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Modification of Archives: Replacing, Renaming, Deleting and Changing Data
Applies To: All But Multi-Segment Archives

Introduction

Replacing

Sample Code
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

Deleting

You can delete files in an archive by specifying either of: If you plan to delete more files at once, use the methods that take arrays as arguments - they are optimized for multiple file deletion.

If you don't want to physically remove the file from the archive, but only from the central directory (e.g. to save the processing time or for safer archive modifications), use the CZipArchive::RemoveFile method and set the bRemoveData parameter to false.

Sample Code
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

Committing Modification Changes

  • Commit changes functionality currently concerns only renaming of files.
  • The ZipArchive Library allows grouping multiple operations and writing the necessary changes to an archive at once, which is more efficient than modifying files separately.
  • To examine, if a file has been modified, call the CZipFileHeader::IsModified() method.
  • To examine, if there are any pending modification in an archive, call the CZipArchive::IsModified() method.

Commit Mode

Callback Called

If data sizes of modified files differ after modifications, then the space inside the archive needs to be adjusted and the CZipArchive::CommitChanges() method notifies about the progress using the CZipActionCallback::cbModify callback.
Sample Code
CZipArchive zip;
zip.Open(_T("C:\\Temp\\test.zip"));
zip.SetCommitMode(CZipArchive::cmManual);
// rename the first file in the archive
zip[0]->SetFileName(_T("renamed.dat"));
zip[2]->SetFileName(_T("renamed2.dat"));
zip.CommitChanges();
// perform possibly some other operations
zip.Close();

Renaming

Sample Code
CZipArchive zip;
zip.Open(_T("C:\\Temp\\test.zip"));
zip.SetCommitMode(CZipArchive::cmManual);
// rename the first file in the archive
zip[0]->SetFileName(_T("renamed.dat"));
zip[2]->SetFileName(_T("renamed2.dat"));
// this will call CommitChanges
zip.Close();

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:
Sample Code
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->SetModificationTime(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();

Storing Modification, Creation and Last Access File Time (High Resolution)

The default file modification time has 2 seconds resolution. To store the modification time in full resolution and additionally store creation and last access times, call the CZipArchive::SetFullFileTimes() method after opening an archive. It will affect all files added afterwards to the archive.
  • The file times storage format is compatible with other software (e.g. WinZip) and the software that doesn't support it, will just use the regular modification time stored inside of the archive the standard way.
  • The information is stored inside of an extra header in the central directory only, so modification of the high resolution file times doesn't need the local header to be removed. Only the central directory needs to be updated (see Modification of Archives: Replacing, Renaming, Deleting and Changing Data for more information). However, when updating the modification time, it is recommended to update the local header as well (as described previously) to keep the standard modification time in sync with the high resolution time, so that the software that doesn't support the high resolution times can still set the modification time properly.
  • To set modification time in full resolution for an existing file inside of an archive, use the CZipFileHeader::SetModificationTime() method and set the bFullResolution parameter to true. To set other file times, use CZipFileHeader::SetLastAccessTime() and CZipFileHeader::SetCreationTime() methods.
  • Windows - Some file systems do not support full resolution file times, so the accuracy may be lost when extracting such a file.
    • NT FAT - modification time has a resolution of 2 seconds, create time - 10 ms and last access time - 1 day.
    • NTFS - last access time has a resolution of 1 hour.
    • See File Times for more information.
  • Linux does not store the file creation time.
Sample Code
CZipArchive zip;
zip.Open(_T("C:\\Temp\\test.zip"));
CZipFileHeader* pHeader = zip.GetFileInfo(0);
pHeader->SetLastAccessTime(time(0));
zip.SetFullFileTimes();
// add a new file, it will have full file times stored
zip.AddNewFile(_T("C:\\Temp\\file.dat"));
zip.RemoveCentralDirectoryFromArchive();
// the central directory will be written back to the archive
// during closing
zip.Close();

Writing and Reading File and Archive Comments

The ZipArchive Library provides the following methods to write and read comments.

Controlling Windows System File Cache

When performing extensive file operations (especially on large files under a 64-bit system) you may notice that large amount of memory is being used. This is may be related to the growing size of Windows System File Cache. Resolving of the issue is beyond the scope of the ZipArchive Library, but here are possible solutions: Some more information can be also found for example in these articles:
Article ID: 0610231944
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