Implementation code for reading and writing XML DOM with PHP_PHP tutorial

Reading and writing Extensible Markup Language (XML) in PHP can seem a little scary. In fact, XML and all its related technologies can be scary, but reading and writing XML in PHP doesn't have to be a scary task. First, you need to learn a little bit about XML—what it is and what you can do with it. Then, you need to learn how to read and write XML in PHP, and there are many ways to do this.
This article provides a brief introduction to XML and then explains how to read and write XML with PHP.
What is XML?
XML is a data storage format. It does not define what data is saved, nor does it define the format of the data. XML simply defines tags and the attributes of those tags. Well-formed XML tags look like this:
Jack Herrington
This tag contains some text: Jack Herrington.
An XML tag that does not contain text looks like this:

There is more than one way to write something in XML. For example, this tag forms the same output as the previous tag:

You can also add attributes to XML tags. For example, this tag contains first and last attributes:

Special characters can also be encoded in XML. For example, the & symbol can be encoded like this:
&
An XML file containing tags and attributes is well-formed if it is formatted like the example, meaning that the tags are symmetrical and the characters are encoded correctly. Listing 1 is an example of well-formed XML.

Listing 1. XML book list example

Copy code The code is as follows:

Jack Herrington

O'Reilly


Jack Herrington
O'Reilly

The XML in Listing 1 contains a list of books. The parent tag contains a set of tags, each of which contains , /",
$block, $title );
preg_match_all( "/ (.*?)/",
$block, $publisher );
echo( $title[1][0]." - ".$author[1] [0]." - ".
$publisher[1][0]."n" );
}
?>

Please note this How short is the code. Initially, it reads the file into a large string. Then use a regex function to read each book item. Finally, use a foreach loop to loop through each book block and extract the author, title, and publisher.
So, where are the flaws? The problem with using regular expression code to read XML is that it doesn't first check to make sure the XML is well-formed. This means that there is no way to know whether the XML is well-formed before reading it. Also, some well-formed XML may not match the regular expression, so they must be modified later.
I never recommend using regular expressions to read XML, but sometimes it is the most compatible way because the regular expression functions are always available. Do not use regular expressions to read XML directly from the user because you have no control over the format or structure of such XML. You should always use a DOM library or a SAX parser to read XML from the user.
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Writing XML using DOM
Read Fetching the XML is only part of the equation. How to write XML? The best way to write XML is with the DOM. Listing 5 shows how the DOM builds the book XML file.
Listing 5. Writing book XML using DOM

Copy the code The code is as follows:

$books = array();
$books [] = array(
'title' => 'PHP Hacks',
'author' => 'Jack Herrington',
'publisher ' => "O'Reilly"
);
$books [] = array(
'title' => 'Podcasting Hacks',
'author' => 'Jack Herrington ',
'publisher' => "O'Reilly"
);
$doc = new DOMDocument();
$doc->formatOutput = true;
$r = $doc->createElement( "books" );
$doc->appendChild( $r );
foreach( $books as $book )
{
$b = $doc- >createElement( "book" );
$author = $doc->createElement( "author" );
$author->appendChild(
$doc->createTextNode( $book[ 'author'] )
);
$b->appendChild( $author );
$title = $doc->createElement( "title" );
$title-> appendChild(
$doc->createTextNode( $book['title'] )
);
$b->appendChild( $title );
$publisher = $doc-> createElement( "publisher" );
$publisher->appendChild(
$doc->createTextNode( $book['publisher'] )
);
$b->appendChild( $publisher );
$r->appendChild( $b );
}
echo $doc->saveXML();
?>

At the top of the script, the books array is loaded with some example books. This data can come from the user or from the database.
After the sample book is loaded, the script creates a new DOMDocument and adds the root node books to it. The script then creates nodes for each book's author, title, and publisher, and adds a text node for each node. The final step for each book node is to re-add it to the root books node.
At the end of the script, use the saveXML method to output XML to the console. (You can also use the save method to create an XML file.) The output of the script is shown in Listing 6.
Listing 6. Output of DOM build script

Copy the code The code is as follows:

php e4.php



Jack Herrington

O'Reilly

The real value of using DOM is that the XML it creates is always well-formed. But what if you can't create XML with the DOM?
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Writing XML with PHP
If DOM is not available, XML can be written using PHP's text template. Listing 7 shows how PHP builds the book XML file.
Listing 7. Writing book XML in PHP

Copy the code The code is as follows:

$books = array();
$books [] = array(
'title' => 'PHP Hacks',
'author' => 'Jack Herrington',
'publisher ' => "O'Reilly"
);
$books [] = array(
'title' => 'Podcasting Hacks',
'author' => 'Jack Herrington ',
'publisher' => "O'Reilly"
);
?>

foreach( $books as $ book )
{
?>







}
?>

The top part of the script is similar to the DOM script. The bottom of the script opens the books tag and then iterates through each book, creating the book tag and all the inner title, author, and publisher tags.
The problem with this approach is encoding the entities. To ensure that entities are encoded correctly, the htmlentities function must be called on each item, as shown in Listing 8.
Listing 8. Encoding entities using the htmlentities function

Copy the code The code is as follows:

foreach( $books as $book )
{
$title = htmlentities( $book['title'], ENT_QUOTES );
$author = htmlentities( $book[ 'author'], ENT_QUOTES );
$publisher = htmlentities( $book['publisher'], ENT_QUOTES );
?>






}
?>

This is the annoying thing about writing XML in basic PHP. You think you've created perfect XML, but as soon as you try to use the data, you discover that some elements are encoded incorrectly.
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Conclusion
There is a lot of exaggeration and confusion surrounding XML place. However, it’s not as difficult as you think – especially in a language as great as PHP. Once you understand and implement XML correctly, you'll find many powerful tools at your disposal. XPath and XSLT are two such tools worth investigating.

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