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GNU libxml2 bcb开发包（343个子文件）

xmllint.1 11KB

xmlcatalog.1 6KB

Makefile.am 5KB

Makefile.am 2KB

testWriter.c 38KB

xpath1.c 6KB

xpath2.c 5KB

io1.c 4KB

parse4.c 3KB

tree2.c 3KB

reader2.c 3KB

reader4.c 3KB

reader3.c 3KB

reader1.c 2KB

tree1.c 2KB

parse2.c 2KB

includeconvert.c 2KB

parse3.c 1KB

includexpath.c 1KB

includekeyword.c 1KB

includeaddkeyword.c 1KB

parse1.c 1KB

io2.c 1KB

includegetattribute.c 1KB

includeaddattribute.c 1KB

style.css 820B

libxml2.devhelp 331KB

libxml2.dll 1.13MB

README.docs 679B

Libxml2-Logo-180x168.gif 8KB

libxml.gif 8KB

catalog.gif 6KB

structure.gif 5KB

DOM.gif 3KB

Libxml2-Logo-90x34.gif 3KB

smallfootonly.gif 3KB

redhat.gif 697B

parser.h 38KB

xmlerror.h 36KB

tree.h 36KB

schemasInternals.h 25KB

xmlwriter.h 21KB

xpathInternals.h 19KB

parserInternals.h 16KB

xpath.h 16KB

globals.h 14KB

valid.h 13KB

xmlreader.h 12KB

xmlIO.h 10KB

xmlunicode.h 10KB

HTMLparser.h 9KB

xmlversion.h 8KB

encoding.h 8KB

hash.h 6KB

xmlschemas.h 6KB

xmlmemory.h 6KB

relaxng.h 6KB

xmlstring.h 5KB

xmlregexp.h 5KB

debugXML.h 5KB

chvalid.h 5KB

xlink.h 5KB

catalog.h 5KB

SAX2.h 5KB

xmlschemastypes.h 5KB

entities.h 5KB

SAX.h 4KB

schematron.h 4KB

xmlautomata.h 4KB

xmlexports.h 4KB

HTMLtree.h 4KB

list.h 3KB

xpointer.h 3KB

nanoftp.h 3KB

DOCBparser.h 3KB

xinclude.h 3KB

c14n.h 3KB

uri.h 3KB

pattern.h 3KB

xmlsave.h 2KB

nanohttp.h 2KB

threads.h 2KB

dict.h 2KB

xmlmodule.h 1KB

APIfiles.html 316KB

APIsymbols.html 314KB

xml.html 236KB

libxml-tree.html 221KB

libxml2-tree.html 220KB

APIfunctions.html 209KB

libxml-parser.html 142KB

libxml2-xpathInternals.html 141KB

libxml-xpathInternals.html 139KB

libxml2-parser.html 134KB

libxml2-parserInternals.html 120KB

libxml-parserInternals.html 117KB

libxml-xmlwriter.html 114KB

libxml-xmlunicode.html 110KB

libxml-xmlreader.html 110KB

共 343 条

Libxml Tutorial

John Fleck <jfleck@inkstain.net>

Revision History

Revision 1 June 4, 2002

Initial draft

Revision 2 June 12, 2002

retrieving attribute value added

Revision 3 Aug. 31, 2002

freeing memory fix

Revision 4 Nov. 10, 2002

encoding discussion added

Revision 5 Dec. 15, 2002

more memory freeing changes

Revision 6 Jan. 26. 2003

add index

Revision 7 April 25, 2003

add compilation appendix

Revision 8 July 24, 2003

add XPath example

Revision 9 Feb. 14, 2004

Fix bug in XPath example

Revision 7 Aug. 24, 2004

Fix another bug in XPath example

Table of Contents

Introduction ...............................................................................2

Data Types ................................................................................2

Parsing the file ...........................................................................3

Retrieving Element Content .......................................................... 3

Using XPath to Retrieve Element Content ........................................ 4

Writing element content ............................................................... 6

Writing Attribute ........................................................................6

Retrieving Attributes ...................................................................7

Encoding Conversion ...................................................................8

A. Compilation ...........................................................................9

B. Sample Document ...................................................................9

C. Code for Keyword Example ......................................................9

D. Code for XPath Example ........................................................ 10

E. Code for Add Keyword Example .............................................. 12

F. Code for Add Attribute Example .............................................. 13

G. Code for Retrieving Attribute Value Example ............................. 14

H. Code for Encoding Conversion Example ................................... 15

I. Acknowledgements ................................................................ 16

Abstract

Libxml is a freely licensed C language library for handling XML, portable

across a large number of platforms. This tutorial provides examples of its basic

functions.

Introduction

Libxml is a C language library implementing functions for reading, creating and

manipulating XML data. This tutorial provides example code and explanations

of its basic functionality.

Libxml and more details about its use are available on the project home page.

Included there is complete API documentation. This tutorial is not meant to sub-

stitute for that complete documentation, but to illustrate the functions needed to

use the library to perform basic operations.

The tutorial is based on a simple XML application I use for articles I write. The

format includes metadata and the body of the article.

The example code in this tutorial demonstrates how to:

• Parse the document.

• Extract the text within a specified element.

• Add an element and its content.

• Add an attribute.

• Extract the value of an attribute.

Full code for the examples is included in the appendices.

Data Types

Libxml declares a number of data types we will encounter repeatedly, hiding the

messy stuff so you do not have to deal with it unless you have some specific

need.

xmlChar A basic replacement for char, a byte in a UTF-8

encoded string. If your data uses another encod-

ing, it must be converted to UTF-8 for use with

libxml's functions. More information on encoding

is available on the libxml encoding support web

page.

xmlDoc A structure containing the tree created by a parsed

doc. xmlDocPtr is a pointer to the structure.

xmlNodePtr and xml-

Node

A structure containing a single node. xmlNodePtr

is a pointer to the structure, and is used in travers-

ing the document tree.

