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<title>Expat XML Parser</title>
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<td class="banner"><h1>The Expat XML Parser</h1></td>
<td class="releaseno">Release 2.0.1</td>
<div class="content">
<p>Expat is a library, written in C, for parsing XML documents. It's
the underlying XML parser for the open source Mozilla project, Perl's
<code>XML::Parser</code>, Python's <code>xml.parsers.expat</code>, and
other open-source XML parsers.</p>
<p>This library is the creation of James Clark, who's also given us
groff (an nroff look-alike), Jade (an implemention of ISO's DSSSL
stylesheet language for SGML), XP (a Java XML parser package), XT (a
Java XSL engine). James was also the technical lead on the XML
Working Group at W3C that produced the XML specification.</p>
<p>This is free software, licensed under the <a
href="../COPYING">MIT/X Consortium license</a>. You may download it
from <a href="">the Expat home page</a>.
<p>The bulk of this document was originally commissioned as an article
by <a href=""></a>. They graciously allowed
Clark Cooper to retain copyright and to distribute it with Expat.
This version has been substantially extended to include documentation
on features which have been added since the original article was
published, and additional information on using the original
<hr />
<h2>Table of Contents</h2>
<li><a href="#overview">Overview</a></li>
<li><a href="#building">Building and Installing</a></li>
<li><a href="#using">Using Expat</a></li>
<li><a href="#reference">Reference</a>
<li><a href="#creation">Parser Creation Functions</a>
<li><a href="#XML_ParserCreate">XML_ParserCreate</a></li>
<li><a href="#XML_ParserCreateNS">XML_ParserCreateNS</a></li>
<li><a href="#XML_ParserCreate_MM">XML_ParserCreate_MM</a></li>
<li><a href="#XML_ExternalEntityParserCreate">XML_ExternalEntityParserCreate</a></li>
<li><a href="#XML_ParserFree">XML_ParserFree</a></li>
<li><a href="#XML_ParserReset">XML_ParserReset</a></li>
<li><a href="#parsing">Parsing Functions</a>
<li><a href="#XML_Parse">XML_Parse</a></li>
<li><a href="#XML_ParseBuffer">XML_ParseBuffer</a></li>
<li><a href="#XML_GetBuffer">XML_GetBuffer</a></li>
<li><a href="#XML_StopParser">XML_StopParser</a></li>
<li><a href="#XML_ResumeParser">XML_ResumeParser</a></li>
<li><a href="#XML_GetParsingStatus">XML_GetParsingStatus</a></li>
<li><a href="#setting">Handler Setting Functions</a>
<li><a href="#XML_SetStartElementHandler">XML_SetStartElementHandler</a></li>
<li><a href="#XML_SetEndElementHandler">XML_SetEndElementHandler</a></li>
<li><a href="#XML_SetElementHandler">XML_SetElementHandler</a></li>
<li><a href="#XML_SetCharacterDataHandler">XML_SetCharacterDataHandler</a></li>
<li><a href="#XML_SetProcessingInstructionHandler">XML_SetProcessingInstructionHandler</a></li>
<li><a href="#XML_SetCommentHandler">XML_SetCommentHandler</a></li>
<li><a href="#XML_SetStartCdataSectionHandler">XML_SetStartCdataSectionHandler</a></li>
<li><a href="#XML_SetEndCdataSectionHandler">XML_SetEndCdataSectionHandler</a></li>
<li><a href="#XML_SetCdataSectionHandler">XML_SetCdataSectionHandler</a></li>
<li><a href="#XML_SetDefaultHandler">XML_SetDefaultHandler</a></li>
<li><a href="#XML_SetDefaultHandlerExpand">XML_SetDefaultHandlerExpand</a></li>
<li><a href="#XML_SetExternalEntityRefHandler">XML_SetExternalEntityRefHandler</a></li>
<li><a href="#XML_SetExternalEntityRefHandlerArg">XML_SetExternalEntityRefHandlerArg</a></li>
<li><a href="#XML_SetSkippedEntityHandler">XML_SetSkippedEntityHandler</a></li>
<li><a href="#XML_SetUnknownEncodingHandler">XML_SetUnknownEncodingHandler</a></li>
<li><a href="#XML_SetStartNamespaceDeclHandler">XML_SetStartNamespaceDeclHandler</a></li>
<li><a href="#XML_SetEndNamespaceDeclHandler">XML_SetEndNamespaceDeclHandler</a></li>
<li><a href="#XML_SetNamespaceDeclHandler">XML_SetNamespaceDeclHandler</a></li>
<li><a href="#XML_SetXmlDeclHandler">XML_SetXmlDeclHandler</a></li>
<li><a href="#XML_SetStartDoctypeDeclHandler">XML_SetStartDoctypeDeclHandler</a></li>
<li><a href="#XML_SetEndDoctypeDeclHandler">XML_SetEndDoctypeDeclHandler</a></li>
<li><a href="#XML_SetDoctypeDeclHandler">XML_SetDoctypeDeclHandler</a></li>
<li><a href="#XML_SetElementDeclHandler">XML_SetElementDeclHandler</a></li>
<li><a href="#XML_SetAttlistDeclHandler">XML_SetAttlistDeclHandler</a></li>
<li><a href="#XML_SetEntityDeclHandler">XML_SetEntityDeclHandler</a></li>
<li><a href="#XML_SetUnparsedEntityDeclHandler">XML_SetUnparsedEntityDeclHandler</a></li>
<li><a href="#XML_SetNotationDeclHandler">XML_SetNotationDeclHandler</a></li>
<li><a href="#XML_SetNotStandaloneHandler">XML_SetNotStandaloneHandler</a></li>
<li><a href="#position">Parse Position and Error Reporting Functions</a>
<li><a href="#XML_GetErrorCode">XML_GetErrorCode</a></li>
<li><a href="#XML_ErrorString">XML_ErrorString</a></li>
<li><a href="#XML_GetCurrentByteIndex">XML_GetCurrentByteIndex</a></li>
<li><a href="#XML_GetCurrentLineNumber">XML_GetCurrentLineNumber</a></li>
<li><a href="#XML_GetCurrentColumnNumber">XML_GetCurrentColumnNumber</a></li>
<li><a href="#XML_GetCurrentByteCount">XML_GetCurrentByteCount</a></li>
<li><a href="#XML_GetInputContext">XML_GetInputContext</a></li>
<li><a href="#miscellaneous">Miscellaneous Functions</a>
<li><a href="#XML_SetUserData">XML_SetUserData</a></li>
<li><a href="#XML_GetUserData">XML_GetUserData</a></li>
<li><a href="#XML_UseParserAsHandlerArg">XML_UseParserAsHandlerArg</a></li>
<li><a href="#XML_SetBase">XML_SetBase</a></li>
<li><a href="#XML_GetBase">XML_GetBase</a></li>
<li><a href="#XML_GetSpecifiedAttributeCount">XML_GetSpecifiedAttributeCount</a></li>
<li><a href="#XML_GetIdAttributeIndex">XML_GetIdAttributeIndex</a></li>
<li><a href="#XML_SetEncoding">XML_SetEncoding</a></li>
<li><a href="#XML_SetParamEntityParsing">XML_SetParamEntityParsing</a></li>
<li><a href="#XML_UseForeignDTD">XML_UseForeignDTD</a></li>
<li><a href="#XML_SetReturnNSTriplet">XML_SetReturnNSTriplet</a></li>
<li><a href="#XML_DefaultCurrent">XML_DefaultCurrent</a></li>
<li><a href="#XML_ExpatVersion">XML_ExpatVersion</a></li>
<li><a href="#XML_ExpatVersionInfo">XML_ExpatVersionInfo</a></li>
<li><a href="#XML_GetFeatureList">XML_GetFeatureList</a></li>
<li><a href="#XML_FreeContentModel">XML_FreeContentModel</a></li>
<li><a href="#XML_MemMalloc">XML_MemMalloc</a></li>
<li><a href="#XML_MemRealloc">XML_MemRealloc</a></li>
<li><a href="#XML_MemFree">XML_MemFree</a></li>
<hr />
<h2><a name="overview">Overview</a></h2>
<p>Expat is a stream-oriented parser. You register callback (or
handler) functions with the parser and then start feeding it the
document. As the parser recognizes parts of the document, it will
call the appropriate handler for that part (if you've registered one.)
The document is fed to the parser in pieces, so you can start parsing
before you have all the document. This also allows you to parse really
huge documents that won't fit into memory.</p>
<p>Expat can be intimidating due to the many kinds of handlers and
options you can set. But you only need to learn four functions in
order to do 90% of what you'll want to do with it:</p>
<dt><code><a href= "#XML_ParserCreate"
<dd>Create a new parser object.</dd>
<dt><code><a href= "#XML_SetElementHandler"
<dd>Set handlers for start and end tags.</dd>
<dt><code><a href= "#XML_SetCharacterDataHandler"
<dd>Set handler for text.</dd>
<dt><code><a href= "#XML_Parse"
<dd>Pass a buffer full of document to the parser</dd>
<p>These functions and others are described in the <a
href="#reference">reference</a> part of this document. The reference
section also describes in detail the parameters passed to the
different types of handlers.</p>
<p>Let's look at a very simple example program that only uses 3 of the
above functions (it doesn't need to set a character handler.) The
program <a href="../examples/outline.c">outline.c</a> prints an
element outline, indenting child elements to distinguish them from the
parent element that contains them. The start handler does all the
work. It prints two indenting spaces for every level of ancestor
elements, then it prints the element and attribute
information. Finally it increments the global <code>Depth</code>
<pre class="eg">
int Depth;
start(void *data, const char *el, const char **attr) {
int i;
for (i = 0; i &lt; Depth; i++)
printf(" ");
printf("%s", el);
for (i = 0; attr[i]; i += 2) {
printf(" %s='%s'", attr[i], attr[i + 1]);
} /* End of start handler */
<p>The end tag simply does the bookkeeping work of decrementing
<pre class="eg">
end(void *data, const char *el) {
} /* End of end handler */
<p>Note the <code>XMLCALL</code> annotation used for the callbacks.
