View source for XML validation

{{draft task}}

Given an XML document and an XSD schema definition validate that the document follows the schema described. 

Sample XML and XSD for tests can be found on [https://www.w3schools.com/xml/schema_example.asp this W3 Schools page].

=={{header|C}}==
{{libheader|LibXML}}
At the time of writing, the XML and XSD files at the URLs used in the other examples were inaccessible. The files from the W3 Schools page were used for tests.
<syntaxhighlight lang="c">
#include <libxml/xmlschemastypes.h>

int main(int argC, char** argV)
{
	if (argC <= 2) {
		printf("Usage: %s <XML Document Name> <XSD Document Name>\n", argV[0]);
		return 0;
	}
	
	xmlDocPtr doc;
	xmlSchemaPtr schema = NULL;
	xmlSchemaParserCtxtPtr ctxt;
	char *XMLFileName = argV[1];
	char *XSDFileName = argV[2];
	int ret;

	xmlLineNumbersDefault(1);

	ctxt = xmlSchemaNewParserCtxt(XSDFileName);

	xmlSchemaSetParserErrors(ctxt, (xmlSchemaValidityErrorFunc) fprintf, (xmlSchemaValidityWarningFunc) fprintf, stderr);
	schema = xmlSchemaParse(ctxt);
	xmlSchemaFreeParserCtxt(ctxt);


	doc = xmlReadFile(XMLFileName, NULL, 0);

	if (doc == NULL){
		fprintf(stderr, "Could not parse %s\n", XMLFileName);
	}
	else{
		xmlSchemaValidCtxtPtr ctxt;

		ctxt = xmlSchemaNewValidCtxt(schema);
		xmlSchemaSetValidErrors(ctxt, (xmlSchemaValidityErrorFunc) fprintf, (xmlSchemaValidityWarningFunc) fprintf, stderr);
		ret = xmlSchemaValidateDoc(ctxt, doc);
		
		if (ret == 0){
			printf("%s validates\n", XMLFileName);
		}
		else if (ret > 0){
			printf("%s fails to validate\n", XMLFileName);
		}
		else{
			printf("%s validation generated an internal error\n", XMLFileName);
		}
		xmlSchemaFreeValidCtxt(ctxt);
		xmlFreeDoc(doc);
	}


	if(schema != NULL)
		xmlSchemaFree(schema);

	xmlSchemaCleanupTypes();
	xmlCleanupParser();
	xmlMemoryDump();

	return 0;
}
</syntaxhighlight>
Output, files used from the W3 Schools page :
<pre>
C:\rosettaCode>xmlValidator.exe shiporder.xml shiporder.xsd
shiporder.xml validates
</pre>

=={{header|C sharp}}==
<syntaxhighlight lang="csharp">
using System;
using System.Xml;
using System.Xml.Schema;
using System.IO;

public class Test
{
	public static void Main()
	{
		// your code goes here
		XmlSchemaSet sc = new XmlSchemaSet();
		sc.Add(null, "http://venus.eas.asu.edu/WSRepository/xml/Courses.xsd");
		XmlReaderSettings settings = new XmlReaderSettings();
		settings.ValidationType = ValidationType.Schema;
		settings.Schemas = sc;
		settings.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);
		// Create the XmlReader object.
		XmlReader reader = XmlReader.Create("http://venus.eas.asu.edu/WSRepository/xml/Courses.xml", settings);
		// Parse the file.
		while (reader.Read()); 
		// will call event handler if invalid
		Console.WriteLine("The XML file is valid for the given xsd file");
	}
	
	// Display any validation errors.
	private static void ValidationCallBack(object sender, ValidationEventArgs e) {
		Console.WriteLine("Validation Error: {0}", e.Message);
	}
}
</syntaxhighlight>

=={{header|FreeBASIC}}==
{{libheader|libxml2}}
<syntaxhighlight lang="vbnet">#include once "crt/stdio.bi"
#include once "crt/stdlib.bi"
#include once "libxml/tree.bi"
#include once "libxml/parser.bi"

'' Load the XML document
dim as xmlDocPtr doc = xmlReadFile("document.xml", NULL, 0)
if doc = NULL then
    print "Error opening XML document."
    end 1
end if

'' Load the XSD schema
dim as xmlSchemaParserCtxtPtr ctxt = xmlSchemaNewParserCtxt("schema.xsd")
if ctxt = NULL then
    print "Error opening XSD schema."
    xmlFreeDoc(doc)
    end 1
end if

'' Parse the XSD schema
dim as xmlSchemaPtr schema = xmlSchemaParse(ctxt)
if schema = NULL then
    print "Error parsing XSD schema."
    xmlSchemaFreeParserCtxt(ctxt)
    xmlFreeDoc(doc)
    end 1
end if

'' Create a validation context
dim as xmlSchemaValidCtxtPtr vctxt = xmlSchemaNewValidCtxt(schema)
if vctxt = NULL then
    print "Error creating validation context."
    xmlSchemaFree(schema)
    xmlSchemaFreeParserCtxt(ctxt)
    xmlFreeDoc(doc)
    end 1
end if

'' Validate the XML document against the XSD schema
if xmlSchemaValidateDoc(vctxt, doc) = 0 then
    print "The XML document is valid according to the XSD schema."
else
    print "The XML document is not valid according to the XSD schema."
end if

'' Free resources
xmlSchemaFreeValidCtxt(vctxt)
xmlSchemaFree(schema)
xmlSchemaFreeParserCtxt(ctxt)
xmlFreeDoc(doc)
xmlCleanupParser()</syntaxhighlight>

=={{header|F_Sharp|F#}}==
<p>Using an inline stylesheet:</p>
<syntaxhighlight lang="fsharp">open System.Xml
open System.Xml.Schema
open System.IO

let xml = @"<root>
<!--Start of schema-->
<xs:schema id='an-element' targetNamespace='example' xmlns:mstns='example' xmlns='example' xmlns:xs='http://www.w3.org/2001/XMLSchema' attributeFormDefault='unqualified' elementFormDefault='qualified'>
  <xs:element name='an-element'>
    <xs:complexType>
      <xs:sequence minOccurs='0' maxOccurs='unbounded'>
        <xs:element name='another-element' nillable='true'>
          <xs:complexType>
            <xs:simpleContent>
              <xs:extension base='xs:string'>
                <xs:attribute name='an-attribute' form='unqualified' type='xs:boolean' />
              </xs:extension>
            </xs:simpleContent>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>
<!--End of schema-->
<an-element xmlns='example'>
    <another-element an-attribute='false'>...</another-element>
    <another-element an-attribute='wrong'>123</another-element>
</an-element>
</root>"

let validationData withWarnings =
    let errors = ref 0
    let warnings = ref 0
    fun input ->
        match input with
        | Some(msg, severity) ->
            if severity = XmlSeverityType.Error then
                errors := !errors + 1
                printfn "Validation error: %s" msg
            elif withWarnings then
                warnings := !warnings + 1
                printfn "Validation warning: %s" msg
            None
        | None ->
            if withWarnings then
                Some(dict[XmlSeverityType.Error, !errors; XmlSeverityType.Warning, !warnings])
            else
                Some(dict[XmlSeverityType.Error, !errors])