Libxml Tutorial

Parsing the file

Parsing the file requires only the name of the file and a single function call, plus

error checking. Full code: Appendix C, Code for Keyword Example

❶ xmlDocPtr doc;

❷ xmlNodePtr cur;

❸ doc = xmlParseFile(docname);

❹ if (doc == NULL ) {

fprintf(stderr,"Document not parsed successfully. \n");

return;

}

❺ cur = xmlDocGetRootElement(doc);

❻ if (cur == NULL) {

fprintf(stderr,"empty document\n");

xmlFreeDoc(doc);

return;

}

❼ if (xmlStrcmp(cur->name, (const xmlChar *) "story")) {

fprintf(stderr,"document of the wrong type, root node != story");

xmlFreeDoc(doc);

return;

}

❶ Declare the pointer that will point to your parsed document.

❷ Declare a node pointer (you'll need this in order to interact with individual

nodes).

❹ Check to see that the document was successfully parsed. If it was not,

libxml will at this point register an error and stop.

Note

One common example of an error at this point is improper handling of

encoding. The XML standard requires documents stored with an encod-

ing other than UTF-8 or UTF-16 to contain an explicit declaration of

their encoding. If the declaration is there, libxml will automatically per-

form the necessary conversion to UTF-8 for you. More information on

XML's encoding requirements is contained in the standard.

❺ Retrieve the document's root element.

❻ Check to make sure the document actually contains something.

❼ In our case, we need to make sure the document is the right type. "story" is

the root type of the documents used in this tutorial.

Retrieving Element Content

Retrieving the content of an element involves traversing the document tree until

you find what you are looking for. In this case, we are looking for an element

called "keyword" contained within element called "story". The process to find

the node we are interested in involves tediously walking the tree. We assume

Libxml Tutorial

you already have an xmlDocPtr called doc and an xmlNodPtr called cur.

❶cur = cur->xmlChildrenNode;

❷while (cur != NULL) {

if ((!xmlStrcmp(cur->name, (const xmlChar *)"storyinfo"))){

parseStory (doc, cur);

}

cur = cur->next;

}

❶ Get the first child node of cur. At this point, cur points at the document

root, which is the element "story".

❷ This loop iterates through the elements that are children of "story", looking

for one called "storyinfo". That is the element that will contain the

"keywords" we are looking for. It uses the libxml string comparison func-

tion, xmlStrcmp. If there is a match, it calls the function parseStory.

void

parseStory (xmlDocPtr doc, xmlNodePtr cur) {

xmlChar *key;

❶ cur = cur->xmlChildrenNode;

❷ while (cur != NULL) {

if ((!xmlStrcmp(cur->name, (const xmlChar *)"keyword"))) {

❸ key = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1);

printf("keyword: %s\n", key);

xmlFree(key);

}

cur = cur->next;

}

return;

}

❶ Again we get the first child node.

❷ Like the loop above, we then iterate through the nodes, looking for one that

matches the element we're interested in, in this case "keyword".

❸ When we find the "keyword" element, we need to print its contents. Re-

member that in XML, the text contained within an element is a child node

of that element, so we turn to cur->xmlChildrenNode. To retrieve it,

we use the function xmlNodeListGetString, which also takes the

doc pointer as an argument. In this case, we just print it out.

Note

Because xmlNodeListGetString allocates memory for the string

it returns, you must use xmlFree to free it.

Using XPath to Retrieve Element

Content

In addition to walking the document tree to find an element, Libxml2 includes

Libxml Tutorial

support for use of XPath expressions to retrieve sets of nodes that match a spe-

cified criteria. Full documentation of the XPath API is here.

XPath allows searching through a document for nodes that match specified cri-

teria. In the example below we search through a document for the contents of all

keyword elements.

Note

A full discussion of XPath is beyond the scope of this document. For

details on its use, see the XPath specification.

Full code for this example is at Appendix D, Code for XPath Example.

Using XPath requires setting up an xmlXPathContext and then supplying the

XPath expression and the context to the xmlXPathEvalExpression func-

tion. The function returns an xmlXPathObjectPtr, which includes the set of

nodes satisfying the XPath expression.

xmlXPathObjectPtr

getnodeset (xmlDocPtr doc, xmlChar *xpath){

❶xmlXPathContextPtr context;

xmlXPathObjectPtr result;

❷context = xmlXPathNewContext(doc);

❸result = xmlXPathEvalExpression(xpath, context);

❹if(xmlXPathNodeSetIsEmpty(result->nodesetval)){

xmlXPathFreeObject(result);

printf("No result\n");

return NULL;

❶ First we declare our variables.

❷ Initialize the context variable.

❸ Apply the XPath expression.

❹ Check the result and free the memory allocated to result if no result is

found.

The xmlPathObjectPtr returned by the function contains a set of nodes and other

information needed to iterate through the set and act on the results. For this ex-

ample, our functions returns the xmlXPathObjectPtr. We use it to print the

contents of keyword nodes in our document. The node set object includes the

number of elements in the set (nodeNr) and an array of nodes (nodeTab):

❶for (i=0; i < nodeset->nodeNr; i++) {

❷keyword = xmlNodeListGetString(doc, nodeset->nodeTab[i]->xmlChildrenNode, 1);

printf("keyword: %s\n", keyword);

xmlFree(keyword);

}

❶ The value of nodeset->Nr holds the number of elements in the node

set. Here we use it to iterate through the array.

❷ Here we print the contents of each of the nodes returned.

Libxml Tutorial

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