This is used to ensure that the Expat and the callbacks are using the
same calling convention in case the compiler options used for Expat
itself and the client code are different. Expat tries not to care
what the default calling convention is, though it may require that it
be compiled with a default convention of "cdecl" on some platforms.
For code which uses Expat, however, the calling convention is
specified by the <code>XMLCALL</code> annotation on most platforms;
callbacks should be defined using this annotation.</p>
<p>The <code>XMLCALL</code> annotation was added in Expat 1.95.7, but
existing working Expat applications don't need to add it (since they
are already using the "cdecl" calling convention, or they wouldn't be
working). The annotation is only needed if the default calling
convention may be something other than "cdecl". To use the annotation
safely with older versions of Expat, you can conditionally define it
<em>after</em> including Expat's header file:</p>
<pre class="eg">
#include &lt;expat.h&gt;
#ifndef XMLCALL
#if defined(_MSC_EXTENSIONS) &amp;&amp; !defined(__BEOS__) &amp;&amp; !defined(__CYGWIN__)
#define XMLCALL __cdecl
#elif defined(__GNUC__)
#define XMLCALL __attribute__((cdecl))
#define XMLCALL
<p>After creating the parser, the main program just has the job of
shoveling the document to the parser so that it can do its work.</p>
<hr />
<h2><a name="building">Building and Installing Expat</a></h2>
<p>The Expat distribution comes as a compressed (with GNU gzip) tar
file. You may download the latest version from <a href=
"" >Source Forge</a>. After
unpacking this, cd into the directory. Then follow either the Win32
directions or Unix directions below.</p>
<h3>Building under Win32</h3>
<p>If you're using the GNU compiler under cygwin, follow the Unix
directions in the next section. Otherwise if you have Microsoft's
Developer Studio installed, then from Windows Explorer double-click on
"expat.dsp" in the lib directory and build and install in the usual
<p>Alternatively, you may download the Win32 binary package that
contains the "expat.h" include file and a pre-built DLL.</p>
<h3>Building under Unix (or GNU)</h3>
<p>First you'll need to run the configure shell script in order to
configure the Makefiles and headers for your system.</p>
<p>If you're happy with all the defaults that configure picks for you,
and you have permission on your system to install into /usr/local, you
can install Expat with this sequence of commands:</p>
<pre class="eg">
make install
<p>There are some options that you can provide to this script, but the
only one we'll mention here is the <code>--prefix</code> option. You
can find out all the options available by running configure with just
the <code>--help</code> option.</p>
<p>By default, the configure script sets things up so that the library
gets installed in <code>/usr/local/lib</code> and the associated
header file in <code>/usr/local/include</code>. But if you were to
give the option, <code>--prefix=/home/me/mystuff</code>, then the
library and header would get installed in
<code>/home/me/mystuff/lib</code> and
<code>/home/me/mystuff/include</code> respectively.</p>
<h3>Configuring Expat Using the Pre-Processor</h3>
<p>Expat's feature set can be configured using a small number of
pre-processor definitions. The definition of this symbols does not
affect the set of entry points for Expat, only the behavior of the API
and the definition of character types in the case of
<code>XML_UNICODE_WCHAR_T</code>. The symbols are:</p>
<dl class="cpp-symbols">
<dd>Include support for using and reporting DTD-based content. If
this is defined, default attribute values from an external DTD subset
are reported and attribute value normalization occurs based on the
type of attributes defined in the external subset. Without
this, Expat has a smaller memory footprint and can be faster, but will
not load external entities or process conditional sections. This does
not affect the set of functions available in the API.</dd>
<dd>When defined, support for the <cite><a href=
"" >Namespaces in XML</a></cite>
specification is included.</dd>
<dd>When defined, character data reported to the application is
encoded in UTF-16 using wide characters of the type
<code>XML_Char</code>. This is implied if
<code>XML_UNICODE_WCHAR_T</code> is defined.</dd>
<dd>If defined, causes the <code>XML_Char</code> character type to be
defined using the <code>wchar_t</code> type; otherwise, <code>unsigned
short</code> is used. Defining this implies
<dd>If defined, causes the <code>XML_Size</code> and <code>XML_Index</code>
integer types to be at least 64 bits in size. This is intended to support
processing of very large input streams, where the return values of
<code><a href="#XML_GetCurrentByteIndex" >XML_GetCurrentByteIndex</a></code>,
<code><a href="#XML_GetCurrentLineNumber" >XML_GetCurrentLineNumber</a></code> and
<code><a href="#XML_GetCurrentColumnNumber" >XML_GetCurrentColumnNumber</a></code>
could overflow. It may not be supported by all compilers, and is turned
off by default.</dd>
<dd>The number of input bytes of markup context which the parser will
ensure are available for reporting via <code><a href=
"#XML_GetInputContext" >XML_GetInputContext</a></code>. This is
normally set to 1024, and must be set to a positive interger. If this
is not defined, the input context will not be available and <code><a
href= "#XML_GetInputContext" >XML_GetInputContext</a></code> will
always report NULL. Without this, Expat has a smaller memory
footprint and can be faster.</dd>
<dd>On Windows, this should be set if Expat is going to be linked
statically with the code that calls it; this is required to get all
the right MSVC magic annotations correct. This is ignored on other
<hr />
<h2><a name="using">Using Expat</a></h2>
<h3>Compiling and Linking Against Expat</h3>
<p>Unless you installed Expat in a location not expected by your
compiler and linker, all you have to do to use Expat in your programs
is to include the Expat header (<code>#include &lt;expat.h&gt;</code>)
in your files that make calls to it and to tell the linker that it
needs to link against the Expat library. On Unix systems, this would
usually be done with the <code>-lexpat</code> argument. Otherwise,
you'll need to tell the compiler where to look for the Expat header
and the linker where to find the Expat library. You may also need to
take steps to tell the operating system where to find this library at
run time.</p>
<p>On a Unix-based system, here's what a Makefile might look like when
Expat is installed in a standard location:</p>
<pre class="eg">
LIBS= -lexpat
xmlapp: xmlapp.o
$(CC) $(LDFLAGS) -o xmlapp xmlapp.o $(LIBS)
<p>If you installed Expat in, say, <code>/home/me/mystuff</code>, then
the Makefile would look like this:</p>
<pre class="eg">
CFLAGS= -I/home/me/mystuff/include
LIBS= -L/home/me/mystuff/lib -lexpat
xmlapp: xmlapp.o
$(CC) $(LDFLAGS) -o xmlapp xmlapp.o $(LIBS)
<p>You'd also have to set the environment variable
<code>LD_LIBRARY_PATH</code> to <code>/home/me/mystuff/lib</code> (or
to <code>${LD_LIBRARY_PATH}:/home/me/mystuff/lib</code> if
LD_LIBRARY_PATH already has some directories in it) in order to run
your application.</p>
<h3>Expat Basics</h3>
<p>As we saw in the example in the overview, the first step in parsing
an XML document with Expat is to create a parser object. There are <a
href="#creation">three functions</a> in the Expat API for creating a
parser object. However, only two of these (<code><a href=
"#XML_ParserCreate" >XML_ParserCreate</a></code> and <code><a href=
"#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>) can be used for
constructing a parser for a top-level document. The object returned
by these functions is an opaque pointer (i.e. "expat.h" declares it as
void *) to data with further internal structure. In order to free the
memory associated with this object you must call <code><a href=
"#XML_ParserFree" >XML_ParserFree</a></code>. Note that if you have
provided any <a href="#userdata">user data</a> that gets stored in the
parser, then your application is responsible for freeing it prior to
calling <code>XML_ParserFree</code>.</p>
<p>The objects returned by the parser creation functions are good for
parsing only one XML document or external parsed entity. If your
application needs to parse many XML documents, then it needs to create
a parser object for each one. The best way to deal with this is to
create a higher level object that contains all the default
initialization you want for your parser objects.</p>
<p>Walking through a document hierarchy with a stream oriented parser
will require a good stack mechanism in order to keep track of current
context. For instance, to answer the simple question, "What element
does this text belong to?" requires a stack, since the parser may have
descended into other elements that are children of the current one and
has encountered this text on the way out.</p>
<p>The things you're likely to want to keep on a stack are the
currently opened element and it's attributes. You push this
information onto the stack in the start handler and you pop it off in
the end handler.</p>
<p>For some tasks, it is sufficient to just keep information on what
the depth of the stack is (or would be if you had one.) The outline
program shown above presents one example. Another such task would be
skipping over a complete element. When you see the start tag for the
element you want to skip, you set a skip flag and record the depth at
which the element started. When the end tag handler encounters the
same depth, the skipped element has ended and the flag may be
cleared. If you follow the convention that the root element starts at
1, then you can use the same variable for skip flag and skip
<pre class="eg">
init_info(Parseinfo *info) {
info->skip = 0;
info->depth = 1;
/* Other initializations here */
} /* End of init_info */
rawstart(void *data, const char *el, const char **attr) {
Parseinfo *inf = (Parseinfo *) data;
if (! inf->skip) {
if (should_skip(inf, el, attr)) {
inf->skip = inf->depth;
start(inf, el, attr); /* This does rest of start handling */
} /* End of rawstart */
rawend(void *data, const char *el) {
Parseinfo *inf = (Parseinfo *) data;
if (! inf->skip)
end(inf, el); /* This does rest of end handling */
if (inf->skip == inf->depth)
inf->skip = 0;
} /* End rawend */
<p>Notice in the above example the difference in how depth is
manipulated in the start and end handlers. The end tag handler should
be the mirror image of the start tag handler. This is necessary to
properly model containment. Since, in the start tag handler, we
incremented depth <em>after</em> the main body of start tag code, then
in the end handler, we need to manipulate it <em>before</em> the main
body. If we'd decided to increment it first thing in the start
handler, then we'd have had to decrement it last thing in the end
<h3 id="userdata">Communicating between handlers</h3>
<p>In order to be able to pass information between different handlers
without using globals, you'll need to define a data structure to hold
the shared variables. You can then tell Expat (with the <code><a href=
"#XML_SetUserData" >XML_SetUserData</a></code> function) to pass a
