DOMXPath::evaluate

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

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

说明

public DOMXPath::evaluate(string $expression, ?DOMNode $contextNode = null, bool $registerNodeNS = true): mixed

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

Whether to automatically register the in-scope namespace prefixes of the context node to the DOMXPath object. This can be used to avoid needing to call DOMXPath::registerNamespace() manually for each in-scope namespaces. When a namespace prefix conflict exists, only the nearest descendant namespace prefix is registered.

错误／异常

The following errors are possible when using an expression that invokes PHP callbacks.

  • Throws an Error if a PHP callback is invoked but there were no callbacks registered, or if the named callback was not registered.
  • Throws a TypeError if the php:function syntax is used and the handler name is not a string.
  • Throws an Error if a non-DOM object was returned from a callback.

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.

示例

示例 #1 Getting the count of all the english books

<?php

$doc = new DOMDocument;

$doc->load('examples/book-dcobook.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";

?>

以上示例会输出：

There are 2 english books

参见