:\\Temp\\test.zip"));
      // rename the first file in the archive
      zip.RenameFile(0, _T("renamed.dat"));    
      zip.Close();
  

• If you have many files, you can also use the CZipArchive::GetFromArchive() methods for that. It may be faster than the CZipArchive::RenameFile() method.
  • Create a new archive.
  • Use, e.g. the
    CZipArchive::GetFromArchive(CZipArchive&,CZipIndexesArray&) method to move files that do not require renaming from the old archive to the new archive.
  • Use, e.g. the
    CZipArchive::GetFromArchive(CZipArchive&, ZIP_INDEX_TYPE) method to move files that require renaming and specify the new name as an argument.
  • Close the old archive and delete it.
  You will find some more information about using the CZipArchive::GetFromArchive() methods in Compressing Data.

Callback Called

If the sizes of the new and the old filenames differ, then the space inside the archive needs to be adjusted and this operation notifies about the progress using the CZipActionCallback::cbRename callback.

Deleting

You can delete files in an archive by specifying one of:

• an index of the file to delete with the method
  CZipArchive::RemoveFile(),
• an array of indexes of files to delete with the method
  CZipArchive::RemoveFiles(CZipIndexesArray&),
• an array of names of files to delete with the method
  CZipArchive::RemoveFiles(const CZipStringArray&).

If you plan to delete more files at once, use the methods that take arrays as arguments - they are optimized for multiple file deletion.

    CZipArchive zip;
    zip.Open(_T("C:\\Temp\\test.zip"));
    // delete the first file
    zip.RemoveFile(0);
    // delete two first files
    CZipIndexesArray indexes;
    indexes.Add(0);
    indexes.Add(1);
    zip.RemoveFiles(indexes);
    // delete files by their names
    CZipStringArray names;
    names.Add(_T("Temp\\file1.dat"));
    names.Add(_T("file4.dat"));
    zip.RemoveFiles(names);
    zip.Close();

Callbacks Called

• When a map of areas of data to be moved inside an archive is being calculated, the CZipActionCallback::cbDeleteCnt callback is called.
• When the space inside the archive needs to be adjusted, this operation notifies about the progress using the CZipActionCallback::cbDelete callback.

Changing the Modification Time of Files Inside an Archive

The modification time of the file is written in both local and central headers. To modify it, you need to update the time stamp in these both locations to keep the archive consistent. Follow the steps below to do it:

• Be sure that the existing local header information was already read from the archive. It happens when a file is opened for extraction, but you can also quickly update it by calling the CZipArchive::ReadLocalHeader() method.
• Request the CZipFileHeader object for the file which time stamp you want to change. Use the CZipArchive::GetFileInfo(ZIP_INDEX_TYPE) or CZipArchive::operator[]() methods.
• Change the time by calling the CZipFileHeader::SetTime() method.
• Write the local information back to the archive by calling the CZipArchive::OverwriteLocalHeader() method.
• To update the central directory, it first needs to be removed from the archive. The central directory is removed from an archive, when a modification such as adding, deleting, renaming, encrypting or other takes place. However, if you have not performed such a modification on the archive, you can call the CZipArchive::RemoveCentralDirectoryFromArchive() method to force the central directory removal.
  • You can check, if the central directory is currently in the archive by requesting the central directory information with the CZipArchive::GetCentralDirInfo() method and then examining the CZipCentralDir::CInfo::m_bInArchive value.
• The central directory is written to the archive when the archive is closed, but you can also force this by calling the CZipArchive::Flush() method.

    CZipArchive zip;
    zip.Open(_T("C:\\Temp\\test.zip"));
    int iIndexOfFile = 1;
    // read the local header information
    zip.ReadLocalHeader(iIndexOfFile);
    CZipFileHeader* pHeader = zip.GetFileInfo(iIndexOfFile);
    // set the time
    pHeader->SetTime(time(0));
    // write the local header information
    zip.OverwriteLocalHeader(iIndexOfFile);
    zip.RemoveCentralDirectoryFromArchive();
    // the central directory will be written back to the archive
    // during closing
    zip.Close();

Writing and Reading Global and File Comments

The ZipArchive Library provides methods to write and read global comments.

• To write a comment for the whole archive, use the
  CZipArchive::SetGlobalComment() method.
• To read a global comment from an existing archive, use the
  CZipArchive::GetGlobalComment() method.
• To write a comment for a single file in an archive, use the CZipArchive::SetFileComment() method.
• To read a file comment from an existing archive, use the CZipArchive::GetFileComment() method.