| Table of Contents: - Licensing Terms for libxml
libxml2 is released under the MIT
License; see the file Copyright in the distribution for the precise
wording
- Can I embed libxml2 in a proprietary application ?
Yes. The MIT License allows you to keep proprietary the changes you
made to libxml, but it would be graceful to send-back bug fixes and
improvements as patches for possible incorporation in the main
development tree.
- Do Not Use
libxml1, use libxml2
- Where can I get libxml ?
The original distribution comes from xmlsoft.org or gnome.org
Most Linux and BSD distributions include libxml, this is probably the
safer way for end-users to use libxml.
David Doolin provides precompiled Windows versions at http://www.ce.berkeley.edu/~doolin/code/libxmlwin32/
- I see libxml and libxml2 releases, which one should I install ?
- If you are not constrained by backward compatibility issues with
existing applications, install libxml2 only
- If you are not doing development, you can safely install both.
Usually the packages libxml and libxml2 are
compatible (this is not the case for development packages).
- If you are a developer and your system provides separate packaging
for shared libraries and the development components, it is possible
to install libxml and libxml2, and also libxml-devel
and libxml2-devel
too for libxml2 >= 2.3.0
- If you are developing a new application, please develop against
libxml2(-devel)
- 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. The libxml
packages provided on xmlsoft.org provide
libxml.so.0
- I can't install the libxml(2) RPM package due to failed
dependencies
The most generic solution is to re-fetch 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 packages (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.
- 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 to
update your list of installed shared libs.
- What other libraries are needed to compile/install libxml2 ?
Libxml2 does not require 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 libxml2 will detect and use the
following libs:
- libz : a
highly portable and available widely compression library.
- iconv: a powerful character encoding conversion library. It is
included by default in recent glibc libraries, so it doesn't need to
be installed specifically on Linux. It now seems a part
of the official UNIX specification. Here is one implementation of the
library which source can be found here.
- Make check fails on some platforms
Sometimes 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.
Sometimes (especially on Solaris) make checks fail due to limitations
in make. Try using GNU-make instead.
- I use the CVS version and there is no configure script
The configure script (and other Makefiles) are generated. Use the
autogen.sh script to regenerate the configure script and Makefiles,
like:
./autogen.sh --prefix=/usr --disable-shared
- 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.
- Troubles compiling or linking programs using libxml2
Usually the problem comes from the fact that the compiler doesn't get
the right compilation or linking flags. There is a small shell script
xml2-config which is installed as part of libxml2 usual
install 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 the
Makefile as:
CFLAGS=`xml2-config --cflags`
LIBS=`xml2-config --libs`
- I want to install my own copy of libxml2 in my home directory and
link my programs against it, but it doesn't work
There are many different ways to accomplish this. Here is one way to
do 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 {other
configuration options}
- now run
make followed 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 to
the beginning of your default PATH (so that your own private program
files such as xmllint will be used instead of the normal system
ones). To do this, the Bash command would be
export PATH=/home/user/myxml/xmlinst/bin:$PATH
- Now suppose you have a program
test1.c that you would
like to compile with your "private" library. Simply compile it using
the command
gcc `xml2-config --cflags --libs` -o test test.c
Note that, because your PATH has been set with
/home/user/myxml/xmlinst/bin at the beginning, the xml2-config
program which you just installed will be used instead of the system
default one, and this will automatically get the correct
libraries linked with your program.
- xmlDocDump() generates output on one line.
Libxml2 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:
- the correct way is to generate those yourself too.
- the dangerous way is to ask libxml2 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
affect other parts of the content of your document. See xmlKeepBlanksDefault
() and xmlSaveFormatFile
()
- 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 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 significant
including blanks and formatting line breaks.
The extra nodes you are wondering about are just that, text nodes with
the formatting spaces which 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 cases where you are certain there is no
mixed-content in the document.
- I get compilation errors of existing code like when accessing
root or child 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.
- 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
- XPath implementation looks seriously broken
XPath implementation prior to 2.3.0 was really incomplete. Upgrade to
a recent version, there are no known bugs in the current version.
- 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 send
patches.
- Where can I get more examples and information than provided on the
web page?
Ideally a libxml2 book would be nice. I have no such plan ... But you
can:
- check more deeply the existing
generated doc
- have a look at the set of
examples.
- look for examples of use for libxml2 function using the Gnome code.
For example the following will query the full Gnome CVS base for the
use of the xmlAddChild() function:
http://cvs.gnome.org/lxr/search?string=xmlAddChild
This may be slow, a large hardware donation to the gnome project
could cure this :-)
- Browse
the libxml2 source , I try to write code as clean and documented
as possible, so looking at it may be helpful. In particular the code
of xmllint.c and of the various testXXX.c test programs should
provide good examples of how to do things with the library.
- What about C++ ?
libxml2 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 which may fulfill your needs:
- How to validate a document a posteriori ?
It is possible to validate documents which had not been validated at
initial parsing time or documents which 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);
- 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 before
passing them to the API. This can be accomplished with the iconv library
for instance.
- etc ...
Daniel Veillard |
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