XML file: sample.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<root>
<ApplicationSettings
option_a = "10"
option_b = "24"
>
</ApplicationSettings>
<OtherStuff
option_x = "500"
>
</OtherStuff>
</root>Include file: parser.hpp
#ifndef XML_PARSER_HPP
#define XML_PARSER_HPP
/**
* @file
* Class "GetConfig" provides the functions to read the XML data.
* @version 1.0
*/
#include <xercesc/dom/DOM.hpp>
#include <xercesc/dom/DOMDocument.hpp>
#include <xercesc/dom/DOMDocumentType.hpp>
#include <xercesc/dom/DOMElement.hpp>
#include <xercesc/dom/DOMImplementation.hpp>
#include <xercesc/dom/DOMImplementationLS.hpp>
#include <xercesc/dom/DOMNodeIterator.hpp>
#include <xercesc/dom/DOMNodeList.hpp>
#include <xercesc/dom/DOMText.hpp>
#include <xercesc/parsers/XercesDOMParser.hpp>
#include <xercesc/util/XMLUni.hpp>
#include <string>
#include <stdexcept>
// Error codes
enum {
ERROR_ARGS = 1,
ERROR_XERCES_INIT,
ERROR_PARSE,
ERROR_EMPTY_DOCUMENT
};
class GetConfig
{
public:
GetConfig();
~GetConfig();
void readConfigFile(std::string&) throw(std::runtime_error);
char *getOptionA() { return m_OptionA; };
char *getOptionB() { return m_OptionB; };
private:
xercesc::XercesDOMParser *m_ConfigFileParser;
char* m_OptionA;
char* m_OptionB;
// Internal class use only. Hold Xerces data in UTF-16 SMLCh type.
XMLCh* TAG_root;
XMLCh* TAG_ApplicationSettings;
XMLCh* ATTR_OptionA;
XMLCh* ATTR_OptionB;
};
#endifC++ Program file: parser.cpp
#include <string>
#include <iostream>
#include <sstream>
#include <stdexcept>
#include <list>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include "parser.hpp"
using namespace xercesc;
using namespace std;
/**
* Constructor initializes xerces-C libraries.
* The XML tags and attributes which we seek are defined.
* The xerces-C DOM parser infrastructure is initialized.
*/
GetConfig::GetConfig()
{
try
{
XMLPlatformUtils::Initialize(); // Initialize Xerces infrastructure
}
catch( XMLException& e )
{
char* message = XMLString::transcode( e.getMessage() );
cerr << "XML toolkit initialization error: " << message << endl;
XMLString::release( &message );
// throw exception here to return ERROR_XERCES_INIT
}
// Tags and attributes used in XML file.
// Can't call transcode till after Xerces Initialize()
TAG_root = XMLString::transcode("root");
TAG_ApplicationSettings = XMLString::transcode("ApplicationSettings");
ATTR_OptionA = XMLString::transcode("option_a");
ATTR_OptionB = XMLString::transcode("option_b");
m_ConfigFileParser = new XercesDOMParser;
}
/**
* Class destructor frees memory used to hold the XML tag and
* attribute definitions. It als terminates use of the xerces-C
* framework.
*/
GetConfig::~GetConfig()
{
// Free memory
delete m_ConfigFileParser;
if(m_OptionA) XMLString::release( &m_OptionA );
if(m_OptionB) XMLString::release( &m_OptionB );
try
{
XMLString::release( &TAG_root );
XMLString::release( &TAG_ApplicationSettings );
XMLString::release( &ATTR_OptionA );
XMLString::release( &ATTR_OptionB );
}
catch( ... )
{
cerr << "Unknown exception encountered in TagNamesdtor" << endl;
}
// Terminate Xerces
try
{
XMLPlatformUtils::Terminate(); // Terminate after release of memory
}
catch( xercesc::XMLException& e )
{
char* message = xercesc::XMLString::transcode( e.getMessage() );
cerr << "XML ttolkit teardown error: " << message << endl;
XMLString::release( &message );
}
}
/**
* This function:
* - Tests the access and availability of the XML configuration file.
* - Configures the xerces-c DOM parser.
* - Reads and extracts the pertinent information from the XML config file.
*
* @param in configFile The text string name of the HLA configuration file.
*/
void GetConfig::readConfigFile(string& configFile)
throw( std::runtime_error )
{
// Test to see if the file is ok.
struct stat fileStatus;
int iretStat = stat(configFile.c_str(), &fileStatus);
if( iretStat == ENOENT )
throw ( std::runtime_error("Path file_name does not exist, or path is an empty string.") );
else if( iretStat == ENOTDIR )
throw ( std::runtime_error("A component of the path is not a directory."));
else if( iretStat == ELOOP )
throw ( std::runtime_error("Too many symbolic links encountered while traversing the path."));
else if( iretStat == EACCES )
throw ( std::runtime_error("Permission denied."));
else if( iretStat == ENAMETOOLONG )
throw ( std::runtime_error("File can not be read\n"));
// Configure DOM parser.
m_ConfigFileParser->setValidationScheme( XercesDOMParser::Val_Never );
m_ConfigFileParser->setDoNamespaces( false );
m_ConfigFileParser->setDoSchema( false );
m_ConfigFileParser->setLoadExternalDTD( false );
try
{
m_ConfigFileParser->parse( configFile.c_str() );
// no need to free this pointer - owned by the parent parser object
DOMDocument* xmlDoc = m_ConfigFileParser->getDocument();
// Get the top-level element: NAme is "root". No attributes for "root"
DOMElement* elementRoot = xmlDoc->getDocumentElement();
if( !elementRoot ) throw(std::runtime_error( "empty XML document" ));
// Parse XML file for tags of interest: "ApplicationSettings"
// Look one level nested within "root". (child of root)
DOMNodeList* children = elementRoot->getChildNodes();
const XMLSize_t nodeCount = children->getLength();
// For all nodes, children of "root" in the XML tree.
for( XMLSize_t xx = 0; xx < nodeCount; ++xx )
{
DOMNode* currentNode = children->item(xx);
if( currentNode->getNodeType() && // true is not NULL
currentNode->getNodeType() == DOMNode::ELEMENT_NODE ) // is element
{
// Found node which is an Element. Re-cast node as element
DOMElement* currentElement
= dynamic_cast< xercesc::DOMElement* >( currentNode );
if( XMLString::equals(currentElement->getTagName(), TAG_ApplicationSettings))
{
// Already tested node as type element and of name "ApplicationSettings".
// Read attributes of element "ApplicationSettings".
const XMLCh* xmlch_OptionA
= currentElement->getAttribute(ATTR_OptionA);
m_OptionA = XMLString::transcode(xmlch_OptionA);
const XMLCh* xmlch_OptionB
= currentElement->getAttribute(ATTR_OptionB);
m_OptionB = XMLString::transcode(xmlch_OptionB);
break; // Data found. No need to look at other elements in tree.
}
}
}
}
catch( xercesc::XMLException& e )
{
char* message = xercesc::XMLString::transcode( e.getMessage() );
ostringstream errBuf;
errBuf << "Error parsing file: " << message << flush;
XMLString::release( &message );
}
}
#ifdef MAIN_TEST
/* This main is provided for unit test of the class. */
int main()
{
string configFile="sample.xml"; // stat file. Get ambigious segfault otherwise.
GetConfig appConfig;
appConfig.readConfigFile(configFile);
cout << "Application option A=" << appConfig.getOptionA() << endl;
cout << "Application option B=" << appConfig.getOptionB() << endl;
return 0;
}
#endif