[<EntryPoint>]
let main argv =
    let withWarnings = argv.Length > 0 && argv.[0] = "-w"
    let vData = validationData withWarnings
    let validationEvent = new ValidationEventHandler(fun _ e ->
        vData (Some(e.Message, e.Severity)) |> ignore)
    let settings = new XmlReaderSettings()
    settings.ValidationType <- ValidationType.Schema
    settings.ValidationEventHandler.AddHandler(validationEvent)
    settings.ValidationFlags <- settings.ValidationFlags ||| XmlSchemaValidationFlags.ProcessInlineSchema ||| XmlSchemaValidationFlags.ReportValidationWarnings
    let reader = XmlReader.Create(new StringReader(xml), settings);
    while reader.Read() do ()
    printfn "%A" (Seq.toList (vData None).Value)
    0
</syntaxhighlight>
{{out}}
<pre style="white-space:pre-wrap">>RosettaCode
Validation error: The 'an-attribute' element is invalid - The value 'wrong' is invalid according to its datatype 'http://www.w3.org/2001/XMLSchema:boolean' - The string 'wrong' is not a valid boolean value.
[[Error, 1]]

>RosettaCode -w
Validation warning: Could not find schema information for the element 'root'.
Validation error: The 'an-attribute' element is invalid - The value 'wrong' is invalid according to its datatype 'http://www.w3.org/2001/XMLSchema:boolean' - The string 'wrong' is not a valid boolean value.
[[Error, 1]; [Warning, 1]]

</pre>
<p>Changing <code>wrong</code> to a boolean, e. g. <code>true</code>, The result (without -w) is <pre>[[Error, 0]]</pre>

=={{header|FutureBasic}}==
FB has native XML validators.
<syntaxhighlight lang="futurebasic">
include "NSLog.incl"
include "Tlbx XML.incl"

// Sample XML courtesy https://www.w3schools.com/xml/schema_example.asp
local fn Sample1XMLDocument as CFStringRef
  CFStringRef xmlDoc = @"<?xml version=\"1.0\" encoding=\"UTF-8\" ?>\n¬
  <xs:schema xmlns:xs=\"http://www.w3.org/2001/XMLSchema\">\n¬
  <xs:element name=\"shiporder\">\n¬
  <xs:complexType>\n¬
  <xs:sequence>\n¬
  <xs:element name=\"orderperson\" type=\"xs:string\"/>\n¬
  <xs:element name=\"shipto\">\n¬
  <xs:complexType>\n¬
  <xs:sequence>\n¬
  <xs:element name=\"name\" type=\"xs:string\"/>\n¬
  <xs:element name=\"address\" type=\"xs:string\"/>\n¬
  <xs:element name=\"city\" type=\"xs:string\"/>\n¬
  <xs:element name=\"country\" type=\"xs:string\"/>\n¬
  </xs:sequence>\n¬
  </xs:complexType>\n¬
  </xs:element>\n¬
  <xs:element name=\"item\" maxOccurs=\"unbounded\">\n¬
  <xs:complexType>\n¬
  <xs:sequence>\n¬
  <xs:element name=\"title\" type=\"xs:string\"/>\n¬
  <xs:element name=\"note\" type=\"xs:string\" minOccurs=\"0\"/>\n¬
  <xs:element name=\"quantity\" type=\"xs:positiveInteger\"/>\n¬
  <xs:element name=\"price\" type=\"xs:decimal\"/>\n¬
  </xs:sequence>\n¬
  </xs:complexType>\n¬
  </xs:element>\n¬
  </xs:sequence>\n¬
  <xs:attribute name=\"orderid\" type=\"xs:string\" use=\"required\"/>\n¬
  </xs:complexType>\n¬
  </xs:element>\n¬
  </xs:schema>"
end fn = xmlDoc

local fn ValidateXML( string as CFStringRef ) as BOOL
  ErrorRef          err = NULL
  XMLDocumentRef xmlDoc = fn XMLDocumentWithXMLString( string, NSXMLDocumentValidate + NSXMLNodePreserveAll, err )
  if err then NSLog( @"Error: %@", fn ErrorLocalizedDescription( err ) ) : exit fn
  BOOL         validXML = fn XMLDocumentValidate( xmlDoc, err )
  if err then NSLog( @"Error: %@", fn ErrorLocalizedDescription( err ) ) else exit fn = validXML
end fn = NO

CFStringRef xmlDoc, xmlName
BOOL        success

xmlDoc  = fn Sample1XMLDocument
success = fn ValidateXML( xmlDoc )
xmlName = @"XML Sample No. 1"
if success then NSLog( @"%@: XML document is valid.\n", xmlName ) else NSLog( @"%@ XML document is invalid.\n", xmlName )

HandleEvents
</syntaxhighlight>
{{output}}
<pre>
XML Sample No. 1: XML document is valid.
</pre>

=={{header|Go}}==
{{libheader|libxml2(Go)}}
<br>
This uses the w3schools test data linked to above.
<syntaxhighlight lang="go">package main

import (
    "fmt"
    "github.com/lestrrat-go/libxml2"
    "github.com/lestrrat-go/libxml2/xsd"
    "io/ioutil"
    "log"
    "os"
)

func check(err error) {
    if err != nil {
        log.Fatal(err)
    }
}

func main() {
    xsdfile := "shiporder.xsd"
    f, err := os.Open(xsdfile)
    check(err)
    defer f.Close()

    buf, err := ioutil.ReadAll(f)
    check(err)

    s, err := xsd.Parse(buf)
    check(err)
    defer s.Free()

    xmlfile := "shiporder.xml"
    f2, err := os.Open(xmlfile)
    check(err)
    defer f2.Close()

    buf2, err := ioutil.ReadAll(f2)
    check(err)

    d, err := libxml2.Parse(buf2)
    check(err)

    if err := s.Validate(d); err != nil {
        for _, e := range err.(xsd.SchemaValidationError).Errors() {
            log.Printf("error: %s", e.Error())
        }
        return
    }

    fmt.Println("Validation of", xmlfile, "against", xsdfile, "successful!")
}</syntaxhighlight>

{{out}}
<pre>
Validation of shiporder.xml against shiporder.xsd successful!
</pre>

