Get values from XML in C++ using libxml2

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

I recommend pugixml (http://code.google.com/p/pugixml/). It's pretty easy and STL style. — Lucas Lima, Aug 27 '12 at 03:08
@LucasNunes: Thanks, but i cannot bring another xml lib into the project. — Michael, Aug 27 '12 at 03:24

Pascal Lécuyot · Answer 1 · 2012-08-28T12:07:52.230

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.

score 0 · Answer 2 · answered Aug 27 '12 at 07:12

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);

Get values from XML in C++ using libxml2

2 Answers2