TinyXml: TinyXML Tutorial

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# TinyXML Tutorial

# What is this?

This tutorial has a few tips and suggestions on how to use TinyXML effectively.

I've also tried to include some C++ tips like how to convert strings to integers and vice versa. This isn't anything to do with TinyXML itself, but it may helpful for your project so I've put it in anyway.

If you don't know basic C++ concepts this tutorial won't be useful. Likewise if you don't know what a DOM is, look elsewhere first.

# Before we start

Some example XML datasets/files will be used.

example1.xml:

    <?xml version="1.0" ?>
    <Hello>World</Hello>

example2.xml:

    <?xml version="1.0" ?>
    <poetry>
    	<verse>
    		Alas
    		  Great World
    			Alas (again)
    	</verse>
    </poetry>

example3.xml:

    <?xml version="1.0" ?>
    <shapes>
    	<circle name="int-based" x="20" y="30" r="50" />
    	<point name="float-based" x="3.5" y="52.1" />
    </shapes>

example4.xml

    <?xml version="1.0" ?>
    <MyApp>
        <!-- Settings for MyApp -->
        <Messages>
            <Welcome>Welcome to MyApp</Welcome>
            <Farewell>Thank you for using MyApp</Farewell>
        </Messages>
        <Windows>
            <Window name="MainFrame" x="5" y="15" w="400" h="250" />
        </Windows>
        <Connection ip="192.168.0.1" timeout="123.456000" />
    </MyApp>

# Getting Started

## Load XML from a file

The simplest way to load a file into a TinyXML DOM is:

    TiXmlDocument doc( "demo.xml" );
    doc.LoadFile();

A more real-world usage is shown below. This will load the file and display the contents to STDOUT:

    // load the named file and dump its structure to STDOUT
    void dump_to_stdout(const char* pFilename)
    {
    	TiXmlDocument doc(pFilename);
    	bool loadOkay = doc.LoadFile();
    	if (loadOkay)
    	{
    		printf("\n%s:\n", pFilename);
    		dump_to_stdout( &doc ); // defined later in the tutorial
    	}
    	else
    	{
    		printf("Failed to load file \"%s\"\n", pFilename);
    	}
    }

A simple demonstration of this function is to use a main like this:

    int main(void)
    {
    	dump_to_stdout("example1.xml");
    	return 0;
    }

Recall that Example 1 XML is:

    <?xml version="1.0" ?>
    <Hello>World</Hello>

Running the program with this XML will display this in the console/DOS window:

    DOCUMENT
    + DECLARATION
    + ELEMENT Hello
      + TEXT[World]

The ``dump_to_stdout`` function is defined later in this tutorial and is useful if you want to understand recursive traversal of a DOM.

## Building Documents Programatically

This is how to build Example 1 pragmatically:

    void build_simple_doc( )
    {
    	// Make xml: <?xml ..><Hello>World</Hello>
    	TiXmlDocument doc;
    	TiXmlDeclaration * decl = new TiXmlDeclaration( "1.0", "", "" );
    	TiXmlElement * element = new TiXmlElement( "Hello" );
    	TiXmlText * text = new TiXmlText( "World" );
    	element->LinkEndChild( text );
    	doc.LinkEndChild( decl );
    	doc.LinkEndChild( element );
    	doc.SaveFile( "madeByHand.xml" );
    }

This can be loaded and displayed on the console with:

    dump_to_stdout("madeByHand.xml"); // this func defined later in the tutorial

and you'll see it is identical to Example 1:

    madeByHand.xml:
    Document
    + Declaration
    + Element [Hello]
      + Text: [World]

This code produces exactly the same XML DOM but it shows a different ordering to node creation and linking:

    void write_simple_doc2( )
    {
    	// same as write_simple_doc1 but add each node
    	// as early as possible into the tree.

    	TiXmlDocument doc;
    	TiXmlDeclaration * decl = new TiXmlDeclaration( "1.0", "", "" );
    	doc.LinkEndChild( decl );

    	TiXmlElement * element = new TiXmlElement( "Hello" );
    	doc.LinkEndChild( element );

    	TiXmlText * text = new TiXmlText( "World" );
    	element->LinkEndChild( text );

    	doc.SaveFile( "madeByHand2.xml" );
    }

Both of these produce the same XML, namely:

    <?xml version="1.0" ?>
    <Hello>World</Hello>

Or in structure form:

    DOCUMENT
    + DECLARATION
    + ELEMENT Hello
      + TEXT[World]

## Attributes

Given an existing node, settings attributes is easy:

    window = new TiXmlElement( "Demo" );
    window->SetAttribute("name", "Circle");
    window->SetAttribute("x", 5);
    window->SetAttribute("y", 15);
    window->SetDoubleAttribute("radius", 3.14159);

You can it also work with the TiXmlAttribute objects if you want.

