• Does XML4C support Schema?
• Why XML4C does not support this particular Schema feature?
• Why does my application crash on AIX when I run it under a multi-threaded environment?
• I cannot run the sample applications. What is wrong?
• I just built my own application using the XML4C parser. Why does it crash?
• Is XML4C thread-safe?
• Can't debug into the XML4C DLL with the MSVC debugger
• First-chance exception in Microsoft debugger
• I am seeing memory leaks in XML4C. Are they real?
• Can I validate the data contained in a DOM tree?
• Can I use Xerces to perform write validation
• Why does my multi-threaded application crash on Solaris?
• Why does my application gives unresolved linking errors on Solaris?
• Why do I get Internal Compiler Error when compiling XML4C for a 64bit target with gcc?
• How are entity reference nodes handled in DOM?
• What kinds of URLs are currently supported in XML4C?
• How can I add support for URLs with HTTP/FTP protocols?
• Can I use XML4C to parse HTML?
• I keep getting an error: "invalid UTF-8 character". What's wrong?
• What encodings are supported by Xerces-C / XML4C?
• What character encoding should I use when creating XML documents?
• I find memory leaks in XML4C. How do I eliminate it?
• Is EBCDIC supported?
• How to write out a DOM tree into an XML file?
• Is it OK to call the XMLPlatformUtils::Initialize/Terminate pair of routines multiple times in one program?
• Why does deleting a transcoded string result in assertion on windows?
• How do I transcode to/from something besides the local code page?
• Why DOM_Node::cloneNode() does not clone the pointer assigned to a DOM_Node via DOM_Node::setUserData()?

See the Schema page.

See supported schema features in XML4C 3.5.1

AIX maintains two kinds of libraries on the system, thread-safe and non-thread safe. Multi-threaded libraries on AIX follow a different naming convention, Usually the multi-threaded library names are followed with "_r". For example, libc.a is single threaded whereas libc_r.a is multi-threaded.

To make your multi-threaded application run on AIX, you must ensure that you do not have a "system library path" in your LIBPATH environment variable when you run the application. The appropriate libraries (threaded or non-threaded) are automatically picked up at runtime. An application usually crashes when you build your application for multi-threaded operation but don't point to the thread-safe version of the system libraries. For example, LIBPATH can be simply set as:

	LIBPATH=$HOME/<XML4C>/lib

Where <XML4C> points to the directory where the XML4C application resides.

If, for any reason unrelated to XML4C, you need to keep a "system library path" in your LIBPATH environment variable, you must make sure that you have placed the thread-safe path before you specify the normal system path. For example, you must place /lib/threads before /lib in your LIBPATH variable. That is to say your LIBPATH may look like this:

	export LIBPATH=$HOME/<XML4C>/lib:/usr/lib/threads:/usr/lib

Where /usr/lib is where your system libraries are.

In order to run an application built using XML4C you must set up your path and library search path properly. In the stand-alone version from Apache, you must have the XML4C runtime library available from your path settings. On Windows this library is called xerces-c_1_5.dll which must be available from your PATH settings. (Note that now there are separate debug and release dlls for Windows. If the release dll is named xerces-c_1_5.dll then the debug dll is named xerces-c_1_5d.dll). On UNIX platforms the library is called libxerces-c1_5.so (or .a or .sl) which must be available from your LD_LIBRARY_PATH (or LIBPATH or SHLIB_PATH) environment variable.

Thus, if you installed your binaries under $HOME/fastxmlparser, you need to point your library path to that directory.

	export LIBPATH=$LIBPATH:$HOME/fastxmlparser/lib # (AIX) export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$HOME/fastxmlparser/lib # (Solaris, Linux) export SHLIB_PATH=$SHLIB_PATH:$HOME/fastxmlparser/lib # (HP-UX)

If you are using the enhanced version of this parser from IBM, you will need to put in two additional DLLs. In the Windows build these are icuuc.dll and icudata.dll which must be available from your PATH settings. On UNIX, these libraries are called libicuuc.so and libicudata.so (or .sl for HP-UX or .a for AIX) which must be available from your library search path.

In order to work with the XML4C parser, you have to first initialize the XML subsystem. The most common mistake is to forget this initialization. Before you make any calls to XML4C APIs, you must call:

	XMLPlatformUtils::Initialize(): try { XMLPlatformUtils::Initialize(); } catch (const XMLException& toCatch) { // Do your failure processing here }

This initializes the XML4C system and sets its internal variables. Note that you must the include util/PlatformUtils.hpp file for this to work.

