DOMXPath::evaluate

(PHP 5 >= 5.1.0)

DOMXPath::evaluate — Evaluates the given XPath expression and returns a typed result if possible

说明

public mixed DOMXPath::evaluate ( string $expression [, DOMNode $contextnode [, bool $registerNodeNS = true ]] )

Executes the given XPath expression and returns a typed result if possible.

参数

expression: The XPath expression to execute.
contextnode: The optional contextnode can be specified for doing relative XPath queries. By default, the queries are relative to the root element.
registerNodeNS: The optional registerNodeNS can be specified to disable automatic registration of the context node.

返回值

Returns a typed result if possible or a DOMNodeList containing all nodes matching the given XPath expression.

If the expression is malformed or the contextnode is invalid, DOMXPath::evaluate() returns FALSE.

更新日志

版本	说明
5.3.3	The `registerNodeNS` parameter was added.

范例

Example #1 Getting the count of all the english books


<?php

$doc = new DOMDocument;

$doc->load('book.xml');

$xpath = new DOMXPath($doc);

$tbody = $doc->getElementsByTagName('tbody')->item(0);

// our query is relative to the tbody node
$query = 'count(row/entry[. = "en"])';

$entries = $xpath->evaluate($query, $tbody);
echo "There are $entries english books\n";

?>

以上例程会输出：

There are 2 english books

参见

DOMXPath::query() - Evaluates the given XPath expression

PHP手册 - N: Evaluates the given XPath expression and returns a typed result if possible

用户评论:

daniel at danielnorton dot com (26-Jun-2011 05:56)

Note that this method does not provide any means to distinguish between a successful result that returns FALSE and an error. For example, this will succeed and return FALSE: <?php $xpath->evaluate("1 = 0"); ?> One workaround when you know you are expecting a Boolean is to wrap the result with string(). e.g. <?php $xpath->evaluate("string(1 = 0)"); ?> This will return a string "false" on success, or the Boolean FALSE on error.

Damien Bezborodov (29-Mar-2011 02:13)

If your expression returns a node set, you will get a DOMNodeList instead of a typed result. Instead, try modifying your expression from "//node[1]" to "string(//node[1])".

daniel ad demus dk (16-Jun-2008 11:02)

It seems this method is only included from PHP 5.1.

yuriucsal at NOSPAM dot yahoo dot com dot br (06-Mar-2005 08:55)

this class can substitute the method evaluate while it is not validated. Made for Yuri Bastos and Jo?o Gilberto Magalh?es. <?php class XPtahQuery { // function returns a DOMNodeList from a relative xPath public static function selectNodes($pNode, $xPath) { $pos = strpos(self::getFullXpath($pNode),"/",1); $xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste /#document[1]/ $xPathQueryFull = $xPathQuery. $xPath; $domXPath = new DOMXPath($pNode->ownerDocument); $rNodeList = $domXPath->query($xPathQueryFull); return $rNodeList; } // function returns a DOMNode from a xPath from other DOMNode public static function selectSingleNode($pNode, $xPath) { $pos = strpos(self::getFullXpath($pNode),"/",1); $xPathQuery = substr(self::getFullXpath($pNode),$pos);//to paste /#document[1]/ $xPathQueryFull = $xPathQuery. $xPath; $domXPath = new DOMXPath($pNode->ownerDocument); $rNode = $domXPath->query($xPathQueryFull)->item(0); return $rNode; } //utilitaries functions off selectSingleNode private function getNodePos($pNode, $nodeName) { if($pNode == null) { return 0; } else { $var = 0; if ($pNode->previousSibling != null) { if ($pNode->previousSibling->nodeName == $nodeName) { $var = 1; } } return self::getNodePos($pNode->previousSibling, $nodeName) + $var; } } //utilitaries functions off selectSingleNode private function getFullXpath($pNode) { if($pNode == null) { return ""; } else { return self::getFullXpath($pNode->parentNode) . "/" . $pNode->nodeName . "[" .strval(self::getNodePos($pNode, $pNode->nodeName)+1) . "]";//+1 to get the real xPath index } } } ?>