zlib用法

uses

  zlib;

//将Src使用Zlib压缩后存入Dst当中

procedure PackStream(const Src:TStream; Dst:TStream);

var

  CompStream: TCompressionStream;

begin

  //增加“断言”以防止输入参数有误

  Assert(Src <> Nil);

  Assert(Dst <> Nil);

  CompStream := TCompressionStream.Create(clDefault,Dst);

  try

    //将源数据的偏移转到首部

    Src.Seek(0,soFromBeginning);

    //使用CopyFrom将源数据输入到压缩流，以实现压缩

    CompStream.CopyFrom(Src,0);

  finally

    CompStream.Free;

  end;

end;

//将以zlib压缩的Src解压缩后存入Dst当中

procedure UnpackStream(const Src:TStream; Dst:TStream);

var

  DecompStream: TDecompressionStream;

  NewSize: Int64;

begin

  //增加“断言”以防止输入参数有误

  Assert(Src <> Nil);

  Assert(Dst <> Nil);

  DecompStream:= TDecompressionStream.Create(Src);

  try

    //将源数据的偏移转到首部

    NewSize := Src.Seek(0, soFromEnd);

    Src.Seek(0, soFromBeginning);

    //使用CopyFrom将源数据输入到解压缩流，以实现解压缩

    //并得到实际解压缩后的数据大小(NewSize)

    //内部会使用AllocMem(System单元定义)对Dst进行内存重新分配

    //所以，Dst的内存管理必须兼容AllocMem进行内存分配

    NewSize := Dst.CopyFrom(DecompStream,NewSize);

    //重新设置Dst的实际大小(已经在解压缩过程当中进行重新分配)

    Dst.Size := NewSize;

  finally

    DecompStream.Free;

  end;

end;

//测试代码

procedure Test;

var

  SrcStream,PackedStream,UnpackedStream:TMemoryStream;

begin

  SrcStream := TMemoryStream.Create;

  try

    SrcStream.LoadFromFile('c:/test.xml');

    PackedStream := TMemoryStream.Create;

    try

      //压缩

      PackStream(SrcStream, PackedStream);

      PackedStream.Seek(0, soFromBeginning);

      PackedStream.SaveToFile('c:/test_xml.pk');

      UnpackedStream := TMemoryStream.Create;

      try

        //解压缩

        UnpackStream(PackedStream, UnpackedStream);

        UnpackedStream.Seek(0, soFromBeginning);

        UnpackedStream.SaveToFile('c:/test_xml.xml');

      finally

        UnpackedStream.Free;

      end;

    finally

      PackedStream.Free;

    end;

  finally

    SrcStream.Free;

  end;

end;