This is not a question that has a simple yes/no answer. Here are the rules for using XML4C in a multi-threaded environment:

Within an address space, an instance of the parser may be used without restriction from a single thread, or an instance of the parser can be accessed from multiple threads, provided the application guarantees that only one thread has entered a method of the parser at any one time.

When two or more parser instances exist in a process, the instances can be used concurrently, without external synchronization. That is, in an application containing two parsers and two threads, one parser can be running within the first thread concurrently with the second parser running within the second thread.

The same rules apply to XML4C DOM documents. Multiple document instances may be concurrently accessed from different threads, but any given document instance can only be accessed by one thread at a time.

DOMStrings allow multiple concurrent readers. All DOMString const methods are thread safe, and can be concurrently entered by multiple threads. Non-const DOMString methods, such as appendData(), are not thread safe and the application must guarantee that no other methods (including const methods) are executed concurrently with them.

Unless you have the .pdb files, all you are getting with the debug library is that it uses the debug heap manager, so that you can compile your stuff in debug mode and not be dangerous. If you want full symbolic info for the XML4C library, you'll need the .pdb files, and to get those, you'll need to rebuild the XML4C library.

XML4C uses C++ exceptions internally, as part of its normal operation. By default, the MSVC debugger will stop on each of these with the "First-chance exception ..." message.

To stop this from happening do this:

• start debugging (so the debug menu appears)
• from the debug menu select "Exceptions"
• from the box that opens select "Microsoft C++ Exception" and set it to "Stop if not handled" instead of "stop always".

You'll still land in the debugger if your program is terminating abnormally, but it will be at your problem, not from the internal XML4C exceptions.

The XML4C library allocates and caches some commonly reused items. The storage for these may be reported as memory leaks by some heap analysis tools; to avoid the problem, call the function XMLPlatformUtils::Terminate() before your application exits. This will free all memory that was being held by the library.

For most applications, the use of Terminate() is optional. The system will recover all memory when the application process shuts down. The exception to this is the use of XML4C from DLLs that will be repeatedly loaded and unloaded from within the same process. To avoid memory leaks with this kind of use, Terminate() must be called before unloading the XML4C library

No. This is a frequently requested feature, but at this time it is not possible to feed XML data from the DOM directly back to the DTD validator. The best option for now is to generate XML source from the DOM and feed that back into the parser.

The answers are: "No" and "No." Write Validation is a commonly requested feature, but XML4C does not have it yet.

The best you can do for now is to create the DOM document, write it back as XML and re-parse it.

The problem appears because the throw call on Solaris 2.6 is not multi-thread safe. Sun Microsystems provides a patch to solve this problem. To get the latest patch for solving this problem, go to SunSolve.sun.com and get the appropriate patch for your operating system. For Intel machines running Solaris, you need to get Patch ID 104678. For SPARC machines you need to get Patch ID #105591.

On Solaris there are a few things that need to be done before you execute your application using XML4C. In case you're using the binary build of XML4C make sure that the OS and compiler are the same version as the ones used to build the binary. Different OS and compiler versions might cause unresolved linking problems or compilation errors. If the versions are different, rebuild the XML4C library on your system before building your application. If you're using ICU (which is packaged with XML4C) you need to rebuild the compatible version of ICU first.

Also check that the library path is set properly and that the correct versions of gmake and autoconf are on your system.

This is a compiler problem. Try turning off optimization to bypass the problem.

If you are using the native DOM classes, the function setExpandEntityReferences controls how entities appear in the DOM tree. When setExpandEntityReferences is set to false (the default), an occurrence of an entity reference in the XML document will be represented by a subtree with an EntityReference node at the root whose children represent the entity expansion. Entity expansion will be a DOM tree representing the structure of the entity expansion, not a text node containing the entity expansion as text.

If setExpandEntityReferences is true, an entity reference in the XML document is represented by only the nodes that represent the entity expansion. The DOM tree will not contain any entityReference nodes.

The XMLURL class provides for limited URL support. It understands the file://, http://, and ftp:// URL types, and is capable or parsing them into their constituent components, and normalizing them. It also supports the commonly required action of conglomerating a base and relative URL into a single URL. In other words, it performs the limited set of functions required by an XML parser.