pointer to this structure to the handlers. This is the first
argument received by most handlers. In the <a href="#reference"
>reference section</a>, an argument to a callback function is named
<code>userData</code> and have type <code>void *</code> if the user
data is passed; it will have the type <code>XML_Parser</code> if the
parser itself is passed. When the parser is passed, the user data may
be retrieved using <code><a href="#XML_GetUserData"
<p>One common case where multiple calls to a single handler may need
to communicate using an application data structure is the case when
content passed to the character data handler (set by <code><a href=
>XML_SetCharacterDataHandler</a></code>) needs to be accumulated. A
common first-time mistake with any of the event-oriented interfaces to
an XML parser is to expect all the text contained in an element to be
reported by a single call to the character data handler. Expat, like
many other XML parsers, reports such data as a sequence of calls;
there's no way to know when the end of the sequence is reached until a
different callback is made. A buffer referenced by the user data
structure proves both an effective and convenient place to accumulate
character data.</p>
<!-- XXX example needed here -->
<h3>XML Version</h3>
<p>Expat is an XML 1.0 parser, and as such never complains based on
the value of the <code>version</code> pseudo-attribute in the XML
declaration, if present.</p>
<p>If an application needs to check the version number (to support
alternate processing), it should use the <code><a href=
"#XML_SetXmlDeclHandler" >XML_SetXmlDeclHandler</a></code> function to
set a handler that uses the information in the XML declaration to
determine what to do. This example shows how to check that only a
version number of <code>"1.0"</code> is accepted:</p>
<pre class="eg">
static int wrong_version;
static XML_Parser parser;
static void XMLCALL
xmldecl_handler(void *userData,
const XML_Char *version,
const XML_Char *encoding,
int standalone)
static const XML_Char Version_1_0[] = {'1', '.', '0', 0};
int i;
for (i = 0; i &lt; (sizeof(Version_1_0) / sizeof(Version_1_0[0])); ++i) {
if (version[i] != Version_1_0[i]) {
wrong_version = 1;
/* also clear all other handlers: */
XML_SetCharacterDataHandler(parser, NULL);
<h3>Namespace Processing</h3>
<p>When the parser is created using the <code><a href=
"#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>, function, Expat
performs namespace processing. Under namespace processing, Expat
consumes <code>xmlns</code> and <code>xmlns:...</code> attributes,
which declare namespaces for the scope of the element in which they
occur. This means that your start handler will not see these
attributes. Your application can still be informed of these
declarations by setting namespace declaration handlers with <a href=
<p>Element type and attribute names that belong to a given namespace
are passed to the appropriate handler in expanded form. By default
this expanded form is a concatenation of the namespace URI, the
separator character (which is the 2nd argument to <code><a href=
"#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>), and the local
name (i.e. the part after the colon). Names with undeclared prefixes
are not well-formed when namespace processing is enabled, and will
trigger an error. Unprefixed attribute names are never expanded,
and unprefixed element names are only expanded when they are in the
scope of a default namespace.</p>
<p>However if <code><a href= "#XML_SetReturnNSTriplet"
>XML_SetReturnNSTriplet</a></code> has been called with a non-zero
<code>do_nst</code> parameter, then the expanded form for names with
an explicit prefix is a concatenation of: URI, separator, local name,
separator, prefix.</p>
<p>You can set handlers for the start of a namespace declaration and
for the end of a scope of a declaration with the <code><a href=
"#XML_SetNamespaceDeclHandler" >XML_SetNamespaceDeclHandler</a></code>
function. The StartNamespaceDeclHandler is called prior to the start
tag handler and the EndNamespaceDeclHandler is called after the
corresponding end tag that ends the namespace's scope. The namespace
start handler gets passed the prefix and URI for the namespace. For a
default namespace declaration (xmlns='...'), the prefix will be null.
The URI will be null for the case where the default namespace is being
unset. The namespace end handler just gets the prefix for the closing
<p>These handlers are called for each declaration. So if, for
instance, a start tag had three namespace declarations, then the
StartNamespaceDeclHandler would be called three times before the start
tag handler is called, once for each declaration.</p>
<h3>Character Encodings</h3>
<p>While XML is based on Unicode, and every XML processor is required
to recognized UTF-8 and UTF-16 (1 and 2 byte encodings of Unicode),
other encodings may be declared in XML documents or entities. For the
main document, an XML declaration may contain an encoding
&lt;?xml version="1.0" encoding="ISO-8859-2"?&gt;
<p>External parsed entities may begin with a text declaration, which
looks like an XML declaration with just an encoding declaration:</p>
&lt;?xml encoding="Big5"?&gt;
<p>With Expat, you may also specify an encoding at the time of
creating a parser. This is useful when the encoding information may
come from a source outside the document itself (like a higher level
<p><a name="builtin_encodings"></a>There are four built-in encodings
in Expat:</p>
<p>Anything else discovered in an encoding declaration or in the
protocol encoding specified in the parser constructor, triggers a call
to the <code>UnknownEncodingHandler</code>. This handler gets passed
the encoding name and a pointer to an <code>XML_Encoding</code> data
structure. Your handler must fill in this structure and return
<code>XML_STATUS_OK</code> if it knows how to deal with the
encoding. Otherwise the handler should return
<code>XML_STATUS_ERROR</code>. The handler also gets passed a pointer
to an optional application data structure that you may indicate when
you set the handler.</p>
<p>Expat places restrictions on character encodings that it can
support by filling in the <code>XML_Encoding</code> structure.
include file:</p>
<li>Every ASCII character that can appear in a well-formed XML document
must be represented by a single byte, and that byte must correspond to
it's ASCII encoding (except for the characters $@\^'{}~)</li>
<li>Characters must be encoded in 4 bytes or less.</li>
<li>All characters encoded must have Unicode scalar values less than or
equal to 65535 (0xFFFF)<em>This does not apply to the built-in support
for UTF-16 and UTF-8</em></li>
<li>No character may be encoded by more that one distinct sequence of
<p><code>XML_Encoding</code> contains an array of integers that
correspond to the 1st byte of an encoding sequence. If the value in
the array for a byte is zero or positive, then the byte is a single
byte encoding that encodes the Unicode scalar value contained in the
array. A -1 in this array indicates a malformed byte. If the value is
-2, -3, or -4, then the byte is the beginning of a 2, 3, or 4 byte
sequence respectively. Multi-byte sequences are sent to the convert
function pointed at in the <code>XML_Encoding</code> structure. This
function should return the Unicode scalar value for the sequence or -1
if the sequence is malformed.</p>
<p>One pitfall that novice Expat users are likely to fall into is that
although Expat may accept input in various encodings, the strings that
it passes to the handlers are always encoded in UTF-8 or UTF-16
(depending on how Expat was compiled). Your application is responsible
for any translation of these strings into other encodings.</p>
<h3>Handling External Entity References</h3>
<p>Expat does not read or parse external entities directly. Note that
any external DTD is a special case of an external entity. If you've
set no <code>ExternalEntityRefHandler</code>, then external entity
references are silently ignored. Otherwise, it calls your handler with
the information needed to read and parse the external entity.</p>
<p>Your handler isn't actually responsible for parsing the entity, but
it is responsible for creating a subsidiary parser with <code><a href=
>XML_ExternalEntityParserCreate</a></code> that will do the job. This
returns an instance of <code>XML_Parser</code> that has handlers and
other data structures initialized from the parent parser. You may then
use <code><a href= "#XML_Parse" >XML_Parse</a></code> or <code><a
href= "#XML_ParseBuffer">XML_ParseBuffer</a></code> calls against this
parser. Since external entities my refer to other external entities,
your handler should be prepared to be called recursively.</p>
<h3>Parsing DTDs</h3>
<p>In order to parse parameter entities, before starting the parse,
you must call <code><a href= "#XML_SetParamEntityParsing"
>XML_SetParamEntityParsing</a></code> with one of the following
<dd>Don't parse parameter entities or the external subset</dd>
<dd>Parse parameter entites and the external subset unless
<code>standalone</code> was set to "yes" in the XML declaration.</dd>
<dd>Always parse parameter entities and the external subset</dd>
<p>In order to read an external DTD, you also have to set an external
entity reference handler as described above.</p>
<h3 id="stop-resume">Temporarily Stopping Parsing</h3>
<p>Expat 1.95.8 introduces a new feature: its now possible to stop
parsing temporarily from within a handler function, even if more data
has already been passed into the parser. Applications for this
<li>Supporting the <a href= ""
>XInclude</a> specification.</li>
<li>Delaying further processing until additional information is
available from some other source.</li>
<li>Adjusting processor load as task priorities shift within an
<li>Stopping parsing completely (simply free or reset the parser
instead of resuming in the outer parsing loop). This can be useful
if a application-domain error is found in the XML being parsed or if
the result of the parse is determined not to be useful after
<p>To take advantage of this feature, the main parsing loop of an
application needs to support this specifically. It cannot be
supported with a parsing loop compatible with Expat 1.95.7 or
earlier (though existing loops will continue to work without
supporting the stop/resume feature).</p>
<p>An application that uses this feature for a single parser will have
the rough structure (in pseudo-code):</p>
<pre class="pseudocode">
fd = open_input()
p = create_parser()
if parse_xml(p, fd) {
/* suspended */
int suspended = 1;
while (suspended) {
if ready_to_resume() {
suspended = continue_parsing(p, fd);
<p>An application that may resume any of several parsers based on
input (either from the XML being parsed or some other source) will
certainly have more interesting control structures.</p>
<p>This C function could be used for the <code>parse_xml</code>
function mentioned in the pseudo-code above:</p>
<pre class="eg">
#define BUFF_SIZE 10240
/* Parse a document from the open file descriptor 'fd' until the parse
is complete (the document has been completely parsed, or there's
been an error), or the parse is stopped. Return non-zero when
the parse is merely suspended.
