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Diffstat (limited to 'libxml2-2.9.10/doc/examples/xpath2.c')
| -rw-r--r-- | libxml2-2.9.10/doc/examples/xpath2.c | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/libxml2-2.9.10/doc/examples/xpath2.c b/libxml2-2.9.10/doc/examples/xpath2.c new file mode 100644 index 0000000..f604114 --- /dev/null +++ b/libxml2-2.9.10/doc/examples/xpath2.c @@ -0,0 +1,190 @@ +/** + * 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 $(srcdir)/xpath2.res + * 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> + +#if defined(LIBXML_XPATH_ENABLED) && defined(LIBXML_SAX1_ENABLED) && \ + defined(LIBXML_OUTPUT_ENABLED) + + +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; + } +} + +#else +int main(void) { + fprintf(stderr, "XPath support not compiled in\n"); + exit(1); +} +#endif |