Introduction

• The ZipArchive Library allows the following operations in memory:
  • opening archives for creation and modification,
  • compressing memory files,
  • extracting files from archive to memory files.
  This allows the whole archive processing to be performed entirely in memory.
• The CZipMemFile object is not destroyed throughout the whole processing.
• Note that it is not an error to set the file pointer in the CZipMemFile object to a position beyond the end of the file.

In-Memory Archive Creating and Opening

To create or open an archive in memory, use the CZipArchive::Open(CZipAbstractFile&) method and pass CZipMemFile object as an argument.

Creating

If you are creating a new archive, the memory file will hold the resulting archive.

• To clear the contents of the memory file before creating a new archive, open the archive using the CZipArchive::zipCreate mode.
• To keep the contents of the memory file and append the archive at the end of it, open the archive using the CZipArchive::zipCreateAppend mode.

    CZipMemFile mf;
    CZipArchive zip;    
    // create the archive in memory
    zip.Open(mf, CZipArchive::zipCreate);
    // add a file
    zip.AddNewFile(_T("C:\\Temp\\file.dat"));
    zip.Close();
    // let's write the archive to the disk
    CZipFile f;
    if (f.Open(_T("C:\\Temp\\test.zip"), 
        CZipFile::modeWrite | CZipFile::modeCreate, false))
    {
        int iLen = (int)mf.GetLength();
        BYTE* b = mf.Detach();
        f.Write(b, iLen);
        f.Close();
        // we must free the detached memory
        free(b);
    }

Opening

If you are opening an existing archive, the memory file should already hold an archive.

    CZipFile f;
    if (f.Open(_T("C:\\Temp\\test.zip"), CZipFile::modeRead, false))
    {
        // read the contents of the file into the memory file
        int iLen = (int)f.GetLength();    
        BYTE* b = (BYTE*)malloc((UINT)iLen);
        f.Read(b, iLen);
        f.Close();
        CZipMemFile mf;
        mf.Attach(b, iLen);
        // open the archive in memory
        CZipArchive zip;
        zip.Open(mf);
        zip.ExtractFile(0, _T("C:\\Temp"));
        zip.Close();
    }

In-Memory Data Compressing and Extracting

• To compress a memory file, use one of the following methods:
  • CZipArchive::AddNewFile(CZipAbstractFile&, LPCTSTR),
  • CZipArchive::AddNewFile(CZipAddNewFileInfo&)
• To extract a file in an archive to a memory file, use the
  CZipArchive::ExtractFile(ZIP_INDEX_TYPE, CZipAbstractFile&) method.

    LPCTSTR zipFileName = _T("C:\\Temp\\test.zip");
    CZipArchive zip;
    zip.Open(zipFileName, CZipArchive::zipCreate);
    CZipMemFile mf;
    // prepare the memory file
    LPCTSTR data1 = _T("Test data");
    mf.Write(data1, (DWORD)(_tcslen(data1) * sizeof(TCHAR)));
    // compress the memory data
    zip.AddNewFile(mf, _T("file1.txt"));
    zip.Close();    
    zip.Open(zipFileName);
    // reset the contents of the CZipMemFile object
    mf.SetLength(0);
    // extract the contents of the file into memory
    zip.ExtractFile(0, mf);
    zip.Close();
    // print the contents of the extracted data
    BYTE* b = mf.Detach();
    _tprintf((LPCTSTR)b);
    // we must free the detached memory
    free(b);

See Also API Links

• CZipArchive::Open(CZipAbstractFile&)
• CZipArchive::AddNewFile(CZipAbstractFile&, LPCTSTR)
• CZipArchive::ExtractFile(ZIP_INDEX_TYPE, CZipAbstractFile&)
• CZipArchive::Close()