Another thing that URLs commonly do are to create an input stream that provides access to the entity referenced. The parser, as shipped, only supports this functionality on URLs in the form file:/// and file://localhost/, i.e. only when the URL refers to a local file.

You may enable support for HTTP and FTP URLs by implementing and installing a NetAccessor object. When a NetAccessor object is installed, the URL class will use it to create input streams for the remote entities referred to by such URLs.

Support for the http: protocol is now included by default on all platforms.

To address the need to make remote connections to resources specified using additional protocols, ftp for example, XML4C provides the NetAccessor interface. The header file is src/util/XMLNetAccessor.hpp. This interface allows you to plug in your own implementation of URL networking code into the XML4C parser.

Yes, but only if the HTML follows the rules given in the XML specification. Most HTML, however, does not follow the XML rules, and will generate XML well-formedness errors.

Most commonly, the XML encoding = declaration is either incorrect or missing. Without a declaration, XML defaults to the use utf-8 character encoding, which is not compatible with the default text file encoding on most systems.

The XML declaration should look something like this:

<?xml version="1.0" encoding="iso-8859-1"?>

Make sure to specify the encoding that is actually used by file. The encoding for "plain" text files depends both on the operating system and the locale (country and language) in use.

Another common source of problems is that some characters are not allowed in XML documents, according to the XML spec. Typical disallowed characters are control characters, even if you escape them using the Character Reference form. See the XML spec, sections 2.2 and 4.1 for details. If the parser is generating an Invalid character (Unicode: 0x???) error, it is very likely that there's a character in there that you can't see. You can generally use a UNIX command like "od -hc" to find it.

Xerces-C has intrinsic support for ASCII, UTF-8, UTF-16 (Big/Small Endian), UCS4 (Big/Small Endian), EBCDIC code pages IBM037 and IBM1140 encodings, ISO-8859-1 (aka Latin1) and Windows-1252. This means that it can parse input XML files in these above mentioned encodings.

XML4C -- the version of Xerces-C available from IBM -- extends this set to include the encodings listed in the table below.

Some implementations or ports of Xerces-C provide support for additional encodings. The exact set will depend on the supplier of the parser and on the character set transcoding services in use.

The best choice in most cases is either utf-8 or utf-16. Advantages of these encodings include:

• The best portability. These encodings are more widely supported by XML processors than any others, meaning that your documents will have the best possible chance of being read correctly, no matter where they end up.
• Full international character support. Both utf-8 and utf-16 cover the full Unicode character set, which includes all of the characters from all major national, international and industry character sets.
• Efficient. utf-8 has the smaller storage requirements for documents that are primarily composed of of characters from the Latin alphabet. utf-16 is more efficient for encoding Asian languages. But both encodings cover all languages without loss.

The only drawback of utf-8 or utf-16 is that they are not the native text file format for most systems, meaning that common text file editors and viewers can not be directly used.

A second choice of encoding would be any of the others listed in the table above. This works best when the xml encoding is the same as the default system encoding on the machine where the XML document is being prepared, because the document will then display correctly as a plain text file. For UNIX systems in countries speaking Western European languages, the encoding will usually be iso-8859-1.

The versions of Xerces distributed by IBM, both C and Java (known respectively as XML4C and XML4J), include all of the encodings listed in the above table, on all platforms.

A word of caution for Windows users: The default character set on Windows systems is windows-1252, not iso-8859-1. While XML4C does recognize this Windows encoding, it is a poor choice for portable XML data because it is not widely recognized by other XML processing tools. If you are using a Windows-based editing tool to generate XML, check which character set it generates, and make sure that the resulting XML specifies the correct name in the encoding="..." declaration.

The "leaks" that are reported through a leak-detector or heap-analysis tools aren't really leaks in most application, in that the memory usage does not grow over time as the XML parser is used and re-used.

What you are seeing as leaks are actually lazily evaluated data allocated into static variables. This data gets released when the application ends. You can make a call to XMLPlatformUtil::terminate() to release all the lazily allocated variables before you exit your program.

Yes, XML4C supports EBCDIC. When creating EBCDIC encoded XML data, the preferred encoding is ibm1140. Also supported is ibm037 (and its alternate name, ebcdic-cp-us); this encoding is almost the same as ibm1140, but it lacks the Euro symbol.

These two encodings, ibm1140 and ibm037, are available on both Xerces-C and IBM XML4C, on all platforms.

