static void
handle_error(void *arg,
        const char *msg,
        int severity,
        xmlTextReaderLocatorPtr locator)
{
    printf("%s\n", __FUNCTION__);
}

...

    xmlTextReaderPtr reader;
    int ret;

    reader = xmlReaderForFile(filename, NULL, 0);
    if (reader != NULL) {
        if (0 < xmlTextReaderSchemaValidate(reader, xsd)) {
            fprintf(stderr, "%s : failed to validate.", filename);
        }

        xmlTextReaderSetErrorHandler(reader, (xmlTextReaderErrorFunc) handle_error, NULL);


...