SimpleXMLElement::__construct

(PHP 5, PHP 7)

SimpleXMLElement::__construct — Creates a new SimpleXMLElement object

说明

final public SimpleXMLElement::__construct ( string $data [, int $options = 0 [, bool $data_is_url = FALSE [, string $ns = "" [, bool $is_prefix = FALSE ]]]] )

Creates a new SimpleXMLElement object.

参数

data

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

options

Optionally used to specify additional Libxml parameters.

Note:

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

data_is_url

By default, data_is_url is FALSE. Use TRUE to specify that data is a path or URL to an XML document instead of string data.

ns

Namespace prefix or URI.

is_prefix

TRUE if ns 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();

?>

更新日志

版本 说明
5.2.0 Added the ns and is_prefix parameters.
5.1.2 Added the options and data_is_url parameters.

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.