XML数据提取可能是一项常见的任务，但是要直接使用此数据，您需要了解PHP如何解析XML。在PHP中解析XML涉及各种不同的功能，所有这些功能协同工作以从XML文档中提取数据。我将完成所有这些功能，并在最后将它们联系在一起。
xml_parser_create()
此函数用于创建解析器对象，该对象将在其余过程中使用。该对象用于存储数据和配置选项，并传递给所涉及的每个功能。
$xml_parser=xml_parser_create();
xml_set_element_handler()
接下来，我们需要设置将在脚本解析中使用的函数。该xml_set_handler()方法采用以下参数：
XML解析器参考：这是对使用xml_parser_create创建的解析器的参考function()。
起始元素：这是对函数的回调引用，当解析器运行时找到起始元素时将调用该函数。
Endelement：这是对函数的回调引用，当解析器运行时找到end元素时将调用该函数。
最后两个参数必须是具有特定占用空间的函数。这意味着它们需要具有正确的参数编号，但是您可以随心所欲地调用它。这是对该函数的调用示例xml_set_element_handler()。
xml_set_element_handler($xml_parser,"startElement","endElement");
的startElement()和endElement()功能将自动由XML解析器对象时，事情在运动设定被调用。
startElement()功能
在该函数的调用上方，xml_set_element_handler()您需要设置一个读取起始元素数据的方法。该方法必须具有以下参数：
解析器：这是在对xml_parser_create的调用中创建的xml解析器对象。
Name：开始元素的名称。
Attribs：这是属性的关联数组的开始元素包含。
因此，您的函数可能看起来像这样：
function startElement($xmlParser, $name, $attribs) {
echo "Start: " . $name ."
";
}所有这些操作将打印出元素的名称，但是您可以做更多的事情。例如，假设您的元素之一被称为
,youcanuseaniforswitchstatementtostorethisvalueinavariableforuselater.Likethis:<code><pre>functionstartElement($xmlParser,$name,$attribs){
global$variable;
switch($name){
case'title':
$variable=$name;
break;
}
}
</pre></code><p>RememberthatyouwillneedtoputthisfunctiondeclarationBEFOREthecallfor<code>xml_set_element_handler()</code>,PHPneedstoknowaboutthismethodsothatitcanpointtheparsertowardsit.</p><h4><code>endElement()</code>function</h4><p>Thisfunctioniscalledwhentheparserencountersaxmlclosingelement.Inanoppositeoperationasbeforeyoumightneedtoclearthevariableyoustoredduringthestartelementfunction.AgainthisdeclerationMUSTbebeforethecallforxml_set_element_handler.Notethatifthetagisselfclosingthentherewillbenoendelement.Thefunctionmusthavethefollowingparameters.</p><ul><li><strong>xml_parser</strong>:Theparsercreatedinthecalltoxml_parser_create.</li><li><strong>name</strong>:Thenameoftheelement.</li></ul><p>Thefollowingcodewilljustprintofthenameoftheendelement,youcanusethisfunctiontooverrightanythingthatmayhavehappenedinthestartElementfunction.Forexample,youmayhavesetavalueinthe<code>startElement()</code>tokeeptrackofthedepthoftheparserintotheXMLdocument,youcanusethismethodtoreduceit.Thismightbeimportantifthereismorethanoneelementwiththesamename,butinadifferentcontext.</p><code><pre>functionendElement($parser,$name)
{
echo"End:".$name."<br/>";
}
</pre></code><h3><code>xml_set_character_data_handler()</code></h3><p>Thenextfunctiontocallisxml_set_character_data_handler.Thistakestwoparameters:</p><ul><li><strong>xml_parser</strong>:Thisisacallbackreferencetothexmlparserthatwascreatedinthecalltoxml_parser_create.</li><li><strong>characterData</strong>:Thisisacallbackreferencetothemethodthatwillbecalledwhencharacterdataisfound.</li></ul><p>Thisfunctionworksinthesamewayasthe<code>xml_set_element_handler()</code>functioninthatitsimplysetsareferencetothefunctionthatwillbecalledwhencharacterdataisencountered.Thefunctioniscalledlikethis.</p><code>xml_set_character_data_handler($xml_parser,"characterData");</code><h4><code>characterData()</code>function</h4><p>The<code>characterData()</code>function,whichagainMUSTbeplacedbeforethecallto<code>xml_set_character_data_handler()</code>andmustalsohavethefollowingparameters.</p><ul><li><strong>xml_parser</strong>:Thereferencetothexmlparsercreatedinthecalltoxml_parser_create.</li><li><strong>data</strong>:ThedataheldwithintheXMLelement.AnyCDATAtagshavebeenusedthentheparserwillreturneverythingbetweenthosetagssononeedtoworryaboutcuttingthemout.</li></ul><p>Sowhentheparserobjectfindsadataobjectthismethodiscalled.Thefollowingfunctionwilljustprintoutthedata.</p><code><pre>functioncharacterData($parser,$data){
echo"Data:".$data."<br/>";
}
</pre></code><p>Onethingthatitisessentialthatyoulookoutforisthefunnythingthattheparserdoeswhenitencounderscertainconditions.Itwillstopparsingandcallthefunctionagain.Thisrepeatsuntilallofthedatahasbeenpassed.I'velisted(Ithink)alloftheconditionsbelow.</p><ul><li>TheparserrunsintoanEntityDeclaration,suchas&(&)or'(')</li><li>Theparserfinishesparsinganentity.</li><li>Theparserrunsintothenew-linecharacter(\n)</li><li>Theparserrunsintoaseriesoftabcharacters(\t)</li><li>Thecontentofthe$dataparameterismorethan1024(bytes).</li></ul><p>Thebestwaytoexplainthisistouseanexample.Letssaythatyouhavethefollowingstringaspartofthedata.</p><code><pre>sometext&