parse_xml(XML_Parser p, int fd)
for (;;) {
int last_chunk;
int bytes_read;
enum XML_Status status;
void *buff = XML_GetBuffer(p, BUFF_SIZE);
if (buff == NULL) {
/* handle error... */
return 0;
bytes_read = read(fd, buff, BUFF_SIZE);
if (bytes_read &lt; 0) {
/* handle error... */
return 0;
status = XML_ParseBuffer(p, bytes_read, bytes_read == 0);
switch (status) {
/* handle error... */
return 0;
return 1;
if (bytes_read == 0)
return 0;
<p>The corresponding <code>continue_parsing</code> function is
somewhat simpler, since it only need deal with the return code from
<code><a href= "#XML_ResumeParser">XML_ResumeParser</a></code>; it can
delegate the input handling to the <code>parse_xml</code>
<pre class="eg">
/* Continue parsing a document which had been suspended. The 'p' and
'fd' arguments are the same as passed to parse_xml(). Return
non-zero when the parse is suspended.
continue_parsing(XML_Parser p, int fd)
enum XML_Status status = XML_ResumeParser(p);
switch (status) {
/* handle error... */
return 0;
/* handle error... */
return 0;.
return 1;
return parse_xml(p, fd);
<p>Now that we've seen what a mess the top-level parsing loop can
become, what have we gained? Very simply, we can now use the <code><a
href= "#XML_StopParser" >XML_StopParser</a></code> function to stop
parsing, without having to go to great lengths to avoid additional
processing that we're expecting to ignore. As a bonus, we get to stop
parsing <em>temporarily</em>, and come back to it when we're
<p>To stop parsing from a handler function, use the <code><a href=
"#XML_StopParser" >XML_StopParser</a></code> function. This function
takes two arguments; the parser being stopped and a flag indicating
whether the parse can be resumed in the future.</p>
<!-- XXX really need more here -->
<hr />
<!-- ================================================================ -->
<h2><a name="reference">Expat Reference</a></h2>
<h3><a name="creation">Parser Creation</a></h3>
<pre class="fcndec" id="XML_ParserCreate">
XML_ParserCreate(const XML_Char *encoding);
<div class="fcndef">
Construct a new parser. If encoding is non-null, it specifies a
character encoding to use for the document. This overrides the document
encoding declaration. There are four built-in encodings:
Any other value will invoke a call to the UnknownEncodingHandler.
<pre class="fcndec" id="XML_ParserCreateNS">
XML_ParserCreateNS(const XML_Char *encoding,
XML_Char sep);
<div class="fcndef">
Constructs a new parser that has namespace processing in effect. Namespace
expanded element names and attribute names are returned as a concatenation
of the namespace URI, <em>sep</em>, and the local part of the name. This
means that you should pick a character for <em>sep</em> that can't be
part of a legal URI. There is a special case when <em>sep</em> is the null
character <code>'\0'</code>: the namespace URI and the local part will be
concatenated without any separator - this is intended to support RDF processors.
It is a programming error to use the null separator with
<a href= "#XML_SetReturnNSTriplet">namespace triplets</a>.</div>
<pre class="fcndec" id="XML_ParserCreate_MM">
XML_ParserCreate_MM(const XML_Char *encoding,
const XML_Memory_Handling_Suite *ms,
const XML_Char *sep);
<pre class="signature">
typedef struct {
void *(XMLCALL *malloc_fcn)(size_t size);
void *(XMLCALL *realloc_fcn)(void *ptr, size_t size);
void (XMLCALL *free_fcn)(void *ptr);
} XML_Memory_Handling_Suite;
<div class="fcndef">
<p>Construct a new parser using the suite of memory handling functions
specified in <code>ms</code>. If <code>ms</code> is NULL, then use the
standard set of memory management functions. If <code>sep</code> is
non NULL, then namespace processing is enabled in the created parser
and the character pointed at by sep is used as the separator between
the namespace URI and the local part of the name.</p>
<pre class="fcndec" id="XML_ExternalEntityParserCreate">
XML_ExternalEntityParserCreate(XML_Parser p,
const XML_Char *context,
const XML_Char *encoding);
<div class="fcndef">
Construct a new <code>XML_Parser</code> object for parsing an external
general entity. Context is the context argument passed in a call to a
ExternalEntityRefHandler. Other state information such as handlers,
user data, namespace processing is inherited from the parser passed as
the 1st argument. So you shouldn't need to call any of the behavior
changing functions on this parser (unless you want it to act
differently than the parent parser).
<pre class="fcndec" id="XML_ParserFree">
XML_ParserFree(XML_Parser p);
<div class="fcndef">
Free memory used by the parser. Your application is responsible for
freeing any memory associated with <a href="#userdata">user data</a>.
<pre class="fcndec" id="XML_ParserReset">
XML_ParserReset(XML_Parser p,
const XML_Char *encoding);
<div class="fcndef">
Clean up the memory structures maintained by the parser so that it may
be used again. After this has been called, <code>parser</code> is
ready to start parsing a new document. All handlers are cleared from
the parser, except for the unknownEncodingHandler. The parser's external
state is re-initialized except for the values of ns and ns_triplets.
This function may not be used on a parser created using <code><a href=
"#XML_ExternalEntityParserCreate" >XML_ExternalEntityParserCreate</a
></code>; it will return <code>XML_FALSE</code> in that case. Returns
<code>XML_TRUE</code> on success. Your application is responsible for
dealing with any memory associated with <a href="#userdata">user data</a>.
<h3><a name="parsing">Parsing</a></h3>
<p>To state the obvious: the three parsing functions <code><a href=
"#XML_Parse" >XML_Parse</a></code>, <code><a href= "#XML_ParseBuffer">
XML_ParseBuffer</a></code> and <code><a href= "#XML_GetBuffer">
XML_GetBuffer</a></code> must not be called from within a handler
unless they operate on a separate parser instance, that is, one that
did not call the handler. For example, it is OK to call the parsing
functions from within an <code>XML_ExternalEntityRefHandler</code>,
if they apply to the parser created by
<code><a href= "#XML_ExternalEntityParserCreate"
<p>Note: the <code>len</code> argument passed to these functions
should be considerably less than the maximum value for an integer,
as it could create an integer overflow situation if the added
lengths of a buffer and the unprocessed portion of the previous buffer
exceed the maximum integer value. Input data at the end of a buffer
will remain unprocessed if it is part of an XML token for which the
end is not part of that buffer.</p>
<pre class="fcndec" id="XML_Parse">
enum XML_Status XMLCALL
XML_Parse(XML_Parser p,
const char *s,
int len,
int isFinal);
<pre class="signature">
enum XML_Status {
<div class="fcndef">
Parse some more of the document. The string <code>s</code> is a buffer
containing part (or perhaps all) of the document. The number of bytes of s
that are part of the document is indicated by <code>len</code>. This means
that <code>s</code> doesn't have to be null terminated. It also means that
if <code>len</code> is larger than the number of bytes in the block of
memory that <code>s</code> points at, then a memory fault is likely. The
<code>isFinal</code> parameter informs the parser that this is the last
piece of the document. Frequently, the last piece is empty (i.e.
<code>len</code> is zero.)
If a parse error occurred, it returns <code>XML_STATUS_ERROR</code>.
Otherwise it returns <code>XML_STATUS_OK</code> value.
<pre class="fcndec" id="XML_ParseBuffer">
enum XML_Status XMLCALL
XML_ParseBuffer(XML_Parser p,
int len,
int isFinal);
<div class="fcndef">
This is just like <code><a href= "#XML_Parse" >XML_Parse</a></code>,
except in this case Expat provides the buffer. By obtaining the
buffer from Expat with the <code><a href= "#XML_GetBuffer"
>XML_GetBuffer</a></code> function, the application can avoid double
copying of the input.
<pre class="fcndec" id="XML_GetBuffer">
void * XMLCALL
XML_GetBuffer(XML_Parser p,
int len);
<div class="fcndef">
Obtain a buffer of size <code>len</code> to read a piece of the document
into. A NULL value is returned if Expat can't allocate enough memory for
this buffer. This has to be called prior to every call to
<code><a href= "#XML_ParseBuffer" >XML_ParseBuffer</a></code>. A
typical use would look like this:
<pre class="eg">
for (;;) {
int bytes_read;
void *buff = XML_GetBuffer(p, BUFF_SIZE);
if (buff == NULL) {
/* handle error */
bytes_read = read(docfd, buff, BUFF_SIZE);
if (bytes_read &lt; 0) {
/* handle error */
if (! XML_ParseBuffer(p, bytes_read, bytes_read == 0)) {
/* handle parse error */
if (bytes_read == 0)
<pre class="fcndec" id="XML_StopParser">
enum XML_Status XMLCALL
XML_StopParser(XML_Parser p,
XML_Bool resumable);
<div class="fcndef">
<p>Stops parsing, causing <code><a href= "#XML_Parse"
>XML_Parse</a></code> or <code><a href= "#XML_ParseBuffer"
>XML_ParseBuffer</a></code> to return. Must be called from within a
call-back handler, except when aborting (when <code>resumable</code>
is <code>XML_FALSE</code>) an already suspended parser. Some
call-backs may still follow because they would otherwise get
lost, including
<li> the end element handler for empty elements when stopped in the
start element handler,</li>
<li> the end namespace declaration handler when stopped in the end
element handler,</li>
<li> the character data handler when stopped in the character data handler
while making multiple call-backs on a contiguous chunk of characters,</li>
and possibly others.</p>
<p>This can be called from most handlers, including DTD related
call-backs, except when parsing an external parameter entity and
<code>resumable</code> is <code>XML_TRUE</code>. Returns
<code>XML_STATUS_OK</code> when successful,
<code>XML_STATUS_ERROR</code> otherwise. The possible error codes
<dd>when suspending an already suspended parser.</dd>
<dd>when the parser has already finished.</dd>
<dd>when suspending while parsing an external PE.</dd>
<p>Since the stop/resume feature requires application support in the
outer parsing loop, it is an error to call this function for a parser
not being handled appropriately; see <a href= "#stop-resume"
>Temporarily Stopping Parsing</a> for more information.</p>
<p>When <code>resumable</code> is <code>XML_TRUE</code> then parsing
is <em>suspended</em>, that is, <code><a href= "#XML_Parse"
>XML_Parse</a></code> and <code><a href= "#XML_ParseBuffer"
>XML_ParseBuffer</a></code> return <code>XML_STATUS_SUSPENDED</code>.