=={{header|Groovy}}==
{{trans|Java}}

Solution:
<syntaxhighlight lang="groovy">import static javax.xml.XMLConstants.W3C_XML_SCHEMA_NS_URI
import javax.xml.transform.stream.StreamSource
import javax.xml.validation.SchemaFactory
import org.xml.sax.SAXParseException

def factory = SchemaFactory.newInstance(W3C_XML_SCHEMA_NS_URI)
def validate = { schemaURL, docURL ->
    try {
        factory.newSchema(schemaURL.toURL()).newValidator().validate(new StreamSource(docURL))
        true
    } catch (SAXParseException e) {
        false
    }
}</syntaxhighlight>

Test:
<syntaxhighlight lang="groovy">def schemaLoc = "http://venus.eas.asu.edu/WSRepository/xml/Courses.xsd"
def docLoc = "http://venus.eas.asu.edu/WSRepository/xml/Courses.xml"
println "Document is ${validate(schemaLoc, docLoc)? 'valid' : 'invalid'}"</syntaxhighlight>

=={{header|Java}}==
<syntaxhighlight lang="java">import static javax.xml.XMLConstants.W3C_XML_SCHEMA_NS_URI;

import java.net.MalformedURLException;
import java.net.URL;

import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;
import javax.xml.ws.Holder;

import org.xml.sax.ErrorHandler;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

public class XmlValidation {
	public static void main(String... args) throws MalformedURLException {
		URL schemaLocation = new URL("http://venus.eas.asu.edu/WSRepository/xml/Courses.xsd");
		URL documentLocation = new URL("http://venus.eas.asu.edu/WSRepository/xml/Courses.xml");
		if (validate(schemaLocation, documentLocation)) {
			System.out.println("document is valid");
		} else {
			System.out.println("document is invalid");
		}
	}

	// The least code you need for validation
	public static boolean minimalValidate(URL schemaLocation, URL documentLocation) {
		SchemaFactory factory = SchemaFactory.newInstance(W3C_XML_SCHEMA_NS_URI);
		try {
			Validator validator = factory.newSchema(schemaLocation).newValidator();
			validator.validate(new StreamSource(documentLocation.toString()));
			return true;
		} catch (Exception e) {
			return false;
		}
	}

	// A more complete validator
	public static boolean validate(URL schemaLocation, URL documentLocation) {
		SchemaFactory factory = SchemaFactory.newInstance(W3C_XML_SCHEMA_NS_URI);
		final Holder<Boolean> valid = new Holder<>(true);
		try {
			Validator validator = factory.newSchema(schemaLocation).newValidator();
			// Get some better diagnostics out
			validator.setErrorHandler(new ErrorHandler(){
				@Override
				public void warning(SAXParseException exception) {
					System.out.println("warning: " + exception.getMessage());
				}

				@Override
				public void error(SAXParseException exception) {
					System.out.println("error: " + exception.getMessage());
					valid.value = false;
				}

				@Override
				public void fatalError(SAXParseException exception) throws SAXException {
					System.out.println("fatal error: " + exception.getMessage());
					throw exception;
				}});
			validator.validate(new StreamSource(documentLocation.toString()));
			return valid.value;
		} catch (SAXException e) {
			// Already reported above
			return false;
		} catch (Exception e) {
			// If this is the only thing that throws, it's a gross error
			System.err.println(e);
			return false;
		}
	}
}</syntaxhighlight>

=={{header|Julia}}==
<syntaxhighlight lang="julia">using LightXML

const Xptr = LightXML.Xptr

function validate(url::String, schemafile::String)
    ctxt = ccall((:xmlSchemaNewParserCtxt, LightXML.libxml2), Xptr, (Cstring,), schemafile)
    ctxt != C_NULL || throw(LightXML.XMLNoRootError())
    schema = ccall((:xmlSchemaParse, LightXML.libxml2), Xptr, (Xptr,), ctxt)
    schema != C_NULL || throw(LightXML.XMLNoRootError())
    ccall((:xmlSchemaFreeParserCtxt, LightXML.libxml2), Cvoid, (Xptr,), ctxt)
    ctxt = ccall((:xmlSchemaNewValidCtxt, LightXML.libxml2), Xptr, (Xptr,), schema)
    err = ccall((:xmlSchemaValidateFile, LightXML.libxml2), 
        Cint, (Ptr{LightXML.xmlBuffer}, Cstring), ctxt, url)
    return err == 0 ? true : false
end

function xsdvalidatexml()
    if length(ARGS) != 2
        println("		Usage: julia ", PROGRAM_FILE, ", xmlfilename xsdfilename")
    elseif validate(ARGS[1], ARGS[2])
        println("File ", ARGS[1], " validates as correct XML using the XSD file ", ARGS[2], ".")
    else
        println("File ", ARGS[1]. "does not validate.")
    end
end

xsdvalidatexml()
</syntaxhighlight>

=={{header|Kotlin}}==
{{trans|C}}
{{libheader|libxml2}}
{{works with|Ubuntu 14.04}}
Assuming that libxml2 is already installed on your system in the default location(s), you first need to build libxml_schemas.klib using the following .def file and the cinterop tool:
<pre>
// libxml_schemas.def
headers = /usr/include/libxml2/libxml/xmlschemastypes.h
compilerOpts = -I/usr/include/libxml2
linkerOpts = -L/usr/lib/x86_64-linux-gnu -lxml2
</pre>
Next, you need to compile the following Kotlin program, linking against libxml_schemas.klib. 
<syntaxhighlight lang="scala">// Kotlin Native v0.6

import kotlinx.cinterop.*
import platform.posix.*
import libxml_schemas.*

fun err(ctx: COpaquePointer?, msg: CPointer<ByteVar>?, extra: CPointer<ByteVar>?) {
    val fp = ctx?.reinterpret<FILE>()
    fprintf(fp, msg?.toKString(), extra?.toKString())
}

fun warn(ctx: COpaquePointer?, msg: CPointer<ByteVar>?, extra: CPointer<ByteVar>?) {
    err(ctx, msg, extra)
}

fun main(args: Array<String>) {
    if (args.size != 2) {
        println("You need to pass exactly 2 command line arguments, namely:")
        println("    <XML Document Name> <XSD Document Name>")
        return
    }

    val xmlFileName = args[0]
    val xsdFileName = args[1]
    xmlLineNumbersDefault(1)
    val ctxt = xmlSchemaNewParserCtxt(xsdFileName)

    xmlSchemaSetParserErrors(
        ctxt,
        staticCFunction(::err) as xmlSchemaValidityErrorFunc?,
        staticCFunction(::warn) as xmlSchemaValidityWarningFunc?,
        stderr
    )

    val schema = xmlSchemaParse(ctxt)
    xmlSchemaFreeParserCtxt(ctxt)