On IBM System 390, XML4C also supports two alternative forms, ibm037-s390 and ibm1140-s390. These are similar to the base ibm037 and ibm1140 encodings, but with alternate mappings of the EBCDIC new-line character, which allows them to appear as normal text files on System 390s. These encodings are not supported on other platforms, and should not be used for portable data.

XML4C on System 390 and AS/400 also provides additional EBCDIC encodings, including those for the character sets of different countries. The exact set supported will be platform dependent, and these encodings are not recommended for portable XML data.

This feature is not yet availabe in the parser. Take a look at the DOMPrint sample for an example on parsing XML file, then writing it out back to the screen. You can use that code.

No. XMLPlatformUtils::Initialize() can only be called once per process. Call Initialize() when you start and Terminate() when you end.

Both your application program and the Xerces DLL must use the same *DLL* version of the runtime library. If either statically links to the runtime library, the problem will still occur. For example, for a Win32/VC6 build, the runtime library build setting MUST be "Multithreaded DLL" for release builds and "Debug Multithreaded DLL" for debug builds.

XMLString::transcode() will transcode from XMLCh to the local code page, and other APIs which take a char* assume that the source text is in the local code page. If this is not true, you must transcode the text yourself. You can do this using local transcoding support on your OS, such as Iconv on Unix or or IBM's ICU package. However, if your transcoding needs are simple, you can achieve some better portability by using the Xerces parser's transcoder wrappers. You get a transcoder like this:

• 1. Call XMLPlatformUtils::fgTransServer->MakeNewTranscoderFor() and provide the name of the encoding you wish to create a transcoder for. This will return a transcoder to you, which you own and must delete when you are through with it. NOTE: You must provide a maximum block size that you will pass to the transcoder at one time, and you must blocks of characters of this count or smaller when you do your transcoding. The reason for this is that this is really an internal API and is used by the parser itself to do transcoding. The parser always does transcoding in known block sizes, and this allows transcoders to be much more efficient for internal use since it knows the max size it will ever have to deal with and can set itself up for that internally. In general, you should stick to block sizes in the 4 to 64K range.
• 2. The returned transcoder is something derived from XMLTranscoder, so they are all returned to you via that interface.
• 3. This object is really just a wrapper around the underlying transcoding system actually in use by your version of Xerces, and does whatever is necessary to handle differences between the XMLCh representation and the representation uesd by that underying transocding system.
• 4. The transcoder object has two primary APIs, transcodeFrom() and transcodeTo(). These transcode between the XMLCh format and the encoding you indicated.
• 5. These APIs will transcode as much of the source data as will fit into the outgoing buffer you provide. They will tell you how much of the source they ate and how much of the target they filled. You can use this information to continue the process until all source is consumed.
• 6. char* data is always dealt with in terms of bytes, and XMLCh data is always dealt with in terms of characters. Don't mix up which you are dealing with or you will not get the correct results, since many encodings don't have a one to one relationship of characters to bytes.
• 7. When transcoding from XMLCh to the target encoding, the transcodeTo() method provides an 'unrepresentable flag' parameter, which tells the transcoder how to deal with an XMLCh code point that cannot be converted legally to the target encoding, which can easily happen since XMLCh is Unicode and can represent thousands of code points. The options are to use a default replacement character (which the underlying transcoding service will choose, and which is guaranteed to be legal for the target encoding), or to throw an exception.

There are several possible options for how cloneNode should handle userData:

• 1) Copy the pointer. May be a Very Bad Idea if you really wanted the data associated with a particular node object.
• 2) Clone the object being pointed at. Maybe a Very Bad Idea if that object, in turn, wasn't designed to be cloned at this time.
• 3) A complex call-back API has been proposed which would allow the userData object to tell the DOM which of these three options should be taken, but that would require that only objects implementing that API be registered as userData. That doesn't seem to be a good option.
• 4) Do nothing. This is by far the lowest-overhead and safest choice. And since cloneNode is a DOM operation, and userData is _not_ defined by the standard DOM API, one can make a very strong case for this being the "most correct" option.

We chose (4), very deliberately. If you want one of the others, you can implement it by creating your own wrapper operation for cloneNode() and calling that.

NOTE that userData should be considered a nonportable, experimental feature of the Xerces DOM. It may evaporate entirely in favor of a scheme based on the DOM Level 3 "node key" mechanism, when that becomes officially available.