Validate XML using Windows DOM and TXMLDocument: doesn't work on some computers

Question

I have some Delphi code to read and validates XML files based on an XSD document. I am using using Windows DOM (TMXLDocument). This Article explains the underlying logic.<

Answer 1

I know this question is tagged for Delphi, but I thought some Embarcadero C++ Builder users might benefit from seeing a C++ implementation of Remy's last example using MSXML2 OLE objects.

I know I wish someone would have posted this a few days ago. XD

.h file:

//------------------------------------------------------------------------------
#ifndef XmlValidatorUH
#define XmlValidatorUH
//------------------------------------------------------------------------------
class PACKAGE TXmlValidator
{
private:
    Variant FSchemaCache;
    Variant FXmlDomDoc;

    // TAutoCmd Variables
    Procedure   CacheProcAdd;
    PropertySet CacheSetValidateOnLoad;

    Procedure   XmlProcLoadXml;
    PropertySet XmlSetValidateOnParse;
    PropertySet XmlSetResolveExternals;
    PropertySet XmlSetSchemas;
    PropertyGet XmlGetParseError;

    PropertyGet ParseErrorGetReason;

public:
    __fastcall TXmlValidator( String _SchemaLocation );

    String __fastcall ValidationError( String _Xml );

};
//------------------------------------------------------------------------------

#endif

.cpp file:

//------------------------------------------------------------------------------
#include 
#pragma hdrstop
//------------------------------------------------------------------------------
#include "XmlValidatorU.h"
#include 
//------------------------------------------------------------------------------
#pragma package(smart_init)
//------------------------------------------------------------------------------
// Validates XML against Schema
//------------------------------------------------------------------------------
// This class uses OLE objects from MSXML2 to validate XML from an XSD file.
// Generally, use the following steps to deal with OLE objects:
//  1. Define a Variant variable for your OLE Object; assign using CreateOleObject().
//  2. Define your TAutoCmd objects that will be used in Variant.Exec()
//  3. Set TAutoCmd args using << to add settings
//  4. Once everything is set up, call Exec() on your OLE Object variant
// More documentation on OLE objects / TAutoCmd at:
//  http://docwiki.embarcadero.com/CodeExamples/Rio/en/AutoCmd_(C%2B%2B)
//------------------------------------------------------------------------------
// This macro clarifies that we're registering OLE Function names to our defined TAutoCmd variables.
//
#define RegisterAutoCmd( _AutoCmd, _OleFunc ) _AutoCmd( _OleFunc )
//------------------------------------------------------------------------------
// These macros clear AutoCmdArgs before setting them.
// I made these because setting an arg multiple times just stacks them up, changing the function signature.
// Then, OLE throws a "Member Not Found" error because it can't find a function with that signature.
//
#define AutoCmdArg( _AutoCmd, _Arg ) _AutoCmd.ClearArgs(); _AutoCmd << _Arg
#define AutoCmdArgs( _AutoCmd, _Arg1, _Arg2 ) AutoCmdArg( _AutoCmd, _Arg1 ); _AutoCmd << _Arg2
//------------------------------------------------------------------------------
__fastcall TXmlValidator::TXmlValidator( String _SchemaLocation )
    :
    RegisterAutoCmd( CacheProcAdd,              "add"               ),
    RegisterAutoCmd( CacheSetValidateOnLoad,    "validateOnLoad"    ),
    RegisterAutoCmd( XmlProcLoadXml,            "loadXML"           ),
    RegisterAutoCmd( XmlSetValidateOnParse,     "validateOnParse"   ),
    RegisterAutoCmd( XmlSetResolveExternals,    "resolveExternals"  ),
    RegisterAutoCmd( XmlSetSchemas,             "schemas"           ),
    RegisterAutoCmd( XmlGetParseError,          "parseError"        ),
    RegisterAutoCmd( ParseErrorGetReason,       "reason"            )
{
    if ( _SchemaLocation.IsEmpty() ) 
    { 
        throw Exception( String( __FUNC__ ) + " - Missing Schema Location" );
    }

    // Instantiate the OLE objects
    FSchemaCache    = CreateOleObject( "MSXML2.XMLSchemaCache.4.0"  );
    FXmlDomDoc      = CreateOleObject( "MSXML2.DOMDocument.4.0"     );

    // Set static args that shouldn't change
    AutoCmdArg( CacheSetValidateOnLoad, true );
    AutoCmdArg( XmlSetValidateOnParse,  true );
    AutoCmdArg( XmlSetResolveExternals, true );

    const AnsiString NoNameSpace = "";
    AutoCmdArgs( CacheProcAdd, NoNameSpace, AnsiString( _SchemaLocation ) );

    // Load Cache
    FSchemaCache.Exec( CacheSetValidateOnLoad   );  // Validate on Load
    FSchemaCache.Exec( CacheProcAdd             );  // Add Schema file location to the cache

    // Now that the cache is loaded, set cached schema as arg to XML
    AutoCmdArg( XmlSetSchemas, FSchemaCache );
}
//------------------------------------------------------------------------------
String __fastcall TXmlValidator::ValidationError( String _Xml )
{
    AutoCmdArg( XmlProcLoadXml, AnsiString( _Xml ) );

    FXmlDomDoc.Exec( XmlSetValidateOnParse  );
    FXmlDomDoc.Exec( XmlSetResolveExternals );
    FXmlDomDoc.Exec( XmlSetSchemas          );
    FXmlDomDoc.Exec( XmlProcLoadXml         );

    Variant ParseErr = FXmlDomDoc.Exec( XmlGetParseError );

    return ParseErr.Exec( ParseErrorGetReason );
}
//------------------------------------------------------------------------------