release/src/router/libxml2/doc/FAQ.html

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  10 </style><title>FAQ</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 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><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><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"><h1>The XML C parser and toolkit of Gnome</h1><h2>FAQ</h2></td></tr></table></td></tr></table></td></tr></table><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><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html">Home</a></li><li><a href="html/index.html">Reference Manual</a></li><li><a href="intro.html">Introduction</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="docs.html" style="font-weight:bold">Developer Menu</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="help.html">How to help</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="news.html">Releases</a></li><li><a href="XMLinfo.html">XML</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="xmldtd.html">Validation &amp; DTDs</a></li><li><a href="encoding.html">Encodings support</a></li><li><a href="catalog.html">Catalog support</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="contribs.html">Contributions</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="html/index.html" style="font-weight:bold">API Menu</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="ChangeLog.html">Recent Changes</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><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"><p>Table of Contents:</p><ul><li><a href="FAQ.html#License">License(s)</a></li>
  11   <li><a href="FAQ.html#Installati">Installation</a></li>
  12   <li><a href="FAQ.html#Compilatio">Compilation</a></li>
  13   <li><a href="FAQ.html#Developer">Developer corner</a></li>
  14 </ul><h3><a name="License" id="License">License</a>(s)</h3><ol><li><em>Licensing Terms for libxml</em>
  15     <p>libxml2 is released under the <a href="http://www.opensource.org/licenses/mit-license.html">MIT
  16     License</a>; see the file Copyright in the distribution for the precise
  17     wording</p>
  18   </li>
  19   <li><em>Can I embed libxml2 in a proprietary application ?</em>
  20     <p>Yes. The MIT License allows you to keep proprietary the changes you
  21     made to libxml, but it would be graceful to send-back bug fixes and
  22     improvements as patches for possible incorporation in the main
  23     development tree.</p>
  24   </li>
  25 </ol><h3><a name="Installati" id="Installati">Installation</a></h3><ol><li><strong><span style="background-color: #FF0000">Do Not Use
  26     libxml1</span></strong>, use libxml2</li>
  27   <p></p>
  28   <li><em>Where can I get libxml</em> ?
  29     <p>The original distribution comes from <a href="ftp://xmlsoft.org/libxml2/">xmlsoft.org</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/sources/libxml2/2.6/">gnome.org</a></p>
  30     <p>Most Linux and BSD distributions include libxml, this is probably the
  31     safer way for end-users to use libxml.</p>
  32     <p>David Doolin provides precompiled Windows versions at <a href="http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/         ">http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/</a></p>
  33   </li>
  34   <p></p>
  35   <li><em>I see libxml and libxml2 releases, which one should I install ?</em>
  36     <ul><li>If you are not constrained by backward compatibility issues with
  37         existing applications, install libxml2 only</li>
  38       <li>If you are not doing development, you can safely install both.
  39         Usually the packages <a href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a href="http://rpmfind.net/linux/RPM/libxml2.html">libxml2</a> are
  40         compatible (this is not the case for development packages).</li>
  41       <li>If you are a developer and your system provides separate packaging
  42         for shared libraries and the development components, it is possible
  43         to install libxml and libxml2, and also <a href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a>
  44         and <a href="http://rpmfind.net/linux/RPM/libxml2-devel.html">libxml2-devel</a>
  45         too for libxml2 &gt;= 2.3.0</li>
  46       <li>If you are developing a new application, please develop against
  47         libxml2(-devel)</li>
  48     </ul></li>
  49   <li><em>I can't install the libxml package, it conflicts with libxml0</em>
  50     <p>You probably have an old libxml0 package used to provide the shared
  51     library for libxml.so.0, you can probably safely remove it. The libxml
  52     packages provided on <a href="ftp://xmlsoft.org/libxml2/">xmlsoft.org</a> provide
  53     libxml.so.0</p>
  54   </li>
  55   <li><em>I can't install the libxml(2) RPM package due to failed
  56     dependencies</em>
  57     <p>The most generic solution is to re-fetch the latest src.rpm , and
