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208 lines
11 KiB
HTML
208 lines
11 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
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<html>
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<head>
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<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type">
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<style type="text/css"><!--
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BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}
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H1 {font-family: Verdana,Arial,Helvetica}
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H2 {font-family: Verdana,Arial,Helvetica}
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H3 {font-family: Verdana,Arial,Helvetica}
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A:link, A:visited, A:active { text-decoration: underline }
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--></style>
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<title>Upgrading 1.x code</title>
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</head>
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<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000">
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<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr>
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<td width="180">
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<a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a>
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</td>
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<td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center">
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<h1>The XML C library for Gnome</h1>
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<h2>Upgrading 1.x code</h2>
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</td></tr></table></td></tr></table></td>
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</tr></table>
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<table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr>
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<td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="index.html">Home</a></li>
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<li><a href="intro.html">Introduction</a></li>
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<li><a href="FAQ.html">FAQ</a></li>
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<li><a href="docs.html">Documentation</a></li>
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<li><a href="bugs.html">Reporting bugs and getting help</a></li>
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<li><a href="help.html">How to help</a></li>
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<li><a href="downloads.html">Downloads</a></li>
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<li><a href="news.html">News</a></li>
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<li><a href="XMLinfo.html">XML</a></li>
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<li><a href="XSLT.html">XSLT</a></li>
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<li><a href="python.html">Python and bindings</a></li>
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<li><a href="architecture.html">libxml architecture</a></li>
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<li><a href="tree.html">The tree output</a></li>
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<li><a href="interface.html">The SAX interface</a></li>
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<li><a href="xmldtd.html">Validation & DTDs</a></li>
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<li><a href="xmlmem.html">Memory Management</a></li>
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<li><a href="encoding.html">Encodings support</a></li>
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<li><a href="xmlio.html">I/O Interfaces</a></li>
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<li><a href="catalog.html">Catalog support</a></li>
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<li><a href="library.html">The parser interfaces</a></li>
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<li><a href="entities.html">Entities or no entities</a></li>
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<li><a href="namespaces.html">Namespaces</a></li>
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<li><a href="upgrade.html">Upgrading 1.x code</a></li>
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<li><a href="threads.html">Thread safety</a></li>
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<li><a href="DOM.html">DOM Principles</a></li>
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<li><a href="example.html">A real example</a></li>
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<li><a href="contribs.html">Contributions</a></li>
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<li>
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<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
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</li>
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</ul></td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="APIchunk0.html">Alphabetic</a></li>
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<li><a href="APIconstructors.html">Constructors</a></li>
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<li><a href="APIfunctions.html">Functions/Types</a></li>
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<li><a href="APIfiles.html">Modules</a></li>
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<li><a href="APIsymbols.html">Symbols</a></li>
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</ul></td></tr>
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</table>
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<table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul>
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<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
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<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
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<li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li>
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<li><a href="ftp://xmlsoft.org/">FTP</a></li>
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<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
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<li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li>
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<li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml">Bug Tracker</a></li>
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</ul></td></tr>
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</table>
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</td></tr></table></td>
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<td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd">
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<p>Incompatible changes:</p>
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<p>Version 2 of libxml is the first version introducing serious backward
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incompatible changes. The main goals were:</p>
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<ul>
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<li>a general cleanup. A number of mistakes inherited from the very early
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versions couldn't be changed due to compatibility constraints. Example
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the "childs" element in the nodes.</li>
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<li>Uniformization of the various nodes, at least for their header and link
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parts (doc, parent, children, prev, next), the goal is a simpler
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programming model and simplifying the task of the DOM implementors.</li>
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<li>better conformances to the XML specification, for example version 1.x
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had an heuristic to try to detect ignorable white spaces. As a result the
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SAX event generated were ignorableWhitespace() while the spec requires
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character() in that case. This also mean that a number of DOM node
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containing blank text may populate the DOM tree which were not present
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before.</li>
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</ul>
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<h3>How to fix libxml-1.x code:</h3>
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<p>So client code of libxml designed to run with version 1.x may have to be
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changed to compile against version 2.x of libxml. Here is a list of changes
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that I have collected, they may not be sufficient, so in case you find other
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change which are required, <a href="mailto:Daniel.<2E>eillardw3.org">drop me a
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mail</a>:</p>
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<ol>
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<li>The package name have changed from libxml to libxml2, the library name
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is now -lxml2 . There is a new xml2-config script which should be used to
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select the right parameters libxml2</li>
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<li>Node <strong>childs</strong> field has been renamed
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<strong>children</strong> so s/childs/children/g should be applied
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(probablility of having "childs" anywere else is close to 0+</li>
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<li>The document don't have anymore a <strong>root</strong> element it has
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been replaced by <strong>children</strong> and usually you will get a
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list of element here. For example a Dtd element for the internal subset
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and it's declaration may be found in that list, as well as processing
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instructions or comments found before or after the document root element.