Otherwise, parsing is <em>aborted</em>, that is, <code><a href=
"#XML_Parse" >XML_Parse</a></code> and <code><a href=
"#XML_ParseBuffer" >XML_ParseBuffer</a></code> return
<code>XML_STATUS_ERROR</code> with error code
This will be applied to the current parser instance only, that is, if
there is a parent parser then it will continue parsing when the
external entity reference handler returns. It is up to the
implementation of that handler to call <code><a href=
"#XML_StopParser" >XML_StopParser</a></code> on the parent parser
(recursively), if one wants to stop parsing altogether.</p>
<p>When suspended, parsing can be resumed by calling <code><a href=
"#XML_ResumeParser" >XML_ResumeParser</a></code>.</p>
<p>New in Expat 1.95.8.</p>
<pre class="fcndec" id="XML_ResumeParser">
enum XML_Status XMLCALL
XML_ResumeParser(XML_Parser p);
<div class="fcndef">
<p>Resumes parsing after it has been suspended with <code><a href=
"#XML_StopParser" >XML_StopParser</a></code>. Must not be called from
within a handler call-back. Returns same status codes as <code><a
href= "#XML_Parse">XML_Parse</a></code> or <code><a href=
"#XML_ParseBuffer" >XML_ParseBuffer</a></code>. An additional error
code, <code>XML_ERROR_NOT_SUSPENDED</code>, will be returned if the
parser was not currently suspended.</p>
This must be called on the most deeply nested child parser instance
first, and on its parent parser only after the child parser has
finished, to be applied recursively until the document entity's parser
is restarted. That is, the parent parser will not resume by itself
and it is up to the application to call <code><a href=
"#XML_ResumeParser" >XML_ResumeParser</a></code> on it at the
appropriate moment.</p>
<p>New in Expat 1.95.8.</p>
<pre class="fcndec" id="XML_GetParsingStatus">
XML_GetParsingStatus(XML_Parser p,
XML_ParsingStatus *status);
<pre class="signature">
enum XML_Parsing {
typedef struct {
enum XML_Parsing parsing;
XML_Bool finalBuffer;
} XML_ParsingStatus;
<div class="fcndef">
<p>Returns status of parser with respect to being initialized,
parsing, finished, or suspended, and whether the final buffer is being
processed. The <code>status</code> parameter <em>must not</em> be
<p>New in Expat 1.95.8.</p>
<h3><a name="setting">Handler Setting</a></h3>
<p>Although handlers are typically set prior to parsing and left alone, an
application may choose to set or change the handler for a parsing event
while the parse is in progress. For instance, your application may choose
to ignore all text not descended from a <code>para</code> element. One
way it could do this is to set the character handler when a para start tag
is seen, and unset it for the corresponding end tag.</p>
<p>A handler may be <em>unset</em> by providing a NULL pointer to the
appropriate handler setter. None of the handler setting functions have
a return value.</p>
<p>Your handlers will be receiving strings in arrays of type
<code>XML_Char</code>. This type is conditionally defined in expat.h as
either <code>char</code>, <code>wchar_t</code> or <code>unsigned short</code>.
The former implies UTF-8 encoding, the latter two imply UTF-16 encoding.
Note that you'll receive them in this form independent of the original
encoding of the document.</p>
<div class="handler">
<pre class="setter" id="XML_SetStartElementHandler">
XML_SetStartElementHandler(XML_Parser p,
XML_StartElementHandler start);
<pre class="signature">
typedef void
(XMLCALL *XML_StartElementHandler)(void *userData,
const XML_Char *name,
const XML_Char **atts);
<p>Set handler for start (and empty) tags. Attributes are passed to the start
handler as a pointer to a vector of char pointers. Each attribute seen in
a start (or empty) tag occupies 2 consecutive places in this vector: the
attribute name followed by the attribute value. These pairs are terminated
by a null pointer.</p>
<p>Note that an empty tag generates a call to both start and end handlers
(in that order).</p>
<div class="handler">
<pre class="setter" id="XML_SetEndElementHandler">
XML_SetEndElementHandler(XML_Parser p,
<pre class="signature">
typedef void
(XMLCALL *XML_EndElementHandler)(void *userData,
const XML_Char *name);
<p>Set handler for end (and empty) tags. As noted above, an empty tag
generates a call to both start and end handlers.</p>
<div class="handler">
<pre class="setter" id="XML_SetElementHandler">
XML_SetElementHandler(XML_Parser p,
XML_StartElementHandler start,
XML_EndElementHandler end);
<p>Set handlers for start and end tags with one call.</p>
<div class="handler">
<pre class="setter" id="XML_SetCharacterDataHandler">
XML_SetCharacterDataHandler(XML_Parser p,
XML_CharacterDataHandler charhndl)
<pre class="signature">
typedef void
(XMLCALL *XML_CharacterDataHandler)(void *userData,
const XML_Char *s,
int len);
<p>Set a text handler. The string your handler receives
is <em>NOT nul-terminated</em>. You have to use the length argument
to deal with the end of the string. A single block of contiguous text
free of markup may still result in a sequence of calls to this handler.
In other words, if you're searching for a pattern in the text, it may
be split across calls to this handler. Note: Setting this handler to NULL
may <em>NOT immediately</em> terminate call-backs if the parser is currently
processing such a single block of contiguous markup-free text, as the parser
will continue calling back until the end of the block is reached.</p>
<div class="handler">
<pre class="setter" id="XML_SetProcessingInstructionHandler">
XML_SetProcessingInstructionHandler(XML_Parser p,
XML_ProcessingInstructionHandler proc)
<pre class="signature">
typedef void
(XMLCALL *XML_ProcessingInstructionHandler)(void *userData,
const XML_Char *target,
const XML_Char *data);
<p>Set a handler for processing instructions. The target is the first word
in the processing instruction. The data is the rest of the characters in
it after skipping all whitespace after the initial word.</p>
<div class="handler">
<pre class="setter" id="XML_SetCommentHandler">
XML_SetCommentHandler(XML_Parser p,
XML_CommentHandler cmnt)
<pre class="signature">
typedef void
(XMLCALL *XML_CommentHandler)(void *userData,
const XML_Char *data);
<p>Set a handler for comments. The data is all text inside the comment
<div class="handler">
<pre class="setter" id="XML_SetStartCdataSectionHandler">
XML_SetStartCdataSectionHandler(XML_Parser p,
XML_StartCdataSectionHandler start);
<pre class="signature">
typedef void
(XMLCALL *XML_StartCdataSectionHandler)(void *userData);
<p>Set a handler that gets called at the beginning of a CDATA section.</p>
<div class="handler">
<pre class="setter" id="XML_SetEndCdataSectionHandler">
XML_SetEndCdataSectionHandler(XML_Parser p,
XML_EndCdataSectionHandler end);
<pre class="signature">
typedef void
(XMLCALL *XML_EndCdataSectionHandler)(void *userData);
<p>Set a handler that gets called at the end of a CDATA section.</p>
<div class="handler">
<pre class="setter" id="XML_SetCdataSectionHandler">
XML_SetCdataSectionHandler(XML_Parser p,
XML_StartCdataSectionHandler start,
XML_EndCdataSectionHandler end)
<p>Sets both CDATA section handlers with one call.</p>
<div class="handler">
<pre class="setter" id="XML_SetDefaultHandler">
XML_SetDefaultHandler(XML_Parser p,
XML_DefaultHandler hndl)
<pre class="signature">
typedef void
(XMLCALL *XML_DefaultHandler)(void *userData,
const XML_Char *s,
int len);
<p>Sets a handler for any characters in the document which wouldn't
otherwise be handled. This includes both data for which no handlers
can be set (like some kinds of DTD declarations) and data which could
be reported but which currently has no handler set. The characters
are passed exactly as they were present in the XML document except
that they will be encoded in UTF-8 or UTF-16. Line boundaries are not
normalized. Note that a byte order mark character is not passed to the
default handler. There are no guarantees about how characters are
divided between calls to the default handler: for example, a comment
might be split between multiple calls. Setting the handler with
this call has the side effect of turning off expansion of references
to internally defined general entities. Instead these references are
passed to the default handler.</p>
<p>See also <code><a
<div class="handler">
<pre class="setter" id="XML_SetDefaultHandlerExpand">
XML_SetDefaultHandlerExpand(XML_Parser p,
XML_DefaultHandler hndl)
<pre class="signature">
typedef void
(XMLCALL *XML_DefaultHandler)(void *userData,
const XML_Char *s,
int len);
<p>This sets a default handler, but doesn't inhibit the expansion of
internal entity references. The entity reference will not be passed
to the default handler.</p>
<p>See also <code><a
<div class="handler">
<pre class="setter" id="XML_SetExternalEntityRefHandler">
XML_SetExternalEntityRefHandler(XML_Parser p,
XML_ExternalEntityRefHandler hndl)
<pre class="signature">
typedef int
(XMLCALL *XML_ExternalEntityRefHandler)(XML_Parser p,
const XML_Char *context,
const XML_Char *base,
const XML_Char *systemId,
const XML_Char *publicId);
<p>Set an external entity reference handler. This handler is also
called for processing an external DTD subset if parameter entity parsing
is in effect. (See <a href="#XML_SetParamEntityParsing">
<p>The <code>context</code> parameter specifies the parsing context in
the format expected by the <code>context</code> argument to <code><a
>XML_ExternalEntityParserCreate</a></code>. <code>code</code> is
valid only until the handler returns, so if the referenced entity is
to be parsed later, it must be copied. <code>context</code> is NULL
only when the entity is a parameter entity, which is how one can
differentiate between general and parameter entities.</p>
<p>The <code>base</code> parameter is the base to use for relative
system identifiers. It is set by <code><a
href="#XML_SetBase">XML_SetBase</a></code> and may be NULL. The
<code>publicId</code> parameter is the public id given in the entity
declaration and may be NULL. <code>systemId</code> is the system
identifier specified in the entity declaration and is never NULL.</p>
<p>There are a couple of ways in which this handler differs from
others. First, this handler returns a status indicator (an
integer). <code>XML_STATUS_OK</code> should be returned for successful
handling of the external entity reference. Returning
<code>XML_STATUS_ERROR</code> indicates failure, and causes the
calling parser to return an
<p>Second, instead of having the user data as its first argument, it
receives the parser that encountered the entity reference. This, along
with the context parameter, may be used as arguments to a call to
<code><a href= "#XML_ExternalEntityParserCreate"
>XML_ExternalEntityParserCreate</a></code>. Using the returned
parser, the body of the external entity can be recursively parsed.</p>
