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* synopsis: Evaluate XPath expression and prints result node set.
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* purpose: Shows how to evaluate XPath expression and register
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* known namespaces in XPath context.
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* usage: xpath1 <xml-file> <xpath-expr> [<known-ns-list>]
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* test: ./xpath1 test3.xml '//child2' > xpath1.tmp ; diff xpath1.tmp xpath1.res ; rm xpath1.tmp
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* author: Aleksey Sanin
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* copy: see Copyright for the status of this software.
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#include <libxml/tree.h>
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#include <libxml/parser.h>
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#include <libxml/xpath.h>
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#include <libxml/xpathInternals.h>
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#if defined(LIBXML_XPATH_ENABLED) && defined(LIBXML_SAX1_ENABLED)
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static void usage(const char *name);
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int execute_xpath_expression(const char* filename, const xmlChar* xpathExpr, const xmlChar* nsList);
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int register_namespaces(xmlXPathContextPtr xpathCtx, const xmlChar* nsList);
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void print_xpath_nodes(xmlNodeSetPtr nodes, FILE* output);
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main(int argc, char **argv) {
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/* Parse command line and process file */
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if((argc < 3) || (argc > 4)) {
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fprintf(stderr, "Error: wrong number of arguments.\n");
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if(execute_xpath_expression(argv[1], BAD_CAST argv[2], (argc > 3) ? BAD_CAST argv[3] : NULL) < 0) {
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* this is to debug memory for regression tests
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* @name: the program name.
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* Prints usage information.
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usage(const char *name) {
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fprintf(stderr, "Usage: %s <xml-file> <xpath-expr> [<known-ns-list>]\n", name);
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fprintf(stderr, "where <known-ns-list> is a list of known namespaces\n");
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fprintf(stderr, "in \"<prefix1>=<href1> <prefix2>=href2> ...\" format\n");
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* execute_xpath_expression:
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* @filename: the input XML filename.
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* @xpathExpr: the xpath expression for evaluation.
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* @nsList: the optional list of known namespaces in
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* "<prefix1>=<href1> <prefix2>=href2> ..." format.
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* Parses input XML file, evaluates XPath expression and prints results.
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* Returns 0 on success and a negative value otherwise.
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execute_xpath_expression(const char* filename, const xmlChar* xpathExpr, const xmlChar* nsList) {
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xmlXPathContextPtr xpathCtx;
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xmlXPathObjectPtr xpathObj;
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/* Load XML document */
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doc = xmlParseFile(filename);
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fprintf(stderr, "Error: unable to parse file \"%s\"\n", filename);
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/* Create xpath evaluation context */
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xpathCtx = xmlXPathNewContext(doc);
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if(xpathCtx == NULL) {
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fprintf(stderr,"Error: unable to create new XPath context\n");
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/* Register namespaces from list (if any) */
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if((nsList != NULL) && (register_namespaces(xpathCtx, nsList) < 0)) {
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fprintf(stderr,"Error: failed to register namespaces list \"%s\"\n", nsList);
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xmlXPathFreeContext(xpathCtx);
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/* Evaluate xpath expression */
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xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
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if(xpathObj == NULL) {
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fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", xpathExpr);
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xmlXPathFreeContext(xpathCtx);
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print_xpath_nodes(xpathObj->nodesetval, stdout);
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xmlXPathFreeObject(xpathObj);
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xmlXPathFreeContext(xpathCtx);
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* register_namespaces:
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* @xpathCtx: the pointer to an XPath context.
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* @nsList: the list of known namespaces in
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* "<prefix1>=<href1> <prefix2>=href2> ..." format.
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* Registers namespaces from @nsList in @xpathCtx.
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* Returns 0 on success and a negative value otherwise.
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register_namespaces(xmlXPathContextPtr xpathCtx, const xmlChar* nsList) {
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nsListDup = xmlStrdup(nsList);
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if(nsListDup == NULL) {
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fprintf(stderr, "Error: unable to strdup namespaces list\n");
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while(next != NULL) {
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while((*next) == ' ') next++;
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if((*next) == '\0') break;
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next = (xmlChar*)xmlStrchr(next, '=');
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fprintf(stderr,"Error: invalid namespaces list format\n");
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next = (xmlChar*)xmlStrchr(next, ' ');
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/* do register namespace */
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if(xmlXPathRegisterNs(xpathCtx, prefix, href) != 0) {
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fprintf(stderr,"Error: unable to register NS with prefix=\"%s\" and href=\"%s\"\n", prefix, href);
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* @nodes: the nodes set.
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* @output: the output file handle.
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* Prints the @nodes content to @output.
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print_xpath_nodes(xmlNodeSetPtr nodes, FILE* output) {
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size = (nodes) ? nodes->nodeNr : 0;
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fprintf(output, "Result (%d nodes):\n", size);
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for(i = 0; i < size; ++i) {
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assert(nodes->nodeTab[i]);
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if(nodes->nodeTab[i]->type == XML_NAMESPACE_DECL) {
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ns = (xmlNsPtr)nodes->nodeTab[i];
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cur = (xmlNodePtr)ns->next;
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fprintf(output, "= namespace \"%s\"=\"%s\" for node %s:%s\n",
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ns->prefix, ns->href, cur->ns->href, cur->name);
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fprintf(output, "= namespace \"%s\"=\"%s\" for node %s\n",
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ns->prefix, ns->href, cur->name);
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} else if(nodes->nodeTab[i]->type == XML_ELEMENT_NODE) {
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cur = nodes->nodeTab[i];
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fprintf(output, "= element node \"%s:%s\"\n",
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cur->ns->href, cur->name);
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fprintf(output, "= element node \"%s\"\n",
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cur = nodes->nodeTab[i];
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fprintf(output, "= node \"%s\": type %d\n", cur->name, cur->type);
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fprintf(stderr, "XPath support not compiled in\n");