Problem with namespace and libxml when i use Xpath

Question

hi

i've got a problem when i'm using libxml with XPath. I want to parse an youtube playlist :

<?xml version='1.0' encoding='UTF-8'?>
<feed xmlns='http://www.w3.org/2005/Atom'
  xmlns:openSearch='http://a9.com/-/spec/opensearch/1.1/'
  xmlns:media='http://search.yahoo.com/mrss/'
  xmlns:batch='http://schemas.google.com/gdata/batch'
  xmlns:yt='http://gdata.youtube.com/schemas/2007'
  xmlns:gd='http://schemas.google.com/g/2005'
  gd:etag='W/&quot;Dk8DRn47eCp7ImA9WxRQGEk.&quot;'>
  <id>tag:youtube,2008:user:andyland74:playlists</id>
  <updated>2008-07-21T16:43:25.232Z</updated>
  <category scheme='http://schemas.google.com/g/2005#kind'
    term='http://gdata.youtube.com/schemas/2007#playlistLink'/&gt;
  <title>Playlists of andyland74</title>
  <logo>http://www.youtube.com/img/pic_youtubelogo_123x63.gif&lt;/logo&gt;
  <link rel='related' type='application/atom+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74?v=2'/&gt;
  <link rel='alternate' type='text/html'
    href='http://www.youtube.com/profile_play_list?user=andyland74'/&gt;
  <link rel='http://schemas.google.com/g/2005#feed'
    type='application/atom+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists?v=2'/&gt;
  <link rel='http://schemas.google.com/g/2005#post'
    type='application/atom+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists?v=2'/&gt;
  <link rel='http://schemas.google.com/g/2005#batch'
    type='application/atom+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists/batch?v=2'/&gt;
  <link rel='self' type='application/atom+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists?...'/&gt;
  <link rel='service' type='application/atomsvc+xml'
    href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists?alt=...'/&gt;
  <author>
    <name>andyland74</name>
    <uri>http://gdata.youtube.com/feeds/api/users/andyland74&lt;/uri&gt;
  </author>
  <generator version='2.0'
    uri='http://gdata.youtube.com/'&gt;YouTube data API</generator>
  <openSearch:totalResults>3</openSearch:totalResults>
  <openSearch:startIndex>1</openSearch:startIndex>
  <openSearch:itemsPerPage>25</openSearch:itemsPerPage>
  <entry gd:etag='W/&quot;Dk8DRn47eCp7ImA9WxRQGEk.&quot;'>
    <id>tag:youtube,2008:user:andyland74:playlist:8BCDD04DE8F771B2</id>
    <published>2007-11-04T17:30:27.000-08:00</published>
    <updated>2008-07-15T12:33:20.000-07:00</updated>
    <app:edited xmlns:app='http://www.w3.org/2007/app'&gt;2008-07-15T12:33:20.000-07:00&lt;/app:edited&gt;
    <category scheme='http://schemas.google.com/g/2005#kind'
      term='http://gdata.youtube.com/schemas/2007#playlistLink'/&gt;
    <title>My New Playlist Title</title>
    <summary>My new playlist Description</summary>
    <content type='application/atom+xml;type=feed'
      src='http://gdata.youtube.com/feeds/api/playlists/8BCDD04DE8F771B2?v=2'/&gt;
    <link rel='related' type='application/atom+xml'
      href='http://gdata.youtube.com/feeds/api/users/andyland74?v=2'/&gt;
    <link rel='alternate' type='text/html'
      href='http://www.youtube.com/view_play_list?p=8BCDD04DE8F771B2'/&gt;
    <link rel='self' type='application/atom+xml'
      href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists/8BCDD04DE8F771B2?v=2'/&gt;
    <link rel='edit' type='application/atom+xml'
      href='http://gdata.youtube.com/feeds/api/users/andyland74/playlists/8BCDD04DE8F771B2?v=2'/&gt;
    <author>
      <name>andyland74</name>
      <uri>http://gdata.youtube.com/feeds/api/users/andyland74&lt;/uri&gt;
    </author>
    <yt:countHint>9</yt:countHint>
  </entry>
</feed>

when i use the following xpath expression "/feed", the xmlXPathEvalExpression say me that i doesnt find.

if i remove all the xmlns attributes of feed it works. How could i make it work even with xmlns attributes ?

i use libxml with objective-C

Answer 1

You didn't post your query code, but it sounds like you aren't registering the namespaces with your XpathContext. Here's the API docs for xmlXPathRegisterNS, I believe it will do what you're looking for. It won't let you register a default namespace, so you'll need to change your XPath expression to /feed:feed or the like.

Answer 2

ok for xmlXpathRegisterNS function. But why i can't register a default namespace ?

why should i use /feed:feed expression if i just want to get ?

Answer 3

To use a default namespace just register the namespace xlmns= and then use /xmlns:feed in your query.