PHP | XMLReader isValid() Function

The XMLReader::isValid() function is an inbuilt function in PHP which is used to check if the document being parsed is valid or not. An XML is valid if it is written by following a DTD (Document Type Definition) which defines all the allowed elements and the structure of elements.

Syntax:

bool XMLReader::isValid( void )

Parameters: This function doesn’t accepts any parameter.



Return Value: This function returns TRUE on success or FALSE on failure.

Below given programs illustrate the XMLReader::isValid() function in PHP:

Program 1:
Filename: data.xml

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<?xml version="1.0"?>
<!-- DTD rules to be followed by XML-->
<!DOCTYPE html [
<!ELEMENT html (h1, p, heading, body)>
<!ELEMENT h1 (#PCDATA)>
<!ELEMENT p (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
  
<!-- XML starts from here -->
<html>
<h1>Hi</h1>
<p>World</p>
<heading>GeeksforGeeks</heading>
<body>Web Portal for Geeks</body>
</html>

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Filename: index.php

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<?php
  
// Create a new XMLReader instance
$XMLReader = new XMLReader();
  
// Open the XML file
$XMLReader->open('data.xml');
  
// Enable the Parser Property
$XMLReader->setParserProperty(
       XMLReader::VALIDATE, true);
  
// Iterate through the XML nodes
while ($XMLReader->read()) {
    if ($XMLReader->nodeType == XMLREADER::ELEMENT) {
  
        // Check if XML is valid or not
        $isValid = $XMLReader->isValid();
        if ($isValid) {
            echo "YES ! this node is validated<br>";
        }
    }
}
?>

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Output:

YES ! this node is validated
YES ! this node is validated
YES ! this node is validated
YES ! this node is validated
YES ! this node is validated

Program 2:
Filename: data.xml

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<?xml version="1.0"?>
<!-- DTD rules to be followed by XML-->
<!DOCTYPE html [
<!ELEMENT html (heading, body)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
<!-- XML starts from here -->
<html>
<body>Web Portal for Geeks</body>
</html>

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Filename: index.php

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<?php
  
// Create a new XMLReader instance
$XMLReader = new XMLReader();
  
// Open the XML file
$XMLReader->open('data.xml');
  
// Enable the Parser Property
$XMLReader->setParserProperty(
         XMLReader::VALIDATE, true);
  
// Iterate through the XML nodes
while ($XMLReader->read()) {
    if ($XMLReader->nodeType == XMLREADER::ELEMENT) {
  
        // Check if XML is valid or not
        $isValid = $XMLReader->isValid();
        if (!$isValid) {
            echo "No ! this node is not validated<br>";
        }
    }
}
?>

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Output:

No ! this node is not validated
No ! this node is not validated

Reference: https://www.php.net/manual/en/xmlreader.isvalid.php




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