我想从 xml 输入的文本节点中提取值。我从网上获得了以下代码，因为 libxml 的官方文档有许多损坏的链接，其中 sax 解析器就是其中之一。请帮我获取文本节点的值。在 startElementNs 中，当我尝试查找我的文本节点时，我得到 NULL。感谢这里的任何帮助。
我的 xml 看起来像这样：
<a>
<b>
<c> text values </c>
</b>
</a>
我的代码如下所示：
#include <stdio.h>
#include <assert.h>
#include <memory.h>
#include <libxml/xmlmemory.h>
#include <libxml/parser.h>
#include <string>
class ParseFSM
{
public:
/** SAX2 callback when an element start has been detected by the parser. It provides the namespace informations for the element, as well as the new namespace declarations on the element.
ctx: the user data (XML parser context)
localname: the local name of the element
prefix: the element namespace prefix if available
URI: the element namespace name if available
nb_namespaces: number of namespace definitions on that node
namespaces: pointer to the array of prefix/URI pairs namespace definitions
nb_attributes: the number of attributes on that node
nb_defaulted: the number of defaulted attributes. The defaulted ones are at the end of the array
attributes: pointer to the array of (localname/prefix/URI/value/end) attribute values.
**/
static void startElementNs (void *ctx,
const xmlChar * localname,
const xmlChar * prefix,
const xmlChar * URI,
int nb_namespaces,
const xmlChar ** namespaces,
int nb_attributes,
int nb_defaulted, const xmlChar ** attributes)
{
ParseFSM & fsm = *(static_cast < ParseFSM * >(ctx));
printf ("startElementNs: name = '%s' prefix = '%s' uri = (%p)'%s'\n", localname, prefix, URI, URI);
for (int indexNamespace = 0; indexNamespace < nb_namespaces; ++indexNamespace)
{
const xmlChar *prefix = namespaces[indexNamespace * 2];
const xmlChar *nsURI = namespaces[indexNamespace * 2 + 1];
printf (" namespace: name='%s' uri=(%p)'%s'\n", prefix, nsURI, nsURI);
}
unsigned int index = 0;
for (int indexAttribute = 0; indexAttribute < nb_attributes; ++indexAttribute, index += 5)
{
const xmlChar *localname = attributes[index];
const xmlChar *prefix = attributes[index + 1];
const xmlChar *nsURI = attributes[index + 2];
const xmlChar *valueBegin = attributes[index + 3];
const xmlChar *valueEnd = attributes[index + 4];
std::string value ((const char *) valueBegin, (const char *) valueEnd);
printf (" %sattribute: localname='%s', prefix='%s', uri=(%p)'%s', value='%s'\n", indexAttribute >= (nb_attributes - nb_defaulted) ? "defaulted " : "", localname, prefix, nsURI, nsURI, value.c_str ());
}
}
/** SAX2 callback when an element end has been detected by the parser. It provides the namespace informations for the element.
ctx: the user data (XML parser context)
localname: the local name of the element
prefix: the element namespace prefix if available
URI: the element namespace name if available
**/
static void endElementNs (void *ctx,
const xmlChar * localname,
const xmlChar * prefix, const xmlChar * URI)
{
ParseFSM & fsm = *(static_cast < ParseFSM * >(ctx));
printf ("endElementNs: name = '%s' prefix = '%s' uri = '%s'\n", localname,
prefix, URI);
}
/** Display and format an error messages, callback.
ctx: an XML parser context
msg: the message to display/transmit
...: extra parameters for the message display
*/
static void error (void *ctx, const char *msg, ...)
{
ParseFSM & fsm = *(static_cast < ParseFSM * >(ctx));
va_list args;
va_start (args, msg);
vprintf (msg, args);
va_end (args);
}
/** Display and format a warning messages, callback.
ctx: an XML parser context
msg: the message to display/transmit
...: extra parameters for the message display
*/
static void warning (void *ctx, const char *msg, ...)
{
ParseFSM & fsm = *(static_cast < ParseFSM * >(ctx));
va_list args;
va_start (args, msg);
vprintf (msg, args);
va_end (args);
}
};
int
main (int argc, const char *argv[])
{
std::string xmlIn = "<a><b><c> text values </c> </b> </a>"
/*
* this initialize the library and check potential ABI mismatches
* between the version it was compiled for and the actual shared
* library used.
*/
LIBXML_TEST_VERSION xmlSAXHandler saxHandler; // See http://xmlsoft.org/html/libxml-tree.html#xmlSAXHandler
memset (&saxHandler, 0, sizeof (saxHandler));
// Using xmlSAXVersion( &saxHandler, 2 ) generate crash as it sets plenty of other pointers...
saxHandler.initialized = XML_SAX2_MAGIC; // so we do this to force parsing as SAX2.
saxHandler.startElementNs = &ParseFSM::startElementNs;
saxHandler.endElementNs = &ParseFSM::endElementNs;
saxHandler.warning = &ParseFSM::warning;
saxHandler.error = &ParseFSM::error;
ParseFSM fsm;
int result =
xmlSAXUserParseMemory (&saxHandler, &fsm, xmlIn.c_str (),
int (xmlIn.length ()));
if (result != 0)
{
printf ("Failed to parse document.\n");
return 1;
}
/*
* Cleanup function for the XML library.
*/
xmlCleanupParser ();
/*
* this is to debug memory for regression tests
*/
xmlMemoryDump ();
return 0;
}