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ÇëÎÊ£ºÔõôÐÞ¸ÄxmlÎļþÀïÃ棬nodeµÄelementµÄÄÚÈÝ ÏëÓÃCдһ¸öС³ÌÐò£¬À´ÐÞ¸ÄÖ¸¶¨½ÚµãµÄÔªËصÄÄÚÈÝ£¬ÔÚÍøÉϲ鵽ÈçÏ´úÂ룺 £½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½ /** * section:  XPath * synopsis:  Load a document, locate subelements with XPath, modify *              said elements and save the resulting document. * purpose:  Shows how to make a full round-trip from a load/edit/save * usage: xpath2 <xml-file> <xpath-expr> <new-value> * test: xpath2 test3.xml '//discarded' discarded > xpath2.tmp ; diff xpath2.tmp xpath2.res ; rm xpath2.tmp * author:  Aleksey Sanin and Daniel Veillard * copy:  see Copyright for the status of this software. */ #include <stdlib.h> #include <stdio.h> #include <string.h> #include <assert.h> #include <libxml/tree.h> #include <libxml/parser.h> #include <libxml/xpath.h> #include <libxml/xpathInternals.h> static void usage(const char *name); static int example4(const char *filename, const xmlChar * xpathExpr,                     const xmlChar * value); static void update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar * value); int main(int argc, char **argv) {     /* Parse command line and process file */     if (argc != 4) {  fprintf(stderr, "Error: wrong number of arguments.\n");  usage(argv[0]);  return(-1);     }          /* Init libxml */          xmlInitParser();     LIBXML_TEST_VERSION     /* Do the main job */     if (example4(argv[1], BAD_CAST argv[2], BAD_CAST argv[3])) {  usage(argv[0]);  return(-1);     }     /* Shutdown libxml */     xmlCleanupParser();          /*      * this is to debug memory for regression tests      */     xmlMemoryDump();     return 0; } /** * usage: * @name:  the program name. * * Prints usage information. */ static void usage(const char *name) {     assert(name);          fprintf(stderr, "Usage: %s <xml-file> <xpath-expr> <value>\n", name); } /** * example4: * @filename:  the input XML filename. * @xpathExpr:  the xpath expression for evaluation. * @value:  the new node content. * * Parses input XML file, evaluates XPath expression and update the nodes * then print the result. * * Returns 0 on success and a negative value otherwise. */ static int example4(const char* filename, const xmlChar* xpathExpr, const xmlChar* value) {     xmlDocPtr doc;     xmlXPathContextPtr xpathCtx;     xmlXPathObjectPtr xpathObj;          assert(filename);     assert(xpathExpr);     assert(value);     /* Load XML document */     doc = xmlParseFile(filename);     if (doc == NULL) {  fprintf(stderr, "Error: unable to parse file \"%s\"\n", filename);  return(-1);     }     /* Create xpath evaluation context */     xpathCtx = xmlXPathNewContext(doc);     if(xpathCtx == NULL) {         fprintf(stderr,"Error: unable to create new XPath context\n");         xmlFreeDoc(doc);         return(-1);     }          /* Evaluate xpath expression */     xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);     if(xpathObj == NULL) {         fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", xpathExpr);         xmlXPathFreeContext(xpathCtx);         xmlFreeDoc(doc);         return(-1);     }     /* update selected nodes */     update_xpath_nodes(xpathObj->nodesetval, value);          /* Cleanup of XPath data */     xmlXPathFreeObject(xpathObj);     xmlXPathFreeContext(xpathCtx);     /* dump the resulting document */     xmlDocDump(stdout, doc);     /* free the document */     xmlFreeDoc(doc);          return(0); } /** * update_xpath_nodes: * @nodes:  the nodes set. * @value:  the new value for the node(s) * * Prints the @nodes content to @output. */ static void update_xpath_nodes(xmlNodeSetPtr nodes, const xmlChar* value) {     int size;     int i;          assert(value);     size = (nodes) ? nodes->nodeNr : 0;          /*      * NOTE: the nodes are processed in reverse order, i.e. reverse document      *       order because xmlNodeSetContent can actually free up descendant      *       of the node and such nodes may have been selected too ! Handling      *       in reverse order ensure that descendant are accessed first, before      *       they get removed. Mixing XPath and modifications on a tree must be      *       done carefully !      */     for(i = size - 1; i >= 0; i--) {  assert(nodes->nodeTab[i]);    xmlNodeSetContent(nodes->nodeTab[i], value);  /*   * All the elements returned by an XPath query are pointers to   * elements from the tree *except* namespace nodes where the XPath   * semantic is different from the implementation in libxml2 tree.   * As a result when a returned node set is freed when   * xmlXPathFreeObject() is called, that routine must check the   * element type. But node from the returned set may have been removed   * by xmlNodeSetContent() resulting in access to freed data.   * This can be exercised by running   *       valgrind xpath2 test3.xml '//discarded' discarded   * There is 2 ways around it:   *   - make a copy of the pointers to the nodes from the result set   *     then call xmlXPathFreeObject() and then modify the nodes   * or   *   - remove the reference to the modified nodes from the node set   *     as they are processed, if they are not namespace nodes.   */  if (nodes->nodeTab[i]->type != XML_NAMESPACE_DECL)      nodes->nodeTab[i] = NULL;     } } £½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½£½ µ«ÊÇÀïÃæµÄexample4µÄupdate ºÃÏñûÓй¤×÷£¬ÓÐÅóÓÑÄÜ°ï°ïÎÒÂ𣿠   Êղؠ  ·ÖÏí   ¶¥(0)

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