    val doc = xmlReadFile(xmlFileName, null, 0)
    if (doc == null) {
        println("Could not parse $xmlFileName")
    }
    else {
        val ctxt2 = xmlSchemaNewValidCtxt(schema)

        xmlSchemaSetValidErrors(
            ctxt2,
            staticCFunction(::err) as xmlSchemaValidityErrorFunc?,
            staticCFunction(::warn) as xmlSchemaValidityWarningFunc?,
            stderr
        )

        val ret = xmlSchemaValidateDoc(ctxt2, doc)
        if (ret == 0)
            println("$xmlFileName validates")
        else if (ret > 0)
            println("$xmlFileName fails to validate")
        else
            println("$xmlFileName generated an internal error")
        xmlSchemaFreeValidCtxt(ctxt2)
        xmlFreeDoc(doc)
    }

    if (schema != null) xmlSchemaFree(schema)
    xmlSchemaCleanupTypes()
    xmlCleanupParser()
    xmlMemoryDump()
}</syntaxhighlight>
Finally, the resulting .kexe file should be executed passing it similar command line arguments to the C entry to produce the following output.
<pre>
$ ./xmlval.kexe shiporder.xml shiporder.xsd
shiporder.xml validates
</pre>

=={{header|Nim}}==
{{libheader|libxml2}}
As in the C version, we use “libxml2” for the validation. As there is no Nim binding for this library, we provide the necessary definitions in our program (three types and six procedures). There is nothing more to do. In Nim, interfacing with C is often very easy.

Our program is based on the C version with many differences. In particular, we use the function “xmlSchemaValidateFile” rather than the function “xmlSchemaValidateDoc”.

<syntaxhighlight lang="nim">import os, strformat

const LibXml = "libxml2.so"

type
  XmlSchemaParserCtxtPtr = pointer
  XmlSchemaPtr = pointer
  XmlSchemaValidCtxtPtr = pointer


# Declaration of needed "libxml2" procedures.

proc xmlSchemaNewParserCtxt(url: cstring): XmlSchemaParserCtxtPtr
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaNewParserCtxt".}

proc xmlSchemaParse(ctxt: XmlSchemaParserCtxtPtr): XmlSchemaPtr
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaParse".}

proc xmlSchemaFreeParserCtxt(ctxt: XmlSchemaParserCtxtPtr)
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaFreeParserCtxt".}

proc xmlSchemaNewValidCtxt(schema: XmlSchemaPtr): XmlSchemaValidCtxtPtr
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaNewValidCtxt".}

proc xmlSchemaValidateFile(ctxt: XmlSchemaValidCtxtPtr; filename: cstring; options: cint): cint
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaValidateFile".}

proc xmlSchemaFreeValidCtxt(ctxt: XmlSchemaValidCtxtPtr)
  {.cdecl, dynlib: LibXml, importc: "xmlSchemaFreeValidCtxt".}


if paramCount() != 2:
  quit &"Usage: {getAppFilename().lastPathPart} <XML Document Name> <XSD Document Name", QuitFailure

let xmlFilename = paramStr(1)
let xsdFilename = paramStr(2)

# Parse XML schema file.
let parserCtxt = xmlSchemaNewParserCtxt(xsdFilename)
let schema = parserCtxt.xmlSchemaParse()
parserCtxt.xmlSchemaFreeParserCtxt()

# Validate XML file using XML schema.
let validCtxt = schema.xmlSchemaNewValidCtxt()
case validCtxt.xmlSchemaValidateFile(xmlFilename, 0)
of 0:
  echo &"“{xmlFilename}” validates."
of -1:
  echo &"“{xmlFilename}” validation generated an internal error."
else:
  echo &"“{xmlFilename}” fails to validate."
validCtxt.xmlSchemaFreeValidCtxt()</syntaxhighlight>

{{out}}
Using command <code>./xml_validate shiporder.xml shiporder.xsd</code>:
<pre>“shiporder.xml” validates.</pre>
Using a modified file “shiporder1.xml” where tag “orderperson” has been replaced by “orderperson1”:
<pre>Entity: line 6: Schemas validity error : Element 'orderperson1': This element is not expected. Expected is ( orderperson ).
“shiporder1.xml” fails to validate.</pre>

=={{header|Perl}}==

<syntaxhighlight lang="perl">#!/usr/bin/env perl -T
use 5.018_002;
use warnings;
use Try::Tiny;
use XML::LibXML;

our $VERSION = 1.000_000;

my $parser = XML::LibXML->new();

my $good_xml         = '<a>5</a>';
my $bad_xml          = '<a>5<b>foobar</b></a>';
my $xmlschema_markup = <<'END';
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="a" type="xsd:integer"/>
</xsd:schema>
END

my $xmlschema = XML::LibXML::Schema->new( string => $xmlschema_markup );

for ( $good_xml, $bad_xml ) {
    my $doc = $parser->parse_string($_);
    try {
        $xmlschema->validate($doc);
    }
    finally {
        if (@_) {
            say "Not valid: @_";
        }
        else {
            say 'Valid';
        }
    };
}</syntaxhighlight>

{{out}}
<pre>Valid
Not valid: unknown-7fe99976a9a0:0: Schemas validity error :
  Element 'a': Element content is not allowed, because the type definition is simple.</pre>

=={{header|Phix}}==
{{trans|C}}
Note that error handling has been delegated to within libxml.e, specifically 
xmlSchemaNewParserCtxt() and xmlSchemaNewValidCtxt() assign an internal handler,
which resorts to xmlGetLastError() and therefore needs to use a bit of cffi, 
that is rather than using the (odd-looking) error it is actually passed.
The libxml.e wrapper was penned specifically for this task and is just about as
bare-bones as it could ever possibly be, and win32-only, for now.
<!--<syntaxhighlight lang="phix">(notonline)-->
 <span style="color: #000080;font-style:italic;">--
 -- demo\rosetta\Validate_XML.exw
 -- =============================
 --</span>
 <span style="color: #008080;">without</span> <span style="color: #008080;">js</span>
 <span style="color: #7060A8;">requires</span><span style="color: #0000FF;">(</span><span style="color: #000000;">32</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">-- let me know if you can get this to work on 64bit</span>
 <span style="color: #7060A8;">requires</span><span style="color: #0000FF;">(</span><span style="color: #004600;">WINDOWS</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">--   ""   if you can get this to work on linux</span>
 <span style="color: #008080;">constant</span> <span style="color: #000000;">dl</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">`Download rosetta\libxml\ from http://phix.x10.mx/pmwiki/pmwiki.php?n=Main.libxml`</span>
 <span style="color: #7060A8;">assert</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">get_file_type</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"libxml"</span><span style="color: #0000FF;">)=</span><span style="color: #004600;">FILETYPE_DIRECTORY</span><span style="color: #0000FF;">,</span><span style="color: #000000;">dl</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">include</span> <span style="color: #000000;">libxml</span><span style="color: #0000FF;">\</span><span style="color: #000000;">libxml</span><span style="color: #0000FF;">.</span><span style="color: #000000;">e</span>
 