  58     rebuild it locally with</p>
  59     <p><code>rpm --rebuild libxml(2)-xxx.src.rpm</code>.</p>
  60     <p>If everything goes well it will generate two binary rpm packages (one
  61     providing the shared libs and xmllint, and the other one, the -devel
  62     package, providing includes, static libraries and scripts needed to build
  63     applications with libxml(2)) that you can install locally.</p>
  64   </li>
  65 </ol><h3><a name="Compilatio" id="Compilatio">Compilation</a></h3><ol><li><em>What is the process to compile libxml2 ?</em>
  66     <p>As most UNIX libraries libxml2 follows the "standard":</p>
  67     <p><code>gunzip -c xxx.tar.gz | tar xvf -</code></p>
  68     <p><code>cd libxml-xxxx</code></p>
  69     <p><code>./configure --help</code></p>
  70     <p>to see the options, then the compilation/installation proper</p>
  71     <p><code>./configure [possible options]</code></p>
  72     <p><code>make</code></p>
  73     <p><code>make install</code></p>
  74     <p>At that point you may have to rerun ldconfig or a similar utility to
  75     update your list of installed shared libs.</p>
  76   </li>
  77   <li><em>What other libraries are needed to compile/install libxml2 ?</em>
  78     <p>Libxml2 does not require any other library, the normal C ANSI API
  79     should be sufficient (please report any violation to this rule you may
  80     find).</p>
  81     <p>However if found at configuration time libxml2 will detect and use the
  82     following libs:</p>
  83     <ul><li><a href="http://www.info-zip.org/pub/infozip/zlib/">libz</a> : a
  84         highly portable and available widely compression library.</li>
  85       <li>iconv: a powerful character encoding conversion library. It is
  86         included by default in recent glibc libraries, so it doesn't need to
  87         be installed specifically on Linux. It now seems a <a href="http://www.opennc.org/onlinepubs/7908799/xsh/iconv.html">part
  88         of the official UNIX</a> specification. Here is one <a href="http://www.gnu.org/software/libiconv/">implementation of the
  89         library</a> which source can be found <a href="ftp://ftp.ilog.fr/pub/Users/haible/gnu/">here</a>.</li>
  90     </ul></li>
  91   <p></p>
  92   <li><em>Make check fails on some platforms</em>
  93     <p>Sometimes the regression tests' results don't completely match the
  94     value produced by the parser, and the makefile uses diff to print the
  95     delta. On some platforms the diff return breaks the compilation process;
  96     if the diff is small this is probably not a serious problem.</p>
  97     <p>Sometimes (especially on Solaris) make checks fail due to limitations
  98     in make. Try using GNU-make instead.</p>
  99   </li>
 100   <li><em>I use the SVN version and there is no configure script</em>
 101     <p>The configure script (and other Makefiles) are generated. Use the
 102     autogen.sh script to regenerate the configure script and Makefiles,
 103     like:</p>
 104     <p><code>./autogen.sh --prefix=/usr --disable-shared</code></p>
 105   </li>
 106   <li><em>I have troubles when running make tests with gcc-3.0</em>
 107     <p>It seems the initial release of gcc-3.0 has a problem with the
 108     optimizer which miscompiles the URI module. Please use another
 109     compiler.</p>
 110   </li>
 111 </ol><h3><a name="Developer" id="Developer">Developer</a> corner</h3><ol><li><em>Troubles compiling or linking programs using libxml2</em>
 112     <p>Usually the problem comes from the fact that the compiler doesn't get
 113     the right compilation or linking flags. There is a small shell script
 114     <code>xml2-config</code> which is installed as part of libxml2 usual
 115     install process which provides those flags. Use</p>
 116     <p><code>xml2-config --cflags</code></p>
 117     <p>to get the compilation flags and</p>
 118     <p><code>xml2-config --libs</code></p>
 119     <p>to get the linker flags. Usually this is done directly from the
 120     Makefile as:</p>
 121     <p><code>CFLAGS=`xml2-config --cflags`</code></p>
 122     <p><code>LIBS=`xml2-config --libs`</code></p>
 123   </li>
 124   <li><em>I want to install my own copy of libxml2 in my home directory and
 125     link my programs against it, but it doesn't work</em>
 126     <p>There are many different ways to accomplish this.  Here is one way to
 127     do this under Linux.  Suppose your home directory is <code>/home/user.
 128     </code>Then:</p>
 129     <ul><li>Create a subdirectory, let's call it <code>myxml</code></li>
 130       <li>unpack the libxml2 distribution into that subdirectory</li>
 131       <li>chdir into the unpacked distribution
 132         (<code>/home/user/myxml/libxml2 </code>)</li>
 133       <li>configure the library using the "<code>--prefix</code>" switch,
 134         specifying an installation subdirectory in
 135         <code>/home/user/myxml</code>, e.g.
