Question

I’m trying to utilize “7za.dll” together with this Delphi wrapper – http://www.progdigy.com/?page_id=13

Having difficulties translating this code to C++ and understanding the wrapper itself:

procedure TMainForm.ExtractAllClick(Sender: TObject);
  var Arch: I7zOutArchive;
begin
  Arch := CreateOutArchive(CLSID_CFormat7z);
  // add a file
  Arch.AddFile('c:\test.bin', 'folder\test.bin');
  // add files using willcards and recursive search
  Arch.AddFiles('c:\test', 'folder', '*.pas;*.dfm', true);
  // add a stream
  Arch.AddStream(aStream, soReference, faArchive, CurrentFileTime, CurrentFileTime, 'folder\test.bin', false, false);
  // compression level
  SetCompressionLevel(Arch, 5);
  // compression method if <> LZMA
  SevenZipSetCompressionMethod(Arch, m7BZip2);
  // add a progress bar ...
  Arch.SetProgressCallback(...);
  // set a password if necessary
  Arch.SetPassword('password');
  // Save to file
  Arch.SaveToFile('c:\test.zip');
  // or a stream
  Arch.SaveToStream(aStream);
end;

I’ve made additional wrapper of wrapper Delphi unit which when included in C++ code wraps above and it works. Now I’d like to use it a step further – call the above in C++ code directly.

How do I initialize, construct and release this I7zOutArchive interface properly in C++?

Is there a need to destroy (free memory) in above code or is it automatic when it goes out of scope (I usually use boost::scoped_ptr to do the job, is something like that required here)?

Answer 1

You do need to destroy the thing returned by CreateOutArchive, but scoped_ptr would be inappropriate. Instead, use the built-in System::DelphiInterface class:

System::DelphiInterface<I7zOutArchive> Arch = CreateOutArchive(CLSID_CFormat7z);

Then, call methods on that object the same as you would any other COM interface. (Replace Delphi’s . operator with ->, and you’re most of the way there.) The object will get destroyed when the reference count reaches zero, which generally occurs when Arch goes out of scope.