reading zip file.mht

symbian的学习笔记

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      <H2 class=3Dcontent-title>Reading ZIP File in Symbian OS<BR></H2>
      <DIV class=3Dbreadcrumb><A href=3D"http://www.newlc.com/">Home</A> =
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or a UIQ app). If you are new to Symbian, you should browse this section =
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      <DIV class=3Dspip-content>
      <P class=3Dspip>The most popular archive file format used these =
days is ZIP,=20
      originally created by Phil Katz from the modification of ARC =
format.=20
      Symbian OS provides a class, called CZipFile, to read ZIP file. =
This class=20
      is supported by Symbian since version 7.x. This article will show =
how to=20
      use CZipFile and give an example. You can compile and run the =
example in=20
      Series 60 2.x or UIQ 2.x.</P>
      <P class=3Dspip>Although CZipFile is documented in Symbian SDKs, =
the=20
      explanation is far from enough. Another challenge, there is no =
example how=20
      to use the class. That's why I write this article to share my =
experience=20
      reading ZIP file in Symbian OS. I hope this would be useful for =
you.</P>
      <H3 class=3Dspip>Reading ZIP File</H3>
      <P class=3Dspip>Let's start with a simple case, open a ZIP file =
and display=20
      information of all the files inside the ZIP file. Firstly, we need =
to=20
      create a new instance of CZipFile. There is a two-phase =
constructor that=20
      you can use to create it.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>CZipFile* zipFile =
=3D=20
      CZipFile::NewL(fileSession,=20
      aCompressedFile);<BR>CleanupStack::PushL(zipFile);</DIV></TT>
      <P></P>
      <P class=3Dspip>The first parameter of the constructor is a =
session of File=20
      Server. The second parameter is the file name of the ZIP file.</P>
      <P class=3Dspip>Next, we have to get the iterator for the ZIP file =
to=20
      iterate all the files one by one. It can be done by calling=20
      CZipFile::GetMembersL(). The return value is an instance of=20
      CZipFileMemberIterator class.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr =
align=3Dleft>CZipFileMemberIterator* members =3D=20
      =
zipFile-&gt;GetMembersL();<BR>CleanupStack::PushL(members);</DIV></TT>
      <P></P>
      <P class=3Dspip>Note that the ownership of members will be passed =
to the=20
      caller, thus we have to delete it after we are done.</P>
      <P class=3Dspip>Now, how can we get the instance of each file? By =
calling=20
      CZipFileMemberIterator::NextL(). We have to call this method until =
it=20
      returns 0, which means there is no more file. Look at the =
following=20
      example:</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>CZipFileMember* =
member;<BR>while=20
      ((member =3D members-&gt;NextL()) !=3D 0)<BR>&nbsp; &nbsp; &nbsp; =
&nbsp;=20
      {<BR>&nbsp; &nbsp; &nbsp; &nbsp; console-&gt;Printf(<BR>&nbsp; =
&nbsp;=20
      &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; KInfoMessage,<BR>&nbsp; =
&nbsp;=20
      &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
member-&gt;Name(),<BR>&nbsp;=20
      &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;=20
      member-&gt;CompressedSize(), member-&gt;UncompressedSize());&nbsp; =
&nbsp;=20
      &nbsp; &nbsp; <BR>&nbsp; &nbsp; &nbsp; &nbsp; delete =
member;<BR>&nbsp;=20
      &nbsp; &nbsp; &nbsp; }</DIV></TT>
      <P></P>
      <P class=3Dspip>The example above prints the name, compressed size =
and=20
      uncompressed size of all the files in the ZIP file. Note that we =
have to=20
      delete member because the ownership is passed to caller.</P>
      <P class=3Dspip>Finally, don't forget to release all the resources =
that we=20
      have allocated.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr =
align=3Dleft>CleanupStack::PopAndDestroy(); //=20
      members<BR>CleanupStack::PopAndDestroy(); // zipFile</DIV></TT>
      <P></P>
      <P class=3Dspip>If we have a ZIP file that contains three file, =
i.e.=20
      Example.txt, Example.dat and Example.png, the output will look =
like this=20
      (you can download this ZIP file at the end of this article).</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>Example.txt - 11 -=20
      11<BR>Example.dat - 15 - 180<BR>Example.png - 4393 - =
4393</DIV></TT>
      <P></P>
      <H3 class=3Dspip>Extracting a File from ZIP File</H3>
      <P class=3Dspip>This section shows how to extract a specific file =
from a ZIP=20
      file. As the previous example, the first step is to create the =
instance of=20
      CZipFile.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>CZipFile* zipFile =
=3D=20
      CZipFile::NewL(fileSession,=20
      aCompressedFile);<BR>CleanupStack::PushL(zipFile);</DIV></TT>
      <P></P>
      <P class=3Dspip>Here, we don't need an iterator because we are =
interested=20
      only in a specific file. The method that we have to call to get =
the=20
      instance of it is CZipFile::CaseInsensitiveMemberL(). This method =
requires=20
      a parameter, that is the file name that you want to access.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>CZipFileMember* =
member =3D=20
      =
zipFile-&gt;CaseInsensitiveMemberL(aFileName);<BR>CleanupStack::PushL(mem=
ber);</DIV></TT>
      <P></P>
      <P class=3Dspip>Once again, we have to delete member after we have =
finished=20
      using it. The next step is to the input stream and use the Read() =
method=20
      to extract the file. The input stream of a file inside ZIP file is =