 <span style="color: #008080;">constant</span> <span style="color: #000000;">XSDFileName</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">`libxml\shiporder.xsd`</span><span style="color: #0000FF;">,</span> <span style="color: #000080;font-style:italic;">-- (versions 2 & 3 also included in "")</span>
          <span style="color: #000000;">XMLFileName</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">`libxml\shiporder.xml`</span>
 
 <span style="color: #000000;">xmlLineNumbersDefault</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
 <span style="color: #004080;">atom</span> <span style="color: #000000;">pctxt</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">xmlSchemaNewParserCtxt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">XSDFileName</span><span style="color: #0000FF;">),</span>
      <span style="color: #000000;">schema</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">xmlSchemaParse</span><span style="color: #0000FF;">(</span><span style="color: #000000;">pctxt</span><span style="color: #0000FF;">)</span>
 <span style="color: #000000;">xmlSchemaFreeParserCtxt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">pctxt</span><span style="color: #0000FF;">)</span>
 <span style="color: #004080;">atom</span> <span style="color: #000000;">doc</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">xmlReadFile</span><span style="color: #0000FF;">(</span><span style="color: #000000;">XMLFileName</span><span style="color: #0000FF;">,</span> <span style="color: #004600;">NULL</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">0</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">if</span> <span style="color: #000000;">doc</span><span style="color: #0000FF;">=</span><span style="color: #004600;">NULL</span> <span style="color: #008080;">then</span>
     <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">2</span><span style="color: #0000FF;">,</span> <span style="color: #008000;">"Could not parse %s\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">XMLFileName</span><span style="color: #0000FF;">})</span>
 <span style="color: #008080;">else</span>
     <span style="color: #004080;">atom</span> <span style="color: #000000;">vctxt</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">xmlSchemaNewValidCtxt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">schema</span><span style="color: #0000FF;">)</span>
     <span style="color: #004080;">integer</span> <span style="color: #000000;">ret</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">xmlSchemaValidateDoc</span><span style="color: #0000FF;">(</span><span style="color: #000000;">vctxt</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">doc</span><span style="color: #0000FF;">)</span>
     <span style="color: #008080;">if</span> <span style="color: #000000;">ret</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
         <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"%s validates\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">XMLFileName</span><span style="color: #0000FF;">})</span>
     <span style="color: #008080;">elsif</span> <span style="color: #000000;">ret</span><span style="color: #0000FF;">></span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
         <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"%s fails to validate\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">XMLFileName</span><span style="color: #0000FF;">})</span>
     <span style="color: #008080;">else</span>
         <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"%s validation generated an internal error\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">XMLFileName</span><span style="color: #0000FF;">})</span>
     <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
     <span style="color: #000000;">xmlSchemaFreeValidCtxt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">vctxt</span><span style="color: #0000FF;">)</span>
     <span style="color: #000000;">xmlFreeDoc</span><span style="color: #0000FF;">(</span><span style="color: #000000;">doc</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
 <span style="color: #008080;">if</span> <span style="color: #000000;">schema</span><span style="color: #0000FF;">!=</span><span style="color: #004600;">NULL</span> <span style="color: #008080;">then</span>
     <span style="color: #000000;">xmlSchemaFree</span><span style="color: #0000FF;">(</span><span style="color: #000000;">schema</span><span style="color: #0000FF;">)</span>
 <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
 <span style="color: #000000;">xmlSchemaCleanupTypes</span><span style="color: #0000FF;">()</span>
 <span style="color: #000000;">xmlCleanupParser</span><span style="color: #0000FF;">()</span>
 <span style="color: #000000;">xmlMemoryDump</span><span style="color: #0000FF;">()</span>
<!--</syntaxhighlight>-->
{{out}}
<pre>
libxml\shiporder.xml validates
</pre>
Performing the same error handling check as Nim, ie changing orderperson to orderperson1 (twice) results in:
<pre>
Error/Warning in line 6
Element 'orderperson1': This element is not expected. Expected is ( orderperson ).
libxml\shiporder.xml fails to validate
</pre>
All three formats of the xsd file as given on the W3 page give identical results, for both with and without that error.

=={{header|PHP}}==
<syntaxhighlight lang="php">
libxml_use_internal_errors(true);

$xml = new DOMDocument();
$xml->load('shiporder.xml');

if (!$xml->schemaValidate('shiporder.xsd')) {
    var_dump(libxml_get_errors()); exit;
} else {
    echo 'success';
}
</syntaxhighlight>
{{out}}
<pre>
using valid shiporder.xml and shiporder.xsd:
success
Done.
using invalid shiporder.xml and valid shiporder.xsd:
array(1) {
  [0] =>
  class LibXMLError#2 (6) {
    public $level =>
    int(2)
    public $code =>
    int(1871)
    public $column =>
    int(0)
    public $message =>
    string(74) "Element 'foo': This element is not expected. Expected is ( orderperson ).
"
    public $file =>
    string(43) "file:/C:/xampp/htdocs/rosetta/shiporder.xml"
    public $line =>
    int(4)
  }
}
Done.
</pre>

=={{header|Python}}==

<syntaxhighlight lang="python">#!/bin/python
from __future__ import print_function
import lxml
from lxml import etree

if __name__=="__main__":

	parser = etree.XMLParser(dtd_validation=True)
	schema_root = etree.XML('''\
		<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
			<xsd:element name="a" type="xsd:integer"/>
		</xsd:schema>
		''')
	schema = etree.XMLSchema(schema_root)

	#Good xml
	parser = etree.XMLParser(schema = schema)
	try:
		root = etree.fromstring("<a>5</a>", parser)
		print ("Finished validating good xml")
	except lxml.etree.XMLSyntaxError as err:
		print (err)

	#Bad xml
	parser = etree.XMLParser(schema = schema)
	try:
		root = etree.fromstring("<a>5<b>foobar</b></a>", parser)
	except lxml.etree.XMLSyntaxError as err:
		print (err)</syntaxhighlight>

{{out}}
<pre>Finished validating good xml
Element 'a': Element content is not allowed, because the type definition is simple.</pre>

