Libxml Frequently Asked Questions

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Version: $Revision: 1.16 $

Table of Content:

Licence(s)

  1. Licensing Terms for libxml

    libxml is released under 2 (compatible) licences:

  2. Can I embed libxml in a proprietary application ?

    Yes. The W3C IPR allows you to also keep proprietary the changes you made to libxml, but it would be graceful to provide back bugfixes and improvements as patches for possible incorporation in the main development tree

Installation

  1. Unless you are forced to because your application links with a Gnome library requiring it, Do Not Use libxml1, use libxml2
  2. Where can I get libxml ?

    The original distribution comes from rpmfind.net or gnome.org

    Most linux and Bsd distribution includes libxml, this is probably the safer way for end-users

    David Doolin provides precompiled Windows versions at http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/

  3. I see libxml and libxml2 releases, which one should I install ?
  4. I can't install the libxml package it conflicts with libxml0

    You probably have an old libxml0 package used to provide the shared library for libxml.so.0, you can probably safely remove it. Anyway the libxml packages provided on rpmfind.net provides libxml.so.0

  5. I can't install the libxml(2) RPM package due to failed dependancies

    The most generic solution is to refetch the latest src.rpm , and rebuild it locally with

    rpm --rebuild libxml(2)-xxx.src.rpm

    if everything goes well it will generate two binary rpm (one providing the shared libs and xmllint, and the other one, the -devel package providing includes, static libraries and scripts needed to build applications with libxml(2)) that you can install locally.

Compilation

  1. What is the process to compile libxml ?

    As most UNIX libraries libxml follows the "standard":

    gunzip -c xxx.tar.gz | tar xvf -

    cd libxml-xxxx

    ./configure --help

    to see the options, then the compilation/installation proper

    ./configure [possible options]

    make

    make install

    At that point you may have to rerun ldconfig or similar utility to update your list of installed shared libs.

  2. What other libraries are needed to compile/install libxml ?

    Libxml does not requires any other library, the normal C ANSI API should be sufficient (please report any violation to this rule you may find).

    However if found at configuration time libxml will detect and use the following libs:

  3. libxml does not compile with HP-UX's optional ANSI-C compiler

    this is due to macro limitations. Try to add " -Wp,-H16800 -Ae" to the CFLAGS

    you can also install and use gcc instead or use a precompiled version of libxml, both available from the HP-UX Porting and Archive Centre

  4. make check fails on some platforms

    Sometime the regression tests results don't completely match the value produced by the parser, and the makefile uses diff to print the delta. On some platforms the diff return breaks the compilation process, if the diff is small this is probably not a serious problem

  5. I use the CVS version and there is no configure script

    The configure (and other Makefiles) are generated. Use the autogen.sh script to regenerate the configure and Makefiles, like:

    ./autogen.sh --prefix=/usr --disable-shared

  6. I have troubles when running make tests with gcc-3.0

    It seems the initial release of gcc-3.0 has a problem with the optimizer which miscompiles the URI module. Please use another compiler

Developer corner

  1. xmlDocDump() generates output on one line

    libxml will not invent spaces in the content of a document since all spaces in the content of a document are significant. If you build a tree from the API and want indentation:

    1. the correct way is to generate those yourself too
    2. the dangerous way is to ask libxml to add those blanks to your content modifying the content of your document in the process. The result may not be what you expect. There is NO way to guarantee that such a modification won't impact other part of the content of your document. See xmlKeepBlanksDefault () and xmlSaveFormatFile ()
  2. Extra nodes in the document:

    For a XML file as below:

    <?xml version="1.0"?>
<PLAN xmlns="http://www.argus.ca/autotest/1.0/">
<NODE CommFlag="0"/>
<NODE CommFlag="1"/>
</PLAN>

    after parsing it with the function pxmlDoc=xmlParseFile(...);

    I want to the get the content of the first node (node with the CommFlag="0")

    so I did it as following;

    xmlNodePtr pode;
pnode=pxmlDoc->children->children;

    but it does not work. If I change it to

    pnode=pxmlDoc->children->children->next;

    then it works. Can someone explain it to me.

    In XML all characters in the content of the document are significant including blanks and formatting line breaks.

    The extra nodes you are wondering about are just that, text nodes with the formatting spaces wich are part of the document but that people tend to forget. There is a function xmlKeepBlanksDefault () to remove those at parse time, but that's an heuristic, and its use should be limited to case where you are sure there is no mixed-content in the document.

  3. I get compilation errors of existing code like when accessing root or childs fields of nodes

    You are compiling code developed for libxml version 1 and using a libxml2 development environment. Either switch back to libxml v1 devel or even better fix the code to compile with libxml2 (or both) by following the instructions.

  4. I get compilation errors about non existing xmlRootNode or xmlChildrenNode fields

    The source code you are using has been upgraded to be able to compile with both libxml and libxml2, but you need to install a more recent version: libxml(-devel) >= 1.8.8 or libxml2(-devel) >= 2.1.0

  5. XPath implementation looks seriously broken

    XPath implementation prior to 2.3.0 was really incomplete, upgrade to a recent version, the implementation and debug of libxslt generated fixes for most obvious problems.

  6. The example provided in the web page does not compile

    It's hard to maintain the documentation in sync with the code <grin/> ...

    Check the previous points 1/ and 2/ raised before, and send patches.

  7. Where can I get more examples and informations than in the web page

    Ideally a libxml book would be nice. I have no such plan ... But you can:

  8. What about C++ ?

    libxml is written in pure C in order to allow easy reuse on a number of platforms, including embedded systems. I don't intend to convert to C++.

    There is however a C++ wrapper provided by Ari Johnson <ari@btigate.com> which may fullfill your needs:

    Website: http://lusis.org/~ari/xml++/

    Download: http://lusis.org/~ari/xml++/libxml++.tar.gz

  9. How to validate a document a posteriori ?

    It is possible to validate documents which had not been validated at initial parsing time or documents who have been built from scratch using the API. Use the xmlValidateDtd() function. It is also possible to simply add a Dtd to an existing document:

    xmlDocPtr doc; /* your existing document */
        xmlDtdPtr dtd = xmlParseDTD(NULL, filename_of_dtd); /* parse the DTD */
        dtd->name = xmlStrDup((xmlChar*)"root_name"); /* use the given root */

        doc->intSubset = dtd;
        if (doc->children == NULL) xmlAddChild((xmlNodePtr)doc, (xmlNodePtr)dtd);
        else xmlAddPrevSibling(doc->children, (xmlNodePtr)dtd);
  10. etc ...

Daniel Veillard

$Id: FAQ.html,v 1.16 2001/09/13 14:24:44 veillard Exp $