 136         <p><code>./configure --prefix /home/user/myxml/xmlinst</code> {other
 137         configuration options}</p>
 138       </li>
 139       <li>now run <code>make</code> followed by <code>make install</code></li>
 140       <li>At this point, the installation subdirectory contains the complete
 141         "private" include files, library files and binary program files (e.g.
 142         xmllint), located in
 143         <p><code>/home/user/myxml/xmlinst/lib,
 144         /home/user/myxml/xmlinst/include </code> and <code>
 145         /home/user/myxml/xmlinst/bin</code></p>
 146         respectively.</li>
 147       <li>In order to use this "private" library, you should first add it to
 148         the beginning of your default PATH (so that your own private program
 149         files such as xmllint will be used instead of the normal system
 150         ones).  To do this, the Bash command would be
 151         <p><code>export PATH=/home/user/myxml/xmlinst/bin:$PATH</code></p>
 152       </li>
 153       <li>Now suppose you have a program <code>test1.c</code> that you would
 154         like to compile with your "private" library.  Simply compile it using
 155         the command
 156         <p><code>gcc `xml2-config --cflags --libs` -o test test.c</code></p>
 157         Note that, because your PATH has been set with <code>
 158         /home/user/myxml/xmlinst/bin</code> at the beginning, the xml2-config
 159         program which you just installed will be used instead of the system
 160         default one, and this will <em>automatically</em> get the correct
 161         libraries linked with your program.</li>
 162     </ul></li>
 163
 164   <p></p>
 165   <li><em>xmlDocDump() generates output on one line.</em>
 166     <p>Libxml2 will not <strong>invent</strong> spaces in the content of a
 167     document since <strong>all spaces in the content of a document are
 168     significant</strong>. If you build a tree from the API and want
 169     indentation:</p>
 170     <ol><li>the correct way is to generate those yourself too.</li>
 171       <li>the dangerous way is to ask libxml2 to add those blanks to your
 172         content <strong>modifying the content of your document in the
 173         process</strong>. The result may not be what you expect. There is
 174         <strong>NO</strong> way to guarantee that such a modification won't
 175         affect other parts of the content of your document. See <a href="http://xmlsoft.org/html/libxml-parser.html#xmlKeepBlanksDefault">xmlKeepBlanksDefault
 176         ()</a> and <a href="http://xmlsoft.org/html/libxml-tree.html#xmlSaveFormatFile">xmlSaveFormatFile
 177         ()</a></li>
 178     </ol></li>
 179   <p></p>
 180   <li><em>Extra nodes in the document:</em>
 181     <p><em>For an XML file as below:</em></p>
 182     <pre>&lt;?xml version="1.0"?&gt;
 183 &lt;PLAN xmlns="http://www.argus.ca/autotest/1.0/"&gt;
 184 &lt;NODE CommFlag="0"/&gt;
 185 &lt;NODE CommFlag="1"/&gt;
 186 &lt;/PLAN&gt;</pre>
 187     <p><em>after parsing it with the function
 188     pxmlDoc=xmlParseFile(...);</em></p>
 189     <p><em>I want to the get the content of the first node (node with the
 190     CommFlag="0")</em></p>
 191     <p><em>so I did it as following;</em></p>
 192     <pre>xmlNodePtr pnode;
 193 pnode=pxmlDoc-&gt;children-&gt;children;</pre>
 194     <p><em>but it does not work. If I change it to</em></p>
 195     <pre>pnode=pxmlDoc-&gt;children-&gt;children-&gt;next;</pre>
 196     <p><em>then it works.  Can someone explain it to me.</em></p>
 197     <p></p>
 198     <p>In XML all characters in the content of the document are significant
 199     <strong>including blanks and formatting line breaks</strong>.</p>
 200     <p>The extra nodes you are wondering about are just that, text nodes with
 201     the formatting spaces which are part of the document but that people tend
 202     to forget. There is a function <a href="http://xmlsoft.org/html/libxml-parser.html">xmlKeepBlanksDefault
 203     ()</a>  to remove those at parse time, but that's an heuristic, and its
 204     use should be limited to cases where you are certain there is no
 205     mixed-content in the document.</p>
 206   </li>
 207   <li><em>I get compilation errors of existing code like when accessing
 208     <strong>root</strong> or <strong>child fields</strong> of nodes.</em>