=={{header|Raku}}==
(formerly Perl 6)
{{trans|Perl}}
<syntaxhighlight lang="raku" line>
# Reference: https://github.com/libxml-raku/LibXML-raku

use v6.d;
use LibXML;
use LibXML::Schema;

my $good_xml         = '<a>5</a>';
my $bad_xml          = '<a>5<b>foobar</b></a>';

my $xsdschema = q:to<EOF>;
   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
      <xsd:element name="a" type="xsd:integer"/>
   </xsd:schema>
EOF

my LibXML $p .= new();

for ( $good_xml, $bad_xml ) {
   my $x = $p.parse: :string($_);
   try { LibXML::Schema.new( string => $xsdschema ).validate( $x ) }
   !$! ?? say "Valid." !! say $!.message() ;
}</syntaxhighlight>
{{out}}
<pre>Valid.
Schemas validity error : Element 'a': Element content is not allowed, because the type definition is simple.
</pre>

=={{header|Scala}}==
  <syntaxhighlight lang="scala">import java.net.URL

import javax.xml.XMLConstants.W3C_XML_SCHEMA_NS_URI
import javax.xml.transform.stream.StreamSource
import javax.xml.validation.SchemaFactory
import javax.xml.ws.Holder
import org.xml.sax.{ErrorHandler, SAXException, SAXParseException}

object XmlValidation extends App {
  val (schemaLocation, documentLocation) = (new URL("http://venus.eas.asu.edu/WSRepository/xml/Courses.xsd")
    , new URL("http://venus.eas.asu.edu/WSRepository/xml/Courses.xml"))

  println(s"Document is ${if (validate(schemaLocation, documentLocation)) "valid" else "invalid"}.")

  // A more complete validator
  def validate(schemaLocation: URL, documentLocation: URL): Boolean = {
    val factory = SchemaFactory.newInstance(W3C_XML_SCHEMA_NS_URI)
    val valid = new Holder[Boolean](true)
    try {
      val validator = factory.newSchema(schemaLocation).newValidator
      // Get some better diagnostics out
      validator.setErrorHandler(new ErrorHandler() {
        override def warning(exception: SAXParseException) = println("warning: " + exception.getMessage)

        override def error(exception: SAXParseException) = {
          println("error: " + exception.getMessage)
          valid.value = false
        }

        override def fatalError(exception: SAXParseException) = {
          println("fatal error: " + exception.getMessage)
          throw exception
        }
      })
      validator.validate(new StreamSource(documentLocation.toString))
      valid.value
    } catch {
      case _: SAXException =>
        // Already reported above
        false
      case e: Exception =>
        // If this is the only thing that throws, it's a gross error
        println(e)
        false
    }
  }
}</syntaxhighlight>

=={{header|Sidef}}==
{{trans|Perl}}
<syntaxhighlight lang="ruby">require('XML::LibXML')

func is_valid_xml(str, schema) {

    var parser    = %O<XML::LibXML>.new
    var xmlschema = %O<XML::LibXML::Schema>.new(string => schema)

    try {
        xmlschema.validate(parser.parse_string(str))
        true
    } catch {
        false
    }
}

var good_xml = '<a>5</a>'
var bad_xml  = '<a>5<b>foobar</b></a>'

var xmlschema_markup = <<'END'
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="a" type="xsd:integer"/>
</xsd:schema>
END

[good_xml, bad_xml].each { |xml|
    say "is_valid_xml(#{xml.dump}) : #{is_valid_xml(xml, xmlschema_markup)}"
}</syntaxhighlight>
{{out}}
<pre>
is_valid_xml("<a>5</a>") : true
is_valid_xml("<a>5<b>foobar</b></a>") : false
</pre>

=={{header|VBScript}}==
<syntaxhighlight lang="vb">
Option explicit

Function fileexists(fn) 
  fileexists= CreateObject("Scripting.FileSystemObject").FileExists(fn)
End Function

Function xmlvalid(strfilename)
  Dim xmldoc,xmldoc2,objSchemas 
  Set xmlDoc = CreateObject("Msxml2.DOMDocument.6.0")
  
  If fileexists(Replace(strfilename,".xml",".dtd")) Then
    xmlDoc.setProperty "ProhibitDTD", False
    xmlDoc.setProperty "ResolveExternals", True 
    xmlDoc.validateOnParse = True
    xmlDoc.async = False
    xmlDoc.load(strFileName)
  ElseIf fileexists(Replace(strfilename,".xml",".xsd")) Then
    xmlDoc.setProperty "ProhibitDTD", True
    xmlDoc.setProperty "ResolveExternals", True 
    xmlDoc.validateOnParse = True
    xmlDoc.async = False
    xmlDoc.load(strFileName)
    
    'import xsd
    Set xmlDoc2 = CreateObject("Msxml2.DOMDocument.6.0")
    xmlDoc2.validateOnParse = True
    xmlDoc2.async = False
    xmlDoc2.load(Replace (strfilename,".xml",".xsd"))
    
    'cache xsd
    Set objSchemas = CreateObject("MSXML2.XMLSchemaCache.6.0")
    objSchemas.Add "", xmlDoc2
  Else 
    Set xmlvalid= Nothing:Exit Function
  End If
  
  Set xmlvalid=xmldoc.parseError 
End Function



Sub displayerror (parserr) 'display the info returned by Msxml2
  Dim strresult
  If parserr is Nothing Then 
    strresult= "could not find dtd or xsd for " & strFileName
  Else   
    With parserr
     Select Case .errorcode
      Case 0 
        strResult = "Valid: " & strFileName & vbCr
      Case Else
        strResult = vbCrLf & "ERROR! Failed to validate " & _
        strFileName & vbCrLf &.reason & vbCr & _
        "Error code: " & .errorCode & ", Line: " & _
        .line & ", Character: " & _
        .linepos & ", Source: """ & _
        .srcText &  """ - " & vbCrLf 
 
      End Select
    End With
  End If
  WScript.Echo strresult
End Sub

'main
Dim strfilename

'testing validation with dtd
'strfilename="books.xml"
'displayerror xmlvalid (strfilename)

'testing validation with xsd
strfilename="shiporder.xml"
displayerror xmlvalid (strfilename)
</syntaxhighlight>
{{out}}
<small>
<pre>
Valid: shiporder.xml
</pre>
</small>

=={{header|Visual Basic .NET}}==
'''Compiler:''' Roslyn Visual Basic (language version >= 14, e.g. with Visual Studio 2015)
{{works with|.NET Core|2.1}}

<syntaxhighlight lang="vbnet">Option Compare Binary
Option Explicit On
Option Infer On
Option Strict On

Imports System.Xml
Imports System.Xml.Schema

Module Program
    Function GetValidationErrors(doc As XDocument, schemaSet As XmlSchemaSet) As IList(Of ValidationEventArgs)
        GetValidationErrors = New List(Of ValidationEventArgs)
        doc.Validate(schemaSet, Sub(sender, e) GetValidationErrors.Add(e))
    End Function

    Sub Main()
        ' These functions are declared in another module found below.
        Dim schema = GetSchema()
        Dim document = GetDocument()

        Dim schemaSet As New XmlSchemaSet()
        schemaSet.Add(XmlSchema.Read(schema.CreateReader(), Nothing))

        Dim errors = GetValidationErrors(document, schemaSet)
        For Each e In errors
            Console.WriteLine($"Validation {e.Severity}:{vbCrLf}{e.Message}")
        Next

        If errors.Count = 0 Then Console.WriteLine("The document is valid.")
    End Sub
End Module</syntaxhighlight>

{{out}}
<pre>Validation Error:
The 'an-attribute' attribute is invalid - The value 'wrong' is invalid according to its datatype 'http://www.w3.org/2001/XMLSchema:boolean' - The string 'wrong' is not a valid Boolean value.</pre>

An alternative is to use XmlReader (like the C# and F# examples [as of 2019-08-06]).

