SimpleXMLElement::__construct

(PHP 5, PHP 7, PHP 8)

SimpleXMLElement::__construct — Creates a new SimpleXMLElement object

说明

public SimpleXMLElement::__construct ( string $data , int $options = 0 , bool $dataIsURL = false , string $namespaceOrPrefix = "" , bool $isPrefix = false )

Creates a new SimpleXMLElement object.

参数

data

A well-formed XML string or the path or URL to an XML document if dataIsURL is true.

options

Optionally used to specify additional Libxml parameters, which affect reading of XML documents. Options which affect the output of XML documents (e.g. LIBXML_NOEMPTYTAG) are silently ignored.

Note:

It may be necessary to pass LIBXML_PARSEHUGE to be able to process deeply nested XML or very large text nodes.

dataIsURL

By default, dataIsURL is false. Use true to specify that data is a path or URL to an XML document instead of string data.

namespaceOrPrefix

Namespace prefix or URI.

isPrefix

true if namespaceOrPrefix is a prefix, false if it's a URI; defaults to false.

返回值

Returns a SimpleXMLElement object representing data.

错误／异常

Produces an E_WARNING error message for each error found in the XML data and additionally throws an Exception if the XML data could not be parsed.

Tip

Use libxml_use_internal_errors() to suppress all XML errors, and libxml_get_errors() to iterate over them afterwards.

范例

Note:

Listed examples may include example.php, which refers to the XML string found in the first example of the basic usage guide.

Example #1 Create a SimpleXMLElement object

<?php

include 'example.php';

$sxe = new SimpleXMLElement($xmlstr);
echo $sxe->movie[0]->title;

?>

以上例程会输出：

PHP: Behind the Parser

Example #2 Create a SimpleXMLElement object from a URL

<?php

$sxe = new SimpleXMLElement('http://example.org/document.xml', NULL, TRUE);
echo $sxe->asXML();

?>

参见

User Contributed Notes

rowan dot collins at gmail dot com 22-Apr-2017 03:23
The manual doesn't really explain what the $ns argument (and the accompanying $is_prefix) are for.

What they do is similar to the ->children() method: they set the context of the returned object to that namespace, so that access via ->elementName and ['attributeName'] refer to elements and attributes in that namespace.

In particular, they do *not* change the namespaces which exist on the document.

See this example:

<?php
// This XML contains two elements called <child>
// One is in the namespace http://example.com, with local prefix 'ws'
// The other has no namespace (no prefix, and no default namespace declared)
$xml = '<ws:example xmlns:ws="http://example.com"><child>Not in namespace</child><ws:child>In example namespace</ws:child></ws:example>';

$sx0 = new SimpleXMLElement($xml, 0, false);
$sx1 = new SimpleXMLElement($xml, 0, false, 'http://example.com');
$sx2 = new SimpleXMLElement($xml, 0, false, 'ws', true);

echo "
    Without: {$sx0->child}
    By namespace: {$sx1->child}
    By prefix: {$sx2->child}
";
?>

Output:

 Without: Not in namespace
 By namespace: In example namespace
 By prefix: In example namespace
ahmad dot mayahi at gmail dot com 07-Jun-2016 09:36
You won't be able to load an XML file without root element:

//This will throw an exception
$xml = new SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?>', null, false);

//Here is the solution
$xml = new SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?><root></root>', null, false);
Phil Cross 01-Sep-2014 11:39
It's worth noting, that you need to typecast dynamic property names to string in order to retrieve there value, for example:

<?php
    $xml = new SimpleXMLElement('records.xml', 0, true);

    // This will work as expected because its a hard coded property value
    foreach($xml as $record){
        echo $record->id;    // Will output the ID fine
    }

    // Dynamic properties require typecasting to string
    $xml_field = 'id';
    foreach($xml as $record){

        // This will dump a SimpleXMLElement object
        var_dump($record->$xml_field);

        // This will output the value as expected
        echo (string)$record->$xml_field;
    }
?>
bertolini dot cedric at me dot com 16-Jun-2014 11:07
It's worth noting that the behavior of SimpleXmlElement::__construct is not exactly the same as simplexml_load_string, regarding libxml_use_internal_errors().

In my case,

<?php
libxml_use_internal_errors(true);
new \SimpleXmlElement($data);
?>

was still throwing error. But as soon as I switched to

<?php
libxml_use_internal_errors(true);
simplexml_load_string($data);
?>

everything worked fine and I stopped getting an error.
kumarldh at gmail dot com 22-Mar-2011 10:50
Using libxml_use_internal_errors() may suppress errors but Exception still requires decent handling. I used following code snippet.

<?php
libxml_use_internal_errors(true);
try{
    $xmlToObject = new SimpleXMLElement($notSoWellFormedXML);
} catch (Exception $e){
    echo 'Please try again later...';
    exit();
}
?>
uramihsayibok, gmail, com 16-Aug-2009 06:52
As I was filling out a bug report, I realized why (speculation here) the constructor is final: so that functions like simplexml_load_file and simplexml_load_string can work. I imagine the PHP-ized code looks something like

<?php

function simplexml_load_file($filename, $class_name = "SimpleXMLElement", $options = 0, $ns = "", $is_prefix = false) {
    return new $class_name($filename, $options, true, $ns, $is_prefix);
}

?>

If we were to use a different $class_name and change the constructor's definition these functions wouldn't work.

There's no easy, sensible solution that keeps simplexml_load_file and simplexml_load_string.
tudor at culise dot net 20-Nov-2007 03:35
This class is extendable, but it's too bad that its constructor cannot be overriden (PHP says it's a final method). Thus the class should be wrapped using the delegation principle rather that extended.