somemoretext'
lastbitoftext
</pre></code><p>Ifyouusedthepreviousexamplemethodofjustprintingouttheinformationthentheparserwillprintoutthefollowing:</p><code><pre>Data:sometext
Data:&
Data:somemoretext
Data:'
Data:lastbitoftext
</pre></code><p>Sobesurethatwhenyoucallthemethodtomakesurethatallofthecharacterdataispassedthrough.Onethingyoucoulddoistohavethe<code>characterData()</code>functionaddthedatatoastring.ThestringisinitialisedwhenthestartElementfunctioniscalledandprintedoffwhentheendElementfunctioniscalled.</p><h3><code>xml_parser_set_option()</code></h3><p>Thismethodisoptionalandcanbeusedifyouwanttheparsertohaveacertainbehaviour.Forexample,toturnoffcasefoldingontheparserusethefollowingcode.</p><code>xml_parser_set_option($xml_parser,XML_OPTION_CASE_FOLDING,false);</code><p>Casefoldingisbasicallytheturningofcharacterstotheiruppercaseequivalent.However,inXMLalltagsmustbelowercasesoandforsomereasonthedefaultoftheparserisforthistobeon.Soifyoucreatew3cvalidXMLmakesurethatyouusethisfunctiontoturnoffcasefolding.Hereisalistoftheavailableoptionsforthisfunction.</p><ul><li><strong>XML_OPTION_CASE_FOLDING</strong>:(integer)Controlswhethercase-foldingisenabledforthisXMLparser.Enabledbydefault.</li><li><strong>XML_OPTION_SKIP_TAGSTART</strong>:(integer)Specifyhowmanycharactersshouldbeskippedinthebeginningofatagname.</li><li><strong>XML_OPTION_SKIP_WHITE</strong>:(integer)Whethertoskipvaluesconsistingofwhitespacecharacters.</li><li><strong>XML_OPTION_TARGET_ENCODING</strong>:(string)SetswhichtargetencodingtouseinthisXMLparser.Bydefault,itissettothesameasthesourceencodingusedby<code>xml_parser_create()</code>.SupportedtargetencodingsareISO-8859-1,US-ASCIIandUTF-8.</li></ul><h3><code>xml_parse()</code></h3><p>Thisfunctionisusedtoruntheparseroversomeinput.Ittakesthefollowingparameters:</p><ul><li><strong>xml_parser</strong>:Thisisaxmlparserobjectcreatedinthe<code>xml_parser_create()</code>function.</li><li><strong>data</strong>:Achunkofdatatoparse.Thiscanbereadfromafileorastream.</li><li><strong>end</strong>:(optional)Ifthisissettotruethenthisisthelastbitofdatafromthesourceandsothisisthelasttimethefunctionwillberun.</li></ul><p>Asyoucanseethe<code>xml_parse()</code>functioncanberunoverandoveragainuntilallofthedatahasbeenreadfromthefile.</p><code><pre>if(!($fp=fopen("an_xmfile.xml","r"))){
die("couldnotopenXMLinput");
}
while($data=fread($fp,4096)){
if (!xml_parse($xml_parser,$data,feof($fp))){
die(sprintf("XMLerror:%satline%d",xml_error_string(xml_get_error_code($xml_parser)),xml_get_current_line_number($xml_parser)));
}
}
</pre></code><h3><code>xml_parser_free()</code></h3><p>AsthenamesuggeststhisfunctioniscalledattheendoftheXMLparsingrun.ItbasicallyjustclearsupthememoryandthrowsawaytheXMLparserobjectcreatedatthestart.</p><h3>Puttingthemalltogether</h3><p>JustasanexampleIhaveputthecodetogetherintosomethingthatwillspitoutXMLintoformattedHTML,albeitalittleugly.ItisdesignedtoallowyoutoexpandupontocreateyourownXMLparsingscript.</p><code><pre>//起始元素功能
functionstartElement($xmlParser,$name,$attribs){
echo"Start:".$name."<br/>";
}
//结束元素功能
functionendElement($parser,$name){
echo"End:".$name."<br/>";
}
functioncharacterData($parser,$data){
echo"Data:".$data."<br/>";
}
$xml_parser=xml_parser_create();
xml_parser_set_option($xml_parser,XML_OPTION_CASE_FOLDING,false);
xml_set_element_handler($xml_parser,"startElement","endElement");
xml_set_character_data_handler($xml_parser,"characterData");
if(!($fp=fopen("an_xml_file.xml","r"))){
die("couldnotopenXMLinput");
}
while($data=fread($fp,4096)){
if(!xml_parse($xml_parser,$data,feof($fp))){
die(sprintf("XMLerror:%satline%d",xml_error_string(xml_get_error_code($xml_parser)),xml_get_current_line_number($xml_parser)));
}
}
</pre></code><p> </p>