 209     <p>You are compiling code developed for libxml version 1 and using a
 210     libxml2 development environment. Either switch back to libxml v1 devel or
 211     even better fix the code to compile with libxml2 (or both) by <a href="upgrade.html">following the instructions</a>.</p>
 212   </li>
 213   <li><em>I get compilation errors about non existing
 214     <strong>xmlRootNode</strong> or <strong>xmlChildrenNode</strong>
 215     fields.</em>
 216     <p>The source code you are using has been <a href="upgrade.html">upgraded</a> to be able to compile with both libxml
 217     and libxml2, but you need to install a more recent version:
 218     libxml(-devel) &gt;= 1.8.8 or libxml2(-devel) &gt;= 2.1.0</p>
 219   </li>
 220   <li><em>Random crashes in threaded applications</em>
 221     <p>Read and follow all advices on the <a href="threads.html">thread
 222     safety</a> page, and make 100% sure you never call xmlCleanupParser()
 223     while the library or an XML document might still be in use by another
 224     thread.</p>
 225   </li>
 226   <li><em>The example provided in the web page does not compile.</em>
 227     <p>It's hard to maintain the documentation in sync with the code
 228     &lt;grin/&gt; ...</p>
 229     <p>Check the previous points 1/ and 2/ raised before, and please send
 230     patches.</p>
 231   </li>
 232   <li><em>Where can I get more examples and information than provided on the
 233     web page?</em>
 234     <p>Ideally a libxml2 book would be nice. I have no such plan ... But you
 235     can:</p>
 236     <ul><li>check more deeply the <a href="html/libxml-lib.html">existing
 237         generated doc</a></li>
 238       <li>have a look at <a href="examples/index.html">the set of
 239         examples</a>.</li>
 240       <li>look for examples of use for libxml2 function using the Gnome code
 241           or by asking on Google.</li>
 242       <li><a href="http://svn.gnome.org/viewvc/libxml2/trunk/">Browse
 243         the libxml2 source</a> , I try to write code as clean and documented
 244         as possible, so looking at it may be helpful. In particular the code
 245         of <a href="http://svn.gnome.org/viewvc/libxml2/trunk/xmllint.c?view=markup">xmllint.c</a> and of the various testXXX.c test programs should
 246         provide good examples of how to do things with the library.</li>
 247     </ul></li>
 248   <p></p>
 249   <li><em>What about C++ ?</em>
 250     <p>libxml2 is written in pure C in order to allow easy reuse on a number
 251     of platforms, including embedded systems. I don't intend to convert to
 252     C++.</p>
 253     <p>There is however a C++ wrapper which may fulfill your needs:</p>
 254     <ul><li>by Ari Johnson &lt;ari@btigate.com&gt;:
 255         <p>Website: <a href="http://libxmlplusplus.sourceforge.net/">http://libxmlplusplus.sourceforge.net/</a></p>
 256         <p>Download: <a href="http://sourceforge.net/project/showfiles.php?group_id=12999">http://sourceforge.net/project/showfiles.php?group_id=12999</a></p>
 257       </li>
 258     </ul></li>
 259   <li><em>How to validate a document a posteriori ?</em>
 260     <p>It is possible to validate documents which had not been validated at
 261     initial parsing time or documents which have been built from scratch
 262     using the API. Use the <a href="http://xmlsoft.org/html/libxml-valid.html#xmlValidateDtd">xmlValidateDtd()</a>
 263     function. It is also possible to simply add a DTD to an existing
 264     document:</p>
 265     <pre>xmlDocPtr doc; /* your existing document */
 266 xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */
 267
 268         dtd-&gt;name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */
 269
 270         doc-&gt;intSubset = dtd;
 271         if (doc-&gt;children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd);
 272         else xmlAddPrevSibling(doc-&gt;children, (xmlNodePtr)dtd);
 273           </pre>
 274   </li>
 275   <li><em>So what is this funky "xmlChar" used all the time?</em>
 276     <p>It is a null terminated sequence of utf-8 characters. And only utf-8!
 277     You need to convert strings encoded in different ways to utf-8 before
 278     passing them to the API.  This can be accomplished with the iconv library
 279     for instance.</p>
 280   </li>
 281   <li>etc ...</li>
 282 </ol><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>