<p>Since this handler may be called recursively, it should not be saving
information into global or static variables.</p>
<pre class="fcndec" id="XML_SetExternalEntityRefHandlerArg">
XML_SetExternalEntityRefHandlerArg(XML_Parser p,
void *arg)
<div class="fcndef">
<p>Set the argument passed to the ExternalEntityRefHandler. If
<code>arg</code> is not NULL, it is the new value passed to the
handler set using <code><a href="#XML_SetExternalEntityRefHandler"
>XML_SetExternalEntityRefHandler</a></code>; if <code>arg</code> is
NULL, the argument passed to the handler function will be the parser
object itself.</p>
The type of <code>arg</code> and the type of the first argument to the
ExternalEntityRefHandler do not match. This function takes a
<code>void *</code> to be passed to the handler, while the handler
accepts an <code>XML_Parser</code>. This is a historical accident,
but will not be corrected before Expat 2.0 (at the earliest) to avoid
causing compiler warnings for code that's known to work with this
API. It is the responsibility of the application code to know the
actual type of the argument passed to the handler and to manage it
<div class="handler">
<pre class="setter" id="XML_SetSkippedEntityHandler">
XML_SetSkippedEntityHandler(XML_Parser p,
XML_SkippedEntityHandler handler)
<pre class="signature">
typedef void
(XMLCALL *XML_SkippedEntityHandler)(void *userData,
const XML_Char *entityName,
int is_parameter_entity);
<p>Set a skipped entity handler. This is called in two situations:</p>
<li>An entity reference is encountered for which no declaration
has been read <em>and</em> this is not an error.</li>
<li>An internal entity reference is read, but not expanded, because
<a href="#XML_SetDefaultHandler"><code>XML_SetDefaultHandler</code></a>
has been called.</li>
<p>The <code>is_parameter_entity</code> argument will be non-zero for
a parameter entity and zero for a general entity.</p> <p>Note: skipped
parameter entities in declarations and skipped general entities in
attribute values cannot be reported, because the event would be out of
sync with the reporting of the declarations or attribute values</p>
<div class="handler">
<pre class="setter" id="XML_SetUnknownEncodingHandler">
XML_SetUnknownEncodingHandler(XML_Parser p,
XML_UnknownEncodingHandler enchandler,
void *encodingHandlerData)
<pre class="signature">
typedef int
(XMLCALL *XML_UnknownEncodingHandler)(void *encodingHandlerData,
const XML_Char *name,
XML_Encoding *info);
typedef struct {
int map[256];
void *data;
int (XMLCALL *convert)(void *data, const char *s);
void (XMLCALL *release)(void *data);
} XML_Encoding;
<p>Set a handler to deal with encodings other than the <a
href="#builtin_encodings">built in set</a>. This should be done before
<code><a href= "#XML_Parse" >XML_Parse</a></code> or <code><a href=
"#XML_ParseBuffer" >XML_ParseBuffer</a></code> have been called on the
given parser.</p> <p>If the handler knows how to deal with an encoding
with the given name, it should fill in the <code>info</code> data
structure and return <code>XML_STATUS_OK</code>. Otherwise it
should return <code>XML_STATUS_ERROR</code>. The handler will be called
at most once per parsed (external) entity. The optional application
data pointer <code>encodingHandlerData</code> will be passed back to
the handler.</p>
<p>The map array contains information for every possible possible leading
byte in a byte sequence. If the corresponding value is &gt;= 0, then it's
a single byte sequence and the byte encodes that Unicode value. If the
value is -1, then that byte is invalid as the initial byte in a sequence.
If the value is -n, where n is an integer &gt; 1, then n is the number of
bytes in the sequence and the actual conversion is accomplished by a
call to the function pointed at by convert. This function may return -1
if the sequence itself is invalid. The convert pointer may be null if
there are only single byte codes. The data parameter passed to the convert
function is the data pointer from <code>XML_Encoding</code>. The
string s is <em>NOT</em> nul-terminated and points at the sequence of
bytes to be converted.</p>
<p>The function pointed at by <code>release</code> is called by the
parser when it is finished with the encoding. It may be NULL.</p>
<div class="handler">
<pre class="setter" id="XML_SetStartNamespaceDeclHandler">
XML_SetStartNamespaceDeclHandler(XML_Parser p,
XML_StartNamespaceDeclHandler start);
<pre class="signature">
typedef void
(XMLCALL *XML_StartNamespaceDeclHandler)(void *userData,
const XML_Char *prefix,
const XML_Char *uri);
<p>Set a handler to be called when a namespace is declared. Namespace
declarations occur inside start tags. But the namespace declaration start
handler is called before the start tag handler for each namespace declared
in that start tag.</p>
<div class="handler">
<pre class="setter" id="XML_SetEndNamespaceDeclHandler">
XML_SetEndNamespaceDeclHandler(XML_Parser p,
XML_EndNamespaceDeclHandler end);
<pre class="signature">
typedef void
(XMLCALL *XML_EndNamespaceDeclHandler)(void *userData,
const XML_Char *prefix);
<p>Set a handler to be called when leaving the scope of a namespace
declaration. This will be called, for each namespace declaration,
after the handler for the end tag of the element in which the
namespace was declared.</p>
<div class="handler">
<pre class="setter" id="XML_SetNamespaceDeclHandler">
XML_SetNamespaceDeclHandler(XML_Parser p,
XML_StartNamespaceDeclHandler start,
XML_EndNamespaceDeclHandler end)
<p>Sets both namespace declaration handlers with a single call.</p>
<div class="handler">
<pre class="setter" id="XML_SetXmlDeclHandler">
XML_SetXmlDeclHandler(XML_Parser p,
XML_XmlDeclHandler xmldecl);
<pre class="signature">
typedef void
(XMLCALL *XML_XmlDeclHandler)(void *userData,
const XML_Char *version,
const XML_Char *encoding,
int standalone);
<p>Sets a handler that is called for XML declarations and also for
text declarations discovered in external entities. The way to
distinguish is that the <code>version</code> parameter will be NULL
for text declarations. The <code>encoding</code> parameter may be NULL
for an XML declaration. The <code>standalone</code> argument will
contain -1, 0, or 1 indicating respectively that there was no
standalone parameter in the declaration, that it was given as no, or
that it was given as yes.</p>
<div class="handler">
<pre class="setter" id="XML_SetStartDoctypeDeclHandler">
XML_SetStartDoctypeDeclHandler(XML_Parser p,
XML_StartDoctypeDeclHandler start);
<pre class="signature">
typedef void
(XMLCALL *XML_StartDoctypeDeclHandler)(void *userData,
const XML_Char *doctypeName,
const XML_Char *sysid,
const XML_Char *pubid,
int has_internal_subset);
<p>Set a handler that is called at the start of a DOCTYPE declaration,
before any external or internal subset is parsed. Both <code>sysid</code>
and <code>pubid</code> may be NULL. The <code>has_internal_subset</code>
will be non-zero if the DOCTYPE declaration has an internal subset.</p>
<div class="handler">
<pre class="setter" id="XML_SetEndDoctypeDeclHandler">
XML_SetEndDoctypeDeclHandler(XML_Parser p,
XML_EndDoctypeDeclHandler end);
<pre class="signature">
typedef void
(XMLCALL *XML_EndDoctypeDeclHandler)(void *userData);
<p>Set a handler that is called at the end of a DOCTYPE declaration,
after parsing any external subset.</p>
<div class="handler">
<pre class="setter" id="XML_SetDoctypeDeclHandler">
XML_SetDoctypeDeclHandler(XML_Parser p,
XML_StartDoctypeDeclHandler start,
XML_EndDoctypeDeclHandler end);
<p>Set both doctype handlers with one call.</p>
<div class="handler">
<pre class="setter" id="XML_SetElementDeclHandler">
XML_SetElementDeclHandler(XML_Parser p,
XML_ElementDeclHandler eldecl);
<pre class="signature">
typedef void
(XMLCALL *XML_ElementDeclHandler)(void *userData,
const XML_Char *name,
XML_Content *model);
<pre class="signature">
enum XML_Content_Type {
enum XML_Content_Quant {
typedef struct XML_cp XML_Content;
struct XML_cp {
enum XML_Content_Type type;
enum XML_Content_Quant quant;
const XML_Char * name;
unsigned int numchildren;
XML_Content * children;
<p>Sets a handler for element declarations in a DTD. The handler gets
called with the name of the element in the declaration and a pointer
to a structure that contains the element model. It is the
application's responsibility to free this data structure using
<code><a href="#XML_FreeContentModel"
<p>The <code>model</code> argument is the root of a tree of
<code>XML_Content</code> nodes. If <code>type</code> equals
<code>XML_CTYPE_EMPTY</code> or <code>XML_CTYPE_ANY</code>, then
<code>quant</code> will be <code>XML_CQUANT_NONE</code>, and the other
fields will be zero or NULL. If <code>type</code> is
<code>XML_CTYPE_MIXED</code>, then <code>quant</code> will be
<code>XML_CQUANT_NONE</code> or <code>XML_CQUANT_REP</code> and
<code>numchildren</code> will contain the number of elements that are
allowed to be mixed in and <code>children</code> points to an array of
<code>XML_Content</code> structures that will all have type
XML_CTYPE_NAME with no quantification. Only the root node can be type
<code>XML_CTYPE_EMPTY</code>, <code>XML_CTYPE_ANY</code>, or
<p>For type <code>XML_CTYPE_NAME</code>, the <code>name</code> field
points to the name and the <code>numchildren</code> and
<code>children</code> fields will be zero and NULL. The
<code>quant</code> field will indicate any quantifiers placed on the
<p>Types <code>XML_CTYPE_CHOICE</code> and <code>XML_CTYPE_SEQ</code>
indicate a choice or sequence respectively. The
<code>numchildren</code> field indicates how many nodes in the choice
or sequence and <code>children</code> points to the nodes.</p>
<div class="handler">
<pre class="setter" id="XML_SetAttlistDeclHandler">
XML_SetAttlistDeclHandler(XML_Parser p,
XML_AttlistDeclHandler attdecl);
<pre class="signature">
typedef void
(XMLCALL *XML_AttlistDeclHandler)(void *userData,
const XML_Char *elname,
const XML_Char *attname,
const XML_Char *att_type,
const XML_Char *dflt,
int isrequired);
<p>Set a handler for attlist declarations in the DTD. This handler is
called for <em>each</em> attribute. So a single attlist declaration
with multiple attributes declared will generate multiple calls to this
handler. The <code>elname</code> parameter returns the name of the
element for which the attribute is being declared. The attribute name
is in the <code>attname</code> parameter. The attribute type is in the
<code>att_type</code> parameter. It is the string representing the
type in the declaration with whitespace removed.</p>
<p>The <code>dflt</code> parameter holds the default value. It will be
NULL in the case of "#IMPLIED" or "#REQUIRED" attributes. You can
distinguish these two cases by checking the <code>isrequired</code>
parameter, which will be true in the case of "#REQUIRED" attributes.
