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License(s)

  1. Licensing Terms for libxml

    libxml2 is released under the MITLicense; see the file Copyright in the distribution for the precisewording

  2. Can I embed libxml2 in a proprietary application ?

    Yes. The MIT License allows you to keep proprietary the changes youmade to libxml, but it would be graceful to send-back bug fixes andimprovements as patches for possible incorporation in the maindevelopment tree.

Installation

  1. Do Not Uselibxml1, use libxml2
  2. Where can I get libxml?

    The original distribution comes from xmlsoft.orgor gnome.org

    Most Linux and BSD distributions include libxml, this is probably thesafer way for end-users to use libxml.

    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 ?
    • If you are not constrained by backward compatibility issues withexisting applications, install libxml2 only
    • If you are not doing development, you can safely install both.Usually the packages libxmland libxml2arecompatible (this is not the case for development packages).
    • If you are a developer and your system provides separate packagingfor shared libraries and the development components, it is possibleto install libxml and libxml2, and also libxml-develand libxml2-develtoo for libxml2 >= 2.3.0
    • If you are developing a new application, please develop againstlibxml2(-devel)
  4. I can't install the libxml package, it conflicts with libxml0

    You probably have an old libxml0 package used to provide the sharedlibrary for libxml.so.0, you can probably safely remove it. The libxmlpackages provided on xmlsoft.orgprovidelibxml.so.0

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

    The most generic solution is to re-fetch the latest src.rpm , andrebuild it locally with

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

    If everything goes well it will generate two binary rpm packages (oneproviding the shared libs and xmllint, and the other one, the -develpackage, providing includes, static libraries and scripts needed to buildapplications with libxml(2)) that you can install locally.

Compilation

  1. What is the process to compile libxml2 ?

    As most UNIX libraries libxml2 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 a similar utility toupdate your list of installed shared libs.

  2. What other libraries are needed to compile/install libxml2 ?

    Libxml2 does not require any other library, the normal C ANSI APIshould be sufficient (please report any violation to this rule you mayfind).

    However if found at configuration time libxml2 will detect and use thefollowing libs:

    • libz: ahighly portable and available widely compression library.
    • iconv: a powerful character encoding conversion library. It isincluded by default in recent glibc libraries, so it doesn't need tobe installed specifically on Linux. It now seems a partof the official UNIXspecification. Here is one implementation of thelibrarywhich source can be found here.
  3. Make check fails on some platforms

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

    Sometimes (especially on Solaris) make checks fail due to limitationsin make. Try using GNU-make instead.

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

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

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

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

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

Developercorner

  1. Troubles compiling or linking programs using libxml2

    Usually the problem comes from the fact that the compiler doesn't getthe right compilation or linking flags. There is a small shell scriptxml2-configwhich is installed as part of libxml2 usualinstall process which provides those flags. Use

    xml2-config --cflags

    to get the compilation flags and

    xml2-config --libs

    to get the linker flags. Usually this is done directly from theMakefile as:

    CFLAGS=`xml2-config --cflags`

    LIBS=`xml2-config --libs`

  2. I want to install my own copy of libxml2 in my home directory andlink my programs against it, but it doesn't work

    There are many different ways to accomplish this. Here is one way todo this under Linux. Suppose your home directory is /home/user.Then:

    • Create a subdirectory, let's call it myxml
    • unpack the libxml2 distribution into that subdirectory
    • chdir into the unpacked distribution(/home/user/myxml/libxml2 )
    • configure the library using the "--prefix" switch,specifying an installation subdirectory in/home/user/myxml, e.g.

      ./configure --prefix /home/user/myxml/xmlinst{otherconfiguration options}

    • now run makefollowed by make install
    • At this point, the installation subdirectory contains the complete"private" include files, library files and binary program files (e.g.xmllint), located in

      /home/user/myxml/xmlinst/lib,/home/user/myxml/xmlinst/include and /home/user/myxml/xmlinst/bin

      respectively.
    • In order to use this "private" library, you should first add it tothe beginning of your default PATH (so that your own private programfiles such as xmllint will be used instead of the normal systemones). To do this, the Bash command would be

      export PATH=/home/user/myxml/xmlinst/bin:$PATH

    • Now suppose you have a program test1.cthat you wouldlike to compile with your "private" library. Simply compile it usingthe command

      gcc `xml2-config --cflags --libs` -o test test.c

      Note that, because your PATH has been set with /home/user/myxml/xmlinst/binat the beginning, the xml2-configprogram which you just installed will be used instead of the systemdefault one, and this will automaticallyget the correctlibraries linked with your program.
  3. xmlDocDump() generates output on one line.

    Libxml2 will not inventspaces in the content of adocument since all spaces in the content of a document aresignificant. If you build a tree from the API and wantindentation:

    1. the correct way is to generate those yourself too.
    2. the dangerous way is to ask libxml2 to add those blanks to yourcontent modifying the content of your document in theprocess. The result may not be what you expect. There isNOway to guarantee that such a modification won'taffect other parts of the content of your document. See xmlKeepBlanksDefault()and xmlSaveFormatFile()
  4. 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 functionpxmlDoc=xmlParseFile(...);

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

    so I did it as following;

    xmlNodePtr pnode;
    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 significantincluding blanks and formatting line breaks.

    The extra nodes you are wondering about are just that, text nodes withthe formatting spaces which are part of the document but that people tendto forget. There is a function xmlKeepBlanksDefault()to remove those at parse time, but that's an heuristic, and itsuse should be limited to cases where you are certain there is nomixed-content in the document.

  5. I get compilation errors of existing code like when accessingrootor child fieldsof nodes.

    You are compiling code developed for libxml version 1 and using alibxml2 development environment. Either switch back to libxml v1 devel oreven better fix the code to compile with libxml2 (or both) by following the instructions.

  6. I get compilation errors about non existingxmlRootNodeor xmlChildrenNodefields.

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

  7. XPath implementation looks seriously broken

    XPath implementation prior to 2.3.0 was really incomplete. Upgrade toa recent version, there are no known bugs in the current version.

  8. 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 please sendpatches.

  9. Where can I get more examples and information than provided on theweb page?

    Ideally a libxml2 book would be nice. I have no such plan ... But youcan:

    • check more deeply the existinggenerated doc
    • have a look at the set ofexamples.
    • look for examples of use for libxml2 function using the Gnome code.For example the following will query the full Gnome CVS base for theuse of the xmlAddChild()function:

      http://cvs.gnome.org/lxr/search?string=xmlAddChild

      This may be slow, a large hardware donation to the gnome projectcould cure this :-)

    • Browsethe libxml2 source, I try to write code as clean and documentedas possible, so looking at it may be helpful. In particular the codeof xmllint.c and of the various testXXX.c test programs shouldprovide good examples of how to do things with the library.
  10. What about C++ ?

    libxml2 is written in pure C in order to allow easy reuse on a numberof platforms, including embedded systems. I don't intend to convert toC++.

    There is however a C++ wrapper which may fulfill your needs:

  11. How to validate a document a posteriori ?

    It is possible to validate documents which had not been validated atinitial parsing time or documents which have been built from scratchusing the API. Use the xmlValidateDtd()function. It is also possible to simply add a DTD to an existingdocument:

    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);
              
  12. So what is this funky "xmlChar" used all the time?

    It is a null terminated sequence of utf-8 characters. And only utf-8!You need to convert strings encoded in different ways to utf-8 beforepassing them to the API. This can be accomplished with the iconv libraryfor instance.

  13. etc ...

Daniel Veillard