Get values from XML <tag> in C++ using libxml2 - c++

Question

I am having a hard time to get the values from a XML file. We are using libxml2 and python (output to *.txt) and then C++ to read the *.txt file.
I would like to use libxml2 in C++ without going through Python. My problem is the reader (see example below). BTW: I do not get much from this example code from http://xmlsoft.org/examples/index.html#reader1.c
Could someone tell me how i get the value = xmlTextReaderConstValue(reader);
into a string?
In summary: Loop through XMLdoc {if "XML-tag-" == 'tag' then store value/content of "XML-tag-" in mystring}
M
/**
* section: xmlReader
* synopsis: Parse an XML file with an xmlReader
* purpose: Demonstrate the use of xmlReaderForFile() to parse an XML file
* and dump the informations about the nodes found in the process.
* (Note that the XMLReader functions require libxml2 version later
* than 2.6.)
* usage: reader1 <filename>
* test: reader1 test2.xml > reader1.tmp && diff reader1.tmp $(srcdir)/reader1.res
* author: Daniel Veillard
* copy: see Copyright for the status of this software.
*/
#include <stdio.h>
#include <libxml/xmlreader.h>
#ifdef LIBXML_READER_ENABLED
/**
* processNode:
* #reader: the xmlReader
*
* Dump information about the current node
*/
static void
processNode(xmlTextReaderPtr reader) {
const xmlChar *name, *value;
name = xmlTextReaderConstName(reader);
if (name == NULL)
name = BAD_CAST "--";
value = xmlTextReaderConstValue(reader);
printf("%d %d %s %d %d",
xmlTextReaderDepth(reader),
xmlTextReaderNodeType(reader),
name,
xmlTextReaderIsEmptyElement(reader),
xmlTextReaderHasValue(reader));
if (value == NULL)
printf("\n");
else {
if (xmlStrlen(value) > 40)
printf(" %.40s...\n", value);
else
printf(" %s\n", value);
}
}
/**
* streamFile:
* #filename: the file name to parse
*
* Parse and print information about an XML file.
*/
static void
streamFile(const char *filename) {
xmlTextReaderPtr reader;
int ret;
reader = xmlReaderForFile(filename, NULL, 0);
if (reader != NULL) {
ret = xmlTextReaderRead(reader);
while (ret == 1) {
processNode(reader);
ret = xmlTextReaderRead(reader);
}
xmlFreeTextReader(reader);
if (ret != 0) {
fprintf(stderr, "%s : failed to parse\n", filename);
}
} else {
fprintf(stderr, "Unable to open %s\n", filename);
}
}
int main(int argc, char **argv) {
if (argc != 2)
return(1);
/*
* 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
streamFile(argv[1]);
/*
* Cleanup function for the XML library.
*/
xmlCleanupParser();
/*
* this is to debug memory for regression tests
*/
xmlMemoryDump();
return(0);
}
#else
int main(void) {
fprintf(stderr, "XInclude support not compiled in\n");
exit(1);
}
#endif

Answer 1

I've been using this cast to get the std::string out of the const xmlChar* :
my_std_string.assign(reinterpret_cast<const char*>(my_const_xmlchar_ptr));
Don't know if it's the best way but worked well.
I think that what you name the "XML-tag-" is actualy the return of xmlTextReaderConstName(reader), name, wich is a const xmlChar*. (See libxml2 xmlreader)
I suggest the use of string::compare to test the string equality with your "-tag-".
If strings match, you can then get the value, a const xmlChar* again, with the xmlTextReaderConstValue(reader); function, cast into a string with the same fashion way, then store it.

Answer 2

value is a C null-terminated (and statically allocated) string already.
If you want to get std::string, you can use something like:
std::string val = value;
If you want a C null-terminated string which will be owned by you:
xmlChar* val = xmlStrdup(value);