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Use <strong>xmlDocGetRootElement(doc)</strong> to get the root element of
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a document. Alternatively if you are sure to not reference Dtds nor have
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PIs or comments before or after the root element
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s/->root/->children/g will probably do it.</li>
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<li>The white space issue, this one is more complex, unless special case of
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validating parsing, the line breaks and spaces usually used for indenting
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and formatting the document content becomes significant. So they are
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reported by SAX and if your using the DOM tree, corresponding nodes are
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generated. Too approach can be taken:
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<ol>
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<li>lazy one, use the compatibility call
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<strong>xmlKeepBlanksDefault(0)</strong> but be aware that you are
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relying on a special (and possibly broken) set of heuristics of
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libxml to detect ignorable blanks. Don't complain if it breaks or
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make your application not 100% clean w.r.t. to it's input.</li>
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<li>the Right Way: change you code to accept possibly unsignificant
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blanks characters, or have your tree populated with weird blank text
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nodes. You can spot them using the comodity function
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<strong>xmlIsBlankNode(node)</strong> returning 1 for such blank
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nodes.</li>
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</ol>
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<p>Note also that with the new default the output functions don't add any
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extra indentation when saving a tree in order to be able to round trip
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(read and save) without inflating the document with extra formatting
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chars.</p>
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</li>
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<li>The include path has changed to $prefix/libxml/ and the includes
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themselves uses this new prefix in includes instructions... If you are
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using (as expected) the
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<pre>xml2-config --cflags</pre>
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<p>output to generate you compile commands this will probably work out of
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the box</p>
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</li>
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<li>xmlDetectCharEncoding takes an extra argument indicating the lenght in
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byte of the head of the document available for character detection.</li>
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</ol>
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<h3>Ensuring both libxml-1.x and libxml-2.x compatibility</h3>
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<p>Two new version of libxml (1.8.11) and libxml2 (2.3.4) have been released
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to allow smoth upgrade of existing libxml v1code while retaining
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compatibility. They offers the following:</p>
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<ol>
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<li>similar include naming, one should use
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<strong>#include<libxml/...></strong> in both cases.</li>
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<li>similar identifiers defined via macros for the child and root fields:
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respectively <strong>xmlChildrenNode</strong> and
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<strong>xmlRootNode</strong>
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</li>
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<li>a new macro <strong>LIBXML_TEST_VERSION</strong> which should be
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inserted once in the client code</li>
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</ol>
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<p>So the roadmap to upgrade your existing libxml applications is the
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following:</p>
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<ol>
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<li>install the libxml-1.8.8 (and libxml-devel-1.8.8) packages</li>
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<li>find all occurences where the xmlDoc <strong>root</strong> field is
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used and change it to <strong>xmlRootNode</strong>
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</li>
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<li>similary find all occurences where the xmlNode <strong>childs</strong>
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field is used and change it to <strong>xmlChildrenNode</strong>
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</li>
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<li>add a <strong>LIBXML_TEST_VERSION</strong> macro somewhere in your
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<strong>main()</strong> or in the library init entry point</li>
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<li>Recompile, check compatibility, it should still work</li>
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<li>Change your configure script to look first for xml2-config and fallback
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using xml-config . Use the --cflags and --libs ouptut of the command as
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the Include and Linking parameters needed to use libxml.</li>
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<li>install libxml2-2.3.x and libxml2-devel-2.3.x (libxml-1.8.y and
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libxml-devel-1.8.y can be kept simultaneously)</li>
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<li>remove your config.cache, relaunch your configuration mechanism, and
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recompile, if steps 2 and 3 were done right it should compile as-is</li>
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<li>Test that your application is still running correctly, if not this may
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be due to extra empty nodes due to formating spaces being kept in libxml2
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contrary to libxml1, in that case insert xmlKeepBlanksDefault(1) in your
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code before calling the parser (next to
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<strong>LIBXML_TEST_VERSION</strong> is a fine place).</li>
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</ol>
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<p>Following those steps should work. It worked for some of my own code.</p>
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<p>Let me put some emphasis on the fact that there is far more changes from
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libxml 1.x to 2.x than the ones you may have to patch for. The overall code
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has been considerably cleaned up and the conformance to the XML specification
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has been drastically improved too. Don't take those changes as an excuse to
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not upgrade, it may cost a lot on the long term ...</p>
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<p><a href="bugs.html">Daniel Veillard</a></p>
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</td></tr></table></td></tr></table></td></tr></table></td>
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</tr></table></td></tr></table>
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</body>
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</html>
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