unzipdll.dll and unzipd32.dll version 2.06. See readme.txt for general
information on this DLLs.

How to call the functions:

To determine if a file is a ZIP file, use the following function:

function isZip(filename:pchar):boolean;

  This is a very simple test if a file is a ZIP-File.
  It only tests for the first for bytes being 'pk'#3#4,
  and also checks for self-extracting ZIP files.

If you want to know the DLL's version number, use

function GetUnzipDllVersion:word;

  This returns the Dll's main version in the high byte and the low
  version in the low byte (i.e. 2.0->2*256+0=512)

To find out which ZIP formats are supported, use

function GetSupportedMethods:longint;

  For version 0 (storing), bit 0 is set to indicate that version 0
  is supported. To test if a certain method is supported, use the
  following code:

  supported:=GetSupportedMethods and (1 shl method); {shl=shift left}

 ******************************************************************** 

To unzip files, one has to know first what files are in the ZIP file.
For making this very easy, three functions are included:

function GetFirstInZip(zipfilename:pchar;var zprec:tPackRec):integer;

  Works like findfirst: Given a zip file name and an empty structure
  of type tPackRec, GetFirstInZip fills the structure with the first
  entry of the central directory. The returned value is one of the
  constants zip_xxx. If this is zip_ok, the structure was filled
  with data. Otherwhise, the directory is empty or an error occured.
  Btw: This function reads the whole directory into one big block of
  64 k max. If it is bigger, the ZIP file is left open and additional
  blocks are read on successive GetNextInZip calls.

function GetNextInZip(var Zprec:tPackRec):integer;

  After a successful call to GetFirstInZip, additional entries of 
  the central directory can be read with this function. The structure
  Zprec must have been filled with GetFirstInZip, since it contains
  information on the ZIP file in the 'internal' field. Return value
  is the same as for GetFirstInZip. 

procedure CloseZipFile(var Zprec:tPackRec);

  After a loop of GetNextInZip, call this functions to free any
  buffers and to close the zip file.

tZipRec structure:

     tPackRec=record
       internal:array[0..7] of byte;  {Used internally by the dll}
       Time,                     {file time}
       Size,                     {file size}
       CompressSize,             {size in zipfile}
       headeroffset: Longint;    {file offset in zip: needed in unzipfile}
       FileName: tdirtype;       {file name}
       PackMethod: word;         {see below}
       Attr: word;               {file attribute}
       Flags: word;              {Only used by ARJ unpacker}
     end;

Example:
  rc:=GetFirstInZip('c:\test.zip',r);
  while rc=zip_ok do
    DosomethingWithData(r);
    rc:=GetNextInZip(r);
  end;
  closezipfile(r);

 ******************************************************************** 

To do the unzipping work, call the function unzip:

function unzipfile(in_name:pchar;out_name:pchar;attr:word;offset:longint;
  hFileAction:thandle;cm_index:integer):integer;

  in_name:      name of zip file with full path (i.e 'c:\test.zip')
  out_name:     desired name for unzipped file, existing files are overwritten
  attr:         File attribute, returned in tPackRec.Attr. Important to detect directories
  offset:       header position of desired file in zipfile, found in 
                tZiprec.headeroffset
  hFileAction:  handle to dialog box showing advance of decompression (optional),
                or zero when only keyboard shall be checked
  cm_index:     - if hfileaction<>0 : notification code sent in a wm_command
                  message to the dialog to update percent-bar
                - if hfileaction=0  : virtual key code of key the user must press
                  to interrupt unzipping, i.e. vk_escape
                  
  Return value: one of the unzip_xxx codes

Simplest unzipping loop, which will just unzip all files:

  rc:=GetFirstInZip(zipname,r);
  strcopy(target,'c:\');
  while rc=zip_ok do begin
    strcopy(buffer,target);
    strcat(buffer,r.Filename);
    if unzipfile(zipname,outpath,r.headeroffset,0,vk_escape)=unzip_ok then
      rc:=GetNextInZip(r)
    else rc:=zip_InternalError;
  end;
  closezipfile(r);

See zipinter.pas, the interface unit, for more details.