Attributes which are "#FIXED" will have also have a true
<code>isrequired</code>, but they will have the non-NULL fixed value
in the <code>dflt</code> parameter.</p>
<div class="handler">
<pre class="setter" id="XML_SetEntityDeclHandler">
XML_SetEntityDeclHandler(XML_Parser p,
XML_EntityDeclHandler handler);
<pre class="signature">
typedef void
(XMLCALL *XML_EntityDeclHandler)(void *userData,
const XML_Char *entityName,
int is_parameter_entity,
const XML_Char *value,
int value_length,
const XML_Char *base,
const XML_Char *systemId,
const XML_Char *publicId,
const XML_Char *notationName);
<p>Sets a handler that will be called for all entity declarations.
The <code>is_parameter_entity</code> argument will be non-zero in the
case of parameter entities and zero otherwise.</p>
<p>For internal entities (<code>&lt;!ENTITY foo "bar"&gt;</code>),
<code>value</code> will be non-NULL and <code>systemId</code>,
<code>publicId</code>, and <code>notationName</code> will all be NULL.
The value string is <em>not</em> NULL terminated; the length is
provided in the <code>value_length</code> parameter. Do not use
<code>value_length</code> to test for internal entities, since it is
legal to have zero-length values. Instead check for whether or not
<code>value</code> is NULL.</p> <p>The <code>notationName</code>
argument will have a non-NULL value only for unparsed entity
<div class="handler">
<pre class="setter" id="XML_SetUnparsedEntityDeclHandler">
XML_SetUnparsedEntityDeclHandler(XML_Parser p,
XML_UnparsedEntityDeclHandler h)
<pre class="signature">
typedef void
(XMLCALL *XML_UnparsedEntityDeclHandler)(void *userData,
const XML_Char *entityName,
const XML_Char *base,
const XML_Char *systemId,
const XML_Char *publicId,
const XML_Char *notationName);
<p>Set a handler that receives declarations of unparsed entities. These
are entity declarations that have a notation (NDATA) field:</p>
<div id="eg"><pre>
&lt;!ENTITY logo SYSTEM "images/logo.gif" NDATA gif&gt;
<p>This handler is obsolete and is provided for backwards
compatibility. Use instead <a href= "#XML_SetEntityDeclHandler"
<div class="handler">
<pre class="setter" id="XML_SetNotationDeclHandler">
XML_SetNotationDeclHandler(XML_Parser p,
XML_NotationDeclHandler h)
<pre class="signature">
typedef void
(XMLCALL *XML_NotationDeclHandler)(void *userData,
const XML_Char *notationName,
const XML_Char *base,
const XML_Char *systemId,
const XML_Char *publicId);
<p>Set a handler that receives notation declarations.</p>
<div class="handler">
<pre class="setter" id="XML_SetNotStandaloneHandler">
XML_SetNotStandaloneHandler(XML_Parser p,
XML_NotStandaloneHandler h)
<pre class="signature">
typedef int
(XMLCALL *XML_NotStandaloneHandler)(void *userData);
<p>Set a handler that is called if the document is not "standalone".
This happens when there is an external subset or a reference to a
parameter entity, but does not have standalone set to "yes" in an XML
declaration. If this handler returns <code>XML_STATUS_ERROR</code>,
then the parser will throw an <code>XML_ERROR_NOT_STANDALONE</code>
<h3><a name="position">Parse position and error reporting functions</a></h3>
<p>These are the functions you'll want to call when the parse
functions return <code>XML_STATUS_ERROR</code> (a parse error has
occurred), although the position reporting functions are useful outside
of errors. The position reported is the byte position (in the original
document or entity encoding) of the first of the sequence of
characters that generated the current event (or the error that caused
the parse functions to return <code>XML_STATUS_ERROR</code>.) The
exceptions are callbacks trigged by declarations in the document
prologue, in which case they exact position reported is somewhere in the
relevant markup, but not necessarily as meaningful as for other
<p>The position reporting functions are accurate only outside of the
DTD. In other words, they usually return bogus information when
called from within a DTD declaration handler.</p>
<pre class="fcndec" id="XML_GetErrorCode">
enum XML_Error XMLCALL
XML_GetErrorCode(XML_Parser p);
<div class="fcndef">
Return what type of error has occurred.
<pre class="fcndec" id="XML_ErrorString">
const XML_LChar * XMLCALL
XML_ErrorString(enum XML_Error code);
<div class="fcndef">
Return a string describing the error corresponding to code.
The code should be one of the enums that can be returned from
<code><a href= "#XML_GetErrorCode" >XML_GetErrorCode</a></code>.
<pre class="fcndec" id="XML_GetCurrentByteIndex">
XML_GetCurrentByteIndex(XML_Parser p);
<div class="fcndef">
Return the byte offset of the position. This always corresponds to
the values returned by <code><a href= "#XML_GetCurrentLineNumber"
>XML_GetCurrentLineNumber</a></code> and <code><a href=
"#XML_GetCurrentColumnNumber" >XML_GetCurrentColumnNumber</a></code>.
<pre class="fcndec" id="XML_GetCurrentLineNumber">
XML_GetCurrentLineNumber(XML_Parser p);
<div class="fcndef">
Return the line number of the position. The first line is reported as
<pre class="fcndec" id="XML_GetCurrentColumnNumber">
XML_GetCurrentColumnNumber(XML_Parser p);
<div class="fcndef">
Return the offset, from the beginning of the current line, of
the position.
<pre class="fcndec" id="XML_GetCurrentByteCount">
XML_GetCurrentByteCount(XML_Parser p);
<div class="fcndef">
Return the number of bytes in the current event. Returns
<code>0</code> if the event is inside a reference to an internal
entity and for the end-tag event for empty element tags (the later can
be used to distinguish empty-element tags from empty elements using
separate start and end tags).
<pre class="fcndec" id="XML_GetInputContext">
const char * XMLCALL
XML_GetInputContext(XML_Parser p,
int *offset,
int *size);
<div class="fcndef">
<p>Returns the parser's input buffer, sets the integer pointed at by
<code>offset</code> to the offset within this buffer of the current
parse position, and set the integer pointed at by <code>size</code> to
the size of the returned buffer.</p>
<p>This should only be called from within a handler during an active
parse and the returned buffer should only be referred to from within
the handler that made the call. This input buffer contains the
untranslated bytes of the input.</p>
<p>Only a limited amount of context is kept, so if the event
triggering a call spans over a very large amount of input, the actual
parse position may be before the beginning of the buffer.</p>
<p>If <code>XML_CONTEXT_BYTES</code> is not defined, this will always
return NULL.</p>
<h3><a name="miscellaneous">Miscellaneous functions</a></h3>
<p>The functions in this section either obtain state information from
the parser or can be used to dynamicly set parser options.</p>
<pre class="fcndec" id="XML_SetUserData">
XML_SetUserData(XML_Parser p,
void *userData);
<div class="fcndef">
This sets the user data pointer that gets passed to handlers. It
overwrites any previous value for this pointer. Note that the
application is responsible for freeing the memory associated with
<code>userData</code> when it is finished with the parser. So if you
call this when there's already a pointer there, and you haven't freed
the memory associated with it, then you've probably just leaked
<pre class="fcndec" id="XML_GetUserData">
void * XMLCALL
XML_GetUserData(XML_Parser p);
<div class="fcndef">
This returns the user data pointer that gets passed to handlers.
It is actually implemented as a macro.