<syntaxhighlight lang="vbnet">    Function GetValidationErrorsXmlReader(doc As XDocument, schemaSet As XmlSchemaSet, warnings As Boolean) As IList(Of ValidationEventArgs)
        GetValidationErrorsReader = New List(Of ValidationEventArgs)

        Dim settings As New XmlReaderSettings()
        With settings
            .ValidationType = ValidationType.Schema
            .Schemas = schemaSet
            If warnings Then .ValidationFlags = .ValidationFlags Or XmlSchemaValidationFlags.ReportValidationWarnings
        End With

        AddHandler settings.ValidationEventHandler, Sub(sender, e) GetValidationErrorsReader.Add(e)

        Using reader = XmlReader.Create(doc.CreateReader(), settings)
            Do While reader.Read() : Loop
        End Using
    End Function</syntaxhighlight>

Creating the documents (same as F#) from strings (does not handle syntax errors):

<syntaxhighlight lang="vbnet">Module Constants
    Const SCHEMA As String =
"<?xml version='1.0'?>
<xs:schema id='an-element' targetNamespace='example' xmlns:mstns='example' xmlns='example' xmlns:xs='http://www.w3.org/2001/XMLSchema' attributeFormDefault='unqualified' elementFormDefault='qualified'>
    <xs:element name='an-element'>
        <xs:complexType>
            <xs:sequence minOccurs='0' maxOccurs='unbounded'>
                <xs:element name='another-element' nillable='true'>
                    <xs:complexType>
                        <xs:simpleContent>
                            <xs:extension base='xs:string'>
                                <xs:attribute name='an-attribute' form='unqualified' type='xs:boolean'/>
                            </xs:extension>
                        </xs:simpleContent>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>"

    Const DOCUMENT As String =
"<?xml version='1.0'?>
<an-element xmlns='example'>
    <another-element an-attribute='false'>...</another-element>
    <another-element an-attribute='wrong'>123</another-element>
</an-element>"

    Function GetSchema() As XDocument
        Return XDocument.Parse(SCHEMA)
    End Function

    Function GetDocument() As XDocument
        Return XDocument.Parse(DOCUMENT)
    End Function
End Module</syntaxhighlight>

Alternatively, we can be cheeky and use VB's XML literals...

<syntaxhighlight lang="vbnet">Module Constants
    Function GetDocument() As XDocument
        Return _
        <?xml version="1.0"?>
        <an-element xmlns="example">
            <another-element an-attribute="false">...</another-element>
            <another-element an-attribute="wrong"> 123</another-element>
        </an-element>
    End Function

    Function GetSchema() As XDocument
        Return _
        <?xml version="1.0"?>
        <xs:schema id="an-element" targetNamespace="example" xmlns:mstns="example" xmlns="example" xmlns:xs="http://www.w3.org/2001/XMLSchema" attributeFormDefault="unqualified" elementFormDefault="qualified">
            <xs:element name="an-element">
                <xs:complexType>
                    <xs:sequence minOccurs="0" maxOccurs="unbounded">
                        <xs:element name="another-element" nillable="true">
                            <xs:complexType>
                                <xs:simpleContent>
                                    <xs:extension base="xs:string">
                                        <xs:attribute name="an-attribute" form="unqualified" type="xs:boolean"/>
                                    </xs:extension>
                                </xs:simpleContent>
                            </xs:complexType>
                        </xs:element>
                    </xs:sequence>
                </xs:complexType>
            </xs:element>
        </xs:schema>
    End Function
End Module</syntaxhighlight>

=={{header|Wren}}==
{{trans|Nim}}
{{libheader|libxml2}}
Although Wren has third party support for XML, it does not support validation against an XSD schema. We therefore use an 
embedded program so we can ask the C host to communicate with Libxml2 for us.
<syntaxhighlight lang="wren">/* XML_validation.wren */

class Args {
    foreign static xmlFilename

    foreign static xsdFilename
}

foreign class XmlSchemaPtr {
    construct new() {}
}

foreign class XmlSchemaParserCtxtPtr {
    construct new(url) {}

    foreign parse(schema)

    foreign freeParserCtxt()
}

foreign class XmlSchemaValidCtxtPtr {
    construct new(schema) {}

    foreign validateFile(filename, options)

    foreign freeValidCtxt()
}

var xmlFilename = Args.xmlFilename
var xsdFilename = Args.xsdFilename

// parse xml schema file
var parserCtxt = XmlSchemaParserCtxtPtr.new(xsdFilename)
var schema = XmlSchemaPtr.new()
parserCtxt.parse(schema)
parserCtxt.freeParserCtxt()

// validate xml file using schema
var validCtxt = XmlSchemaValidCtxtPtr.new(schema)
var res = validCtxt.validateFile(xmlFilename, 0)
if (res == 0) {
    System.print("'%(xmlFilename)' validates.")
} else if (res == -1) {
    System.print("'%(xmlFilename)' validation generated an internal error.")
} else {
    System.print("'%(xmlFilename)' fails to validate.")
}
validCtxt.freeValidCtxt()</syntaxhighlight>
<br>
We now embed this in the following C program, compile and run it.
<syntaxhighlight lang="c">/* built with: gcc XML_validation.c -o XML_validation -I/usr/include/libxml2 -lxml2 -lwren -lm  */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libxml2/libxml/xmlschemastypes.h>
#include "wren.h"