      RZipFileMemberReaderStream. The method used to get the input =
stream is=20
      CZipFile::GetInputStreamL().</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr =
align=3Dleft>RZipFileMemberReaderStream*=20
      stream;<BR>zipFile-&gt;GetInputStreamL(member,=20
      stream);<BR>CleanupStack::PushL(stream);</DIV></TT>
      <P></P>
      <P class=3Dspip>The following code shows how to read the file. =
Before=20
      reading the file, the code allocates a buffer to store with the =
size of=20
      member-&gt;UncompressesedSize().</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>HBufC8* buffer =3D=20
      HBufC8::NewLC(member-&gt;UncompressedSize());<BR>TPtr8=20
      =
bufferPtr(buffer-&gt;Des());<BR>User::LeaveIfError(stream-&gt;Read(buffer=
Ptr,=20
      member-&gt;UncompressedSize()));</DIV></TT>
      <P></P>
      <P class=3Dspip>If your file is quite huge, do not use "one-shot" =
Read()=20
      like the example above. It is not good because it will block your =
program.=20
      Instead, read using a small block of buffer and do it inside an =
active=20
      object. This example use "one-shot" Read() for simplicity =
reason.</P>
      <P class=3Dspip>Now we have the extracted file in a buffer. You =
can use it=20
      right away, or alternatively you can write it to a file. Here is =
the=20
      example how to write it to a file.</P>
      <P class=3Dspip><TT></P>
      <DIV class=3Dspip_code dir=3Dltr align=3Dleft>RFile=20
      file;<BR>User::LeaveIfError(file.Replace(fileSession, fileName,=20
      =
EFileWrite));<BR>CleanupClosePushL(file);<BR>User::LeaveIfError(file.Writ=
e(*buffer));</DIV></TT>
      <P></P>
      <P class=3Dspip>Finally, do not forget to release all the =
allocated=20
      resources.</P>
      <P class=3Dspip><TT><SPAN class=3Dspip_code=20
      dir=3Dltr>CleanupStack::PopAndDestroy(5); // file, buffer, stream, =
member,=20
      zipFile</SPAN></TT></P>
      <H3 class=3Dspip>Example</H3>
      <P class=3Dspip>The following file contains the complete source =
code of the=20
      two examples above. This example is a console program. The output =
of the=20
      compiled example is a standalone .exe file, ZipExample.exe. Copy =
this file=20
      to your device at c:\systems\programs or any other directories. =
Before=20
      running the example, make sure that you have copied =
\group\Example.zip to=20
      c:\data\Example.zip on your device too.</P>
      <P class=3Dspip>The example does two things, i.e.: <BR><IMG =
class=3Dspip_puce=20
      alt=3D-=20
      =
src=3D"http://www.newlc.com/sites/all/themes/zen/images/blue_bullet.gif">=
&nbsp;&nbsp;Display=20
      information of all the files contained in c:\data\Example.zip. It =
is done=20
      in IteratorExampleL() function. <BR><IMG class=3Dspip_puce alt=3D- =

      =
src=3D"http://www.newlc.com/sites/all/themes/zen/images/blue_bullet.gif">=
&nbsp;&nbsp;Extract=20
      Example.txt from c:\data\Example.zip and save it to =
c:\data\Example.txt.=20
      It is done in ExtractionExampleL() function.</P>
      <P class=3Dspip><SPAN class=3Dinline_center><A=20
      title=3D"Download: ZipExample.zip (9.07 KB)"=20
      href=3D"http://www.newlc.com/files/ZipExample.zip"><IMG =
class=3Dinline=20
      title=3DZipExample.zip=20
      style=3D"BORDER-RIGHT: #6191c5 1px solid; BORDER-TOP: #6191c5 1px =
solid; BORDER-LEFT: #6191c5 1px solid; WIDTH: 48px; BORDER-BOTTOM: =
#6191c5 1px solid; HEIGHT: 48px"=20
      alt=3DZipExample.zip src=3D""></A><BR><A=20
      title=3D"Download: ZipExample.zip (9.07 KB)"=20
      =
href=3D"http://www.newlc.com/files/ZipExample.zip">ZipExample.zip</A></SP=
AN></P>
      <H3 class=3Dspip>Further Reading</H3>
      <P class=3Dspip><IMG class=3Dspip_puce alt=3D-=20
      =
src=3D"http://www.newlc.com/sites/all/themes/zen/images/blue_bullet.gif">=
&nbsp;&nbsp;<A=20
      class=3Dspip_out=20
      =
href=3D"http://www.pkware.com/business_and_developers/developer/appnote/"=
>.ZIP=20
      File Format Specification</A> - specification from the creator of =
PKZIP,=20
      the first program that supports ZIP file. <BR><IMG =
class=3Dspip_puce alt=3D-=20
      =
src=3D"http://www.newlc.com/sites/all/themes/zen/images/blue_bullet.gif">=
&nbsp;&nbsp;<A=20
      class=3Dspip_out=20
      =
href=3D"http://www.symbian.com/developer/techlib/v8.1adocs/doc_source/ref=
erence/reference-cpp/N102C2/CZipFileClass.html">CZipFile</A>=20
      - official documentation of class CZipFile from Symbian web=20
site.</P></DIV><!-- google_ad_section_end -->
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      <DIV class=3Dinfo><A=20
      href=3D"http://www.newlc.com/en/-Tutorials-.html">Tutorial</A> =
posted <ABBR=20
      class=3Dcreated title=3D2005-10-15T10:14:01+0100>October 15th, =
2005</ABBR> by=20
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develop C++ applications for this platform (no matter it is a Series 60 =
or a UIQ app). If you are new to Symbian, you should browse this section =
first !"=20
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