How can libxml2 be used to parse data from XML?

问题:

I have looked around at the libxml2 code samples and I am confused on how to piece them all together.

What are the steps needed when using libxml2 to just parse or extract data from an XML file?

I would like to get hold of, and possibly store information for, certain attributes. How is this done?

回答1:

I believe you first need to create a Parse tree. Maybe this article can help, look through the section which says How to Parse a Tree with Libxml2.

回答2:

I found these two resources helpful when I was learning to use libxml2 to build a rss feed parser.

Tutorial with SAX interface

Tutorial using the DOM Tree (code example for getting an attribute value included)

回答3:

libxml2 provides various examples showing basic usage.

http://xmlsoft.org/examples/index.html

For your stated goals, tree1.c would probably be most relevant.

tree1.c: Navigates a tree to print element names

Parse a file to a tree, use xmlDocGetRootElement() to get the root element, then walk the document and print all the element name in document order.

http://xmlsoft.org/examples/tree1.c

Once you have an xmlNode struct for an element, the "properties" member is a linked list of attributes. Each xmlAttr object has a "name" and "children" object (which are the name/value for that attribute, respectively), and a "next" member which points to the next attribute (or null for the last one).

http://xmlsoft.org/html/libxml-tree.html#xmlNode

http://xmlsoft.org/html/libxml-tree.html#xmlAttr

回答4:

Here, I mentioned complete process to extract XML/HTML data from file on windows platform.

1. First download pre-compiled .dll form http://xmlsoft.org/sources/win32/

2. Also download its dependency iconv.dll and zlib1.dll from the same page

3. Extract all .zip files into the same directory. For Ex: D:\demo\

4. Copy iconv.dll, zlib1.dll and libxml2.dll into c:\windows\system32 deirectory

5. Make libxml_test.cpp file and copy following code into that file.

   #include <stdio.h>
   #include <string.h>
   #include <stdlib.h>
   #include <libxml/HTMLparser.h>
   
   void traverse_dom_trees(xmlNode * a_node)
   {
       xmlNode *cur_node = NULL;
   
       if(NULL == a_node)
       {
           //printf("Invalid argument a_node %p\n", a_node);
           return;
       }
   
       for (cur_node = a_node; cur_node; cur_node = cur_node->next) 
       {
           if (cur_node->type == XML_ELEMENT_NODE) 
           {
               /* Check for if current node should be exclude or not */
               printf("Node type: Text, name: %s\n", cur_node->name);
           }
           else if(cur_node->type == XML_TEXT_NODE)
           {
               /* Process here text node, It is available in cpStr :TODO: */
               printf("node type: Text, node content: %s,  content length %d\n", (char *)cur_node->content, strlen((char *)cur_node->content));
           }
           traverse_dom_trees(cur_node->children);
       }
   }
   
   int main(int argc, char **argv) 
   {
       htmlDocPtr doc;
       xmlNode *roo_element = NULL;
   
       if (argc != 2)  
       {
           printf("\nInvalid argument\n");
           return(1);
       }
   
       /* Macro to check API for match with the DLL we are using */
       LIBXML_TEST_VERSION    
   
       doc = htmlReadFile(argv[1], NULL, HTML_PARSE_NOBLANKS | HTML_PARSE_NOERROR | HTML_PARSE_NOWARNING | HTML_PARSE_NONET);
       if (doc == NULL) 
       {
           fprintf(stderr, "Document not parsed successfully.\n");
           return 0;
       }
   
       roo_element = xmlDocGetRootElement(doc);
   
       if (roo_element == NULL) 
       {
           fprintf(stderr, "empty document\n");
           xmlFreeDoc(doc);
           return 0;
       }
   
       printf("Root Node is %s\n", roo_element->name);
       traverse_dom_trees(roo_element);
   
       xmlFreeDoc(doc);       // free document
       xmlCleanupParser();    // Free globals
       return 0;
   }
   

6. Open Visual Studio Command Promt

7. Go To D:\demo directory

8. execute cl libxml_test.cpp /I".\libxml2-2.7.8.win32\include" /I".\iconv-1.9.2.win32\include" /link libxml2-2.7.8.win32\lib\libxml2.lib command

9. Run binary using libxml_test.exe test.html command(Here test.html may be any valid HTML file)