/* C <=> Wren interface functions */

char *xmlFilename, *xsdFilename;

void C_xmlFilename(WrenVM* vm) {
    wrenSetSlotString(vm, 0, xmlFilename);
}

void C_xsdFilename(WrenVM* vm) {
    wrenSetSlotString(vm, 0, xsdFilename);
}

void C_xmlSchemaPtrAllocate(WrenVM* vm) {
    wrenSetSlotNewForeign(vm, 0, 0, sizeof(xmlSchemaPtr));
}

void C_xmlSchemaParserCtxtPtrAllocate(WrenVM* vm) {
    xmlSchemaParserCtxtPtr* pctxt = (xmlSchemaParserCtxtPtr*)wrenSetSlotNewForeign(vm, 0, 0, sizeof(xmlSchemaParserCtxtPtr));
    const char *url = wrenGetSlotString(vm, 1);
    *pctxt = xmlSchemaNewParserCtxt(url);
}

void C_xmlSchemaValidCtxtPtrAllocate(WrenVM* vm) {
    xmlSchemaValidCtxtPtr* pctxt = (xmlSchemaValidCtxtPtr*)wrenSetSlotNewForeign(vm, 0, 0, sizeof(xmlSchemaValidCtxtPtr));
    xmlSchemaPtr schema = *(xmlSchemaPtr*)wrenGetSlotForeign(vm, 1);
    *pctxt = xmlSchemaNewValidCtxt(schema);
}

void C_parse(WrenVM* vm) {
    xmlSchemaParserCtxtPtr ctxt = *(xmlSchemaParserCtxtPtr*)wrenGetSlotForeign(vm, 0);
    xmlSchemaPtr* pschema = (xmlSchemaPtr*)wrenGetSlotForeign(vm, 1);
    *pschema = xmlSchemaParse(ctxt);
}

void C_freeParserCtxt(WrenVM* vm) {
    xmlSchemaParserCtxtPtr ctxt = *(xmlSchemaParserCtxtPtr*)wrenGetSlotForeign(vm, 0);
    xmlSchemaFreeParserCtxt(ctxt);
}

void C_validateFile(WrenVM* vm) {
    xmlSchemaValidCtxtPtr ctxt = *(xmlSchemaValidCtxtPtr*)wrenGetSlotForeign(vm, 0);
    const char *filename = wrenGetSlotString(vm, 1);
    int options = (int)wrenGetSlotDouble(vm, 2);
    int res = xmlSchemaValidateFile(ctxt, filename, options);
    wrenSetSlotDouble(vm, 0, (double)res);
}

void C_freeValidCtxt(WrenVM* vm) {
    xmlSchemaValidCtxtPtr ctxt = *(xmlSchemaValidCtxtPtr*)wrenGetSlotForeign(vm, 0);
    xmlSchemaFreeValidCtxt(ctxt);
}

WrenForeignClassMethods bindForeignClass(WrenVM* vm, const char* module, const char* className) {
    WrenForeignClassMethods methods;
    methods.allocate = NULL;
    methods.finalize = NULL;
    if (strcmp(module, "main") == 0) {
        if (strcmp(className, "XmlSchemaPtr") == 0) {
            methods.allocate = C_xmlSchemaPtrAllocate;
        } else if (strcmp(className, "XmlSchemaParserCtxtPtr") == 0) {
            methods.allocate = C_xmlSchemaParserCtxtPtrAllocate;
        } else if (strcmp(className, "XmlSchemaValidCtxtPtr") == 0) {
            methods.allocate = C_xmlSchemaValidCtxtPtrAllocate;
        }
    }
    return methods;
}

WrenForeignMethodFn bindForeignMethod(
    WrenVM* vm,
    const char* module,
    const char* className,
    bool isStatic,
    const char* signature) {
    if (strcmp(module, "main") == 0) {
        if (strcmp(className, "Args") == 0) {
            if (isStatic && strcmp(signature, "xmlFilename") == 0) return C_xmlFilename;
            if (isStatic && strcmp(signature, "xsdFilename") == 0) return C_xsdFilename;
        } else if (strcmp(className, "XmlSchemaParserCtxtPtr") == 0) {
            if (!isStatic && strcmp(signature, "parse(_)") == 0) return C_parse;
            if (!isStatic && strcmp(signature, "freeParserCtxt()") == 0) return C_freeParserCtxt;
        } else if (strcmp(className, "XmlSchemaValidCtxtPtr") == 0) {
            if (!isStatic && strcmp(signature, "validateFile(_,_)") == 0) return C_validateFile;
            if (!isStatic && strcmp(signature, "freeValidCtxt()") == 0) return C_freeValidCtxt;
        }
    }
    return NULL;
}

static void writeFn(WrenVM* vm, const char* text) {
    printf("%s", text);
}

void errorFn(WrenVM* vm, WrenErrorType errorType, const char* module, const int line, const char* msg) {
    switch (errorType) {
        case WREN_ERROR_COMPILE:
            printf("[%s line %d] [Error] %s\n", module, line, msg);
            break;
        case WREN_ERROR_STACK_TRACE:
            printf("[%s line %d] in %s\n", module, line, msg);
            break;
        case WREN_ERROR_RUNTIME:
            printf("[Runtime Error] %s\n", msg);
            break;
    }
}

char *readFile(const char *fileName) {
    FILE *f = fopen(fileName, "r");
    fseek(f, 0, SEEK_END);
    long fsize = ftell(f);
    rewind(f);
    char *script = malloc(fsize + 1);
    fread(script, 1, fsize, f);
    fclose(f);
    script[fsize] = 0;
    return script;
}

int main(int argc, char **argv) {
    if (argc <= 2) {
		printf("Usage: %s <XML Document Name> <XSD Document Name>\n", argv[0]);
		return 0;
	}
    xmlFilename = argv[1];
    xsdFilename = argv[2];
    WrenConfiguration config;
    wrenInitConfiguration(&config);
    config.writeFn = &writeFn;
    config.errorFn = &errorFn;
    config.bindForeignClassFn = &bindForeignClass;
    config.bindForeignMethodFn = &bindForeignMethod;
    WrenVM* vm = wrenNewVM(&config);
    const char* module = "main";
    const char* fileName = "XML_validation.wren";
    char *script = readFile(fileName);
    WrenInterpretResult result = wrenInterpret(vm, module, script);
    switch (result) {
        case WREN_RESULT_COMPILE_ERROR:
            printf("Compile Error!\n");
            break;
        case WREN_RESULT_RUNTIME_ERROR:
            printf("Runtime Error!\n");
            break;
        case WREN_RESULT_SUCCESS:
            break;
    }
    wrenFreeVM(vm);
    free(script);
    return 0;
}</syntaxhighlight> 

{{out}}
Using command <code>./XML_validation shiporder.xml shiporder.xsd</code>:
<pre>'shiporder.xml' validates.</pre>
Using a modified file “shiporder1.xml” where tag “orderperson” has been replaced by “orderperson1”:
<pre>Entity: line 6: Schemas validity error : Element 'orderperson1': This element is not expected. Expected is ( orderperson ).
'shiporder1.xml' fails to validate.</pre>