<pre class="fcndec" id="XML_UseParserAsHandlerArg">
XML_UseParserAsHandlerArg(XML_Parser p);
<div class="fcndef">
After this is called, handlers receive the parser in their
<code>userData</code> arguments. The user data can still be obtained
using the <code><a href= "#XML_GetUserData"
>XML_GetUserData</a></code> function.
<pre class="fcndec" id="XML_SetBase">
enum XML_Status XMLCALL
XML_SetBase(XML_Parser p,
const XML_Char *base);
<div class="fcndef">
Set the base to be used for resolving relative URIs in system
identifiers. The return value is <code>XML_STATUS_ERROR</code> if
there's no memory to store base, otherwise it's
<pre class="fcndec" id="XML_GetBase">
const XML_Char * XMLCALL
XML_GetBase(XML_Parser p);
<div class="fcndef">
Return the base for resolving relative URIs.
<pre class="fcndec" id="XML_GetSpecifiedAttributeCount">
XML_GetSpecifiedAttributeCount(XML_Parser p);
<div class="fcndef">
When attributes are reported to the start handler in the atts vector,
attributes that were explicitly set in the element occur before any
attributes that receive their value from default information in an
ATTLIST declaration. This function returns the number of attributes
that were explicitly set times two, thus giving the offset in the
<code>atts</code> array passed to the start tag handler of the first
attribute set due to defaults. It supplies information for the last
call to a start handler. If called inside a start handler, then that
means the current call.
<pre class="fcndec" id="XML_GetIdAttributeIndex">
XML_GetIdAttributeIndex(XML_Parser p);
<div class="fcndef">
Returns the index of the ID attribute passed in the atts array in the
last call to <code><a href= "#XML_StartElementHandler"
>XML_StartElementHandler</a></code>, or -1 if there is no ID
attribute. If called inside a start handler, then that means the
current call.
<pre class="fcndec" id="XML_SetEncoding">
enum XML_Status XMLCALL
XML_SetEncoding(XML_Parser p,
const XML_Char *encoding);
<div class="fcndef">
Set the encoding to be used by the parser. It is equivalent to
passing a non-null encoding argument to the parser creation functions.
It must not be called after <code><a href= "#XML_Parse"
>XML_Parse</a></code> or <code><a href= "#XML_ParseBuffer"
>XML_ParseBuffer</a></code> have been called on the given parser.
Returns <code>XML_STATUS_OK</code> on success or
<code>XML_STATUS_ERROR</code> on error.
<pre class="fcndec" id="XML_SetParamEntityParsing">
XML_SetParamEntityParsing(XML_Parser p,
enum XML_ParamEntityParsing code);
<div class="fcndef">
This enables parsing of parameter entities, including the external
parameter entity that is the external DTD subset, according to
The choices for <code>code</code> are:
<pre class="fcndec" id="XML_UseForeignDTD">
enum XML_Error XMLCALL
XML_UseForeignDTD(XML_Parser parser, XML_Bool useDTD);
<div class="fcndef">
<p>This function allows an application to provide an external subset
for the document type declaration for documents which do not specify
an external subset of their own. For documents which specify an
external subset in their DOCTYPE declaration, the application-provided
subset will be ignored. If the document does not contain a DOCTYPE
declaration at all and <code>useDTD</code> is true, the
application-provided subset will be parsed, but the
<code>startDoctypeDeclHandler</code> and
<code>endDoctypeDeclHandler</code> functions, if set, will not be
called. The setting of parameter entity parsing, controlled using
<code><a href= "#XML_SetParamEntityParsing"
>XML_SetParamEntityParsing</a></code>, will be honored.</p>
<p>The application-provided external subset is read by calling the
external entity reference handler set via <code><a href=
>XML_SetExternalEntityRefHandler</a></code> with both
<code>publicId</code> and <code>systemId</code> set to NULL.</p>
<p>If this function is called after parsing has begun, it returns
<code>useDTD</code>. If called when Expat has been compiled without
DTD support, it returns
<code>XML_ERROR_FEATURE_REQUIRES_XML_DTD</code>. Otherwise, it
returns <code>XML_ERROR_NONE</code>.</p>
<p><b>Note:</b> For the purpose of checking WFC: Entity Declared, passing
<code>useDTD == XML_TRUE</code> will make the parser behave as if
the document had a DTD with an external subset. This holds true even if
the external entity reference handler returns without action.</p>
<pre class="fcndec" id="XML_SetReturnNSTriplet">
XML_SetReturnNSTriplet(XML_Parser parser,
int do_nst);
<div class="fcndef">
This function only has an effect when using a parser created with
<code><a href= "#XML_ParserCreateNS" >XML_ParserCreateNS</a></code>,
i.e. when namespace processing is in effect. The <code>do_nst</code>
sets whether or not prefixes are returned with names qualified with a
namespace prefix. If this function is called with <code>do_nst</code>
non-zero, then afterwards namespace qualified names (that is qualified
with a prefix as opposed to belonging to a default namespace) are
returned as a triplet with the three parts separated by the namespace
separator specified when the parser was created. The order of
returned parts is URI, local name, and prefix.</p> <p>If
<code>do_nst</code> is zero, then namespaces are reported in the
default manner, URI then local_name separated by the namespace
<pre class="fcndec" id="XML_DefaultCurrent">
XML_DefaultCurrent(XML_Parser parser);
<div class="fcndef">
This can be called within a handler for a start element, end element,
processing instruction or character data. It causes the corresponding
markup to be passed to the default handler set by <code><a
href="#XML_SetDefaultHandler" >XML_SetDefaultHandler</a></code> or
<code><a href="#XML_SetDefaultHandlerExpand"
>XML_SetDefaultHandlerExpand</a></code>. It does nothing if there is
not a default handler.
<pre class="fcndec" id="XML_ExpatVersion">
<div class="fcndef">
Return the library version as a string (e.g. <code>"expat_1.95.1"</code>).
<pre class="fcndec" id="XML_ExpatVersionInfo">
struct XML_Expat_Version XMLCALL
<pre class="signature">
typedef struct {
int major;
int minor;
int micro;
} XML_Expat_Version;
<div class="fcndef">
Return the library version information as a structure.
Some macros are also defined that support compile-time tests of the
library version:
Testing these constants is currently the best way to determine if
particular parts of the Expat API are available.
<pre class="fcndec" id="XML_GetFeatureList">
const XML_Feature * XMLCALL
<pre class="signature">
enum XML_FeatureEnum {
typedef struct {
enum XML_FeatureEnum feature;
XML_LChar *name;
long int value;
} XML_Feature;
<div class="fcndef">
<p>Returns a list of "feature" records, providing details on how
Expat was configured at compile time. Most applications should not
need to worry about this, but this information is otherwise not
available from Expat. This function allows code that does need to
check these features to do so at runtime.</p>
<p>The return value is an array of <code>XML_Feature</code>,
terminated by a record with a <code>feature</code> of
<code>XML_FEATURE_END</code> and <code>name</code> of NULL,
identifying the feature-test macros Expat was compiled with. Since an
application that requires this kind of information needs to determine
the type of character the <code>name</code> points to, records for the
<code>XML_FEATURE_SIZEOF_XML_LCHAR</code> will be located at the
beginning of the list, followed by <code>XML_FEATURE_UNICODE</code>
and <code>XML_FEATURE_UNICODE_WCHAR_T</code>, if they are present at
<p>Some features have an associated value. If there isn't an
associated value, the <code>value</code> field is set to 0. At this
time, the following features have been defined to have values:</p>
<dd>The number of bytes occupied by one <code>XML_Char</code>
<dd>The number of bytes occupied by one <code>XML_LChar</code>
<dd>The maximum number of characters of context which can be
reported by <code><a href= "#XML_GetInputContext"
<pre class="fcndec" id="XML_FreeContentModel">
XML_FreeContentModel(XML_Parser parser, XML_Content *model);
<div class="fcndef">
Function to deallocate the <code>model</code> argument passed to the
<code>XML_ElementDeclHandler</code> callback set using <code><a
href="#XML_SetElementDeclHandler" >XML_ElementDeclHandler</a></code>.
This function should not be used for any other purpose.
<p>The following functions allow external code to share the memory
allocator an <code>XML_Parser</code> has been configured to use. This
is especially useful for third-party libraries that interact with a
parser object created by application code, or heavily layered
applications. This can be essential when using dynamically loaded
libraries which use different C standard libraries (this can happen on
Windows, at least).</p>
<pre class="fcndec" id="XML_MemMalloc">
void * XMLCALL
XML_MemMalloc(XML_Parser parser, size_t size);
<div class="fcndef">
Allocate <code>size</code> bytes of memory using the allocator the
<code>parser</code> object has been configured to use. Returns a
pointer to the memory or NULL on failure. Memory allocated in this
way must be freed using <code><a href="#XML_MemFree"
<pre class="fcndec" id="XML_MemRealloc">
void * XMLCALL
XML_MemRealloc(XML_Parser parser, void *ptr, size_t size);
<div class="fcndef">
Allocate <code>size</code> bytes of memory using the allocator the
<code>parser</code> object has been configured to use.
<code>ptr</code> must point to a block of memory allocated by <code><a
href="#XML_MemMalloc" >XML_MemMalloc</a></code> or
<code>XML_MemRealloc</code>, or be NULL. This function tries to
expand the block pointed to by <code>ptr</code> if possible. Returns
a pointer to the memory or NULL on failure. On success, the original
block has either been expanded or freed. On failure, the original
block has not been freed; the caller is responsible for freeing the
original block. Memory allocated in this way must be freed using
<code><a href="#XML_MemFree"
<pre class="fcndec" id="XML_MemFree">
XML_MemFree(XML_Parser parser, void *ptr);
<div class="fcndef">
Free a block of memory pointed to by <code>ptr</code>. The block must
have been allocated by <code><a href="#XML_MemMalloc"
>XML_MemMalloc</a></code> or <code>XML_MemRealloc</code>, or be NULL.
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