The following code shows one way (not the only way) to get all attributes of an element, print the name and string value, and if the value can be converted to an integer or double, print that value too:

    // print all attributes of pElement.
    // returns the number of attributes printed
    int dump_attribs_to_stdout(TiXmlElement* pElement, unsigned int indent)
    {
    	if ( !pElement ) return 0;

    	TiXmlAttribute* pAttrib=pElement->FirstAttribute();
    	int i=0;
    	int ival;
    	double dval;
    	const char* pIndent=getIndent(indent);
    	printf("\n");
    	while (pAttrib)
    	{
    		printf( "%s%s: value=[%s]", pIndent, pAttrib->Name(), pAttrib->Value());

    		if (pAttrib->QueryIntValue(&ival)==TIXML_SUCCESS)    printf( " int=%d", ival);
    		if (pAttrib->QueryDoubleValue(&dval)==TIXML_SUCCESS) printf( " d=%1.1f", dval);
    		printf( "\n" );
    		i++;
    		pAttrib=pAttrib->Next();
    	}
    	return i;
    }

## Writing a document to a file

Writing a pre-built DOM to a file is trivial:

    doc.SaveFile( saveFilename );

Recall, for example, example 4:

    <?xml version="1.0" ?>
    <MyApp>
        <!-- Settings for MyApp -->
        <Messages>
            <Welcome>Welcome to MyApp</Welcome>
            <Farewell>Thank you for using MyApp</Farewell>
        </Messages>
        <Windows>
            <Window name="MainFrame" x="5" y="15" w="400" h="250" />
        </Windows>
        <Connection ip="192.168.0.1" timeout="123.456000" />
    </MyApp>

The following function builds this DOM and writes the file "appsettings.xml":

    void write_app_settings_doc( )
    {
    	TiXmlDocument doc;
    	TiXmlElement* msg;
     	TiXmlDeclaration* decl = new TiXmlDeclaration( "1.0", "", "" );
    	doc.LinkEndChild( decl );

    	TiXmlElement * root = new TiXmlElement( "MyApp" );
    	doc.LinkEndChild( root );

    	TiXmlComment * comment = new TiXmlComment();
    	comment->SetValue(" Settings for MyApp " );
    	root->LinkEndChild( comment );

    	TiXmlElement * msgs = new TiXmlElement( "Messages" );
    	root->LinkEndChild( msgs );

    	msg = new TiXmlElement( "Welcome" );
    	msg->LinkEndChild( new TiXmlText( "Welcome to MyApp" ));
    	msgs->LinkEndChild( msg );

    	msg = new TiXmlElement( "Farewell" );
    	msg->LinkEndChild( new TiXmlText( "Thank you for using MyApp" ));
    	msgs->LinkEndChild( msg );

    	TiXmlElement * windows = new TiXmlElement( "Windows" );
    	root->LinkEndChild( windows );

    	TiXmlElement * window;
    	window = new TiXmlElement( "Window" );
    	windows->LinkEndChild( window );
    	window->SetAttribute("name", "MainFrame");
    	window->SetAttribute("x", 5);
    	window->SetAttribute("y", 15);
    	window->SetAttribute("w", 400);
    	window->SetAttribute("h", 250);

    	TiXmlElement * cxn = new TiXmlElement( "Connection" );
    	root->LinkEndChild( cxn );
    	cxn->SetAttribute("ip", "192.168.0.1");
    	cxn->SetDoubleAttribute("timeout", 123.456); // floating point attrib

    	dump_to_stdout( &doc );
    	doc.SaveFile( "appsettings.xml" );
    }

The dump_to_stdout function will show this structure:

    Document
    + Declaration
    + Element [MyApp]
     (No attributes)
      + Comment: [ Settings for MyApp ]
      + Element [Messages]
     (No attributes)
        + Element [Welcome]
     (No attributes)
          + Text: [Welcome to MyApp]
        + Element [Farewell]
     (No attributes)
          + Text: [Thank you for using MyApp]
      + Element [Windows]
     (No attributes)
        + Element [Window]
          + name: value=[MainFrame]
          + x: value=[5] int=5 d=5.0
          + y: value=[15] int=15 d=15.0
          + w: value=[400] int=400 d=400.0
          + h: value=[250] int=250 d=250.0
          5 attributes
      + Element [Connection]
        + ip: value=[192.168.0.1] int=192 d=192.2
        + timeout: value=[123.456000] int=123 d=123.5
        2 attributes

I was surprised that TinyXml, by default, writes the XML in what other APIs call a "pretty" format - it modifies the whitespace of text of elements that contain other nodes so that writing the tree includes an indication of nesting level.

I haven't looked yet to see if there is a way to turn off indenting when writing a file - its bound to be easy.

[Lee: It's easy in STL mode, just use cout << myDoc. Non-STL mode is always in "pretty" format. Adding a switch would be a nice feature and has been requested.]

# XML to/from C++ objects

## Intro

This example assumes you're loading and saving your app settings in an XML file, e.g. something like example4.xml.

There are a number of ways to do this. For example, look into the TinyBind project at http://sourceforge.net/projects/tinybind

This section shows a plain-old approach to loading and saving a basic object structure using XML.

## Set up your object classes

Start off with some basic classes like these:

    #include <string>
    #include <map>
    using namespace std;

    typedef std::map<std::string,std::string> MessageMap;

    // a basic window abstraction - demo purposes only
    class WindowSettings
    {
    public:
    	int x,y,w,h;
    	string name;

    	WindowSettings()
    		: x(0), y(0), w(100), h(100), name("Untitled")
    	{
    	}

    	WindowSettings(int x, int y, int w, int h, const string& name)
    	{
    		this->x=x;
    		this->y=y;
    		this->w=w;
    		this->h=h;
    		this->name=name;
    	}
    };

    class ConnectionSettings
    {
    public:
    	string ip;
    	double timeout;
    };

    class AppSettings
    {
    public:
    	string m_name;
    	MessageMap m_messages;
    	list<WindowSettings> m_windows;
    	ConnectionSettings m_connection;

    	AppSettings() {}

    	void save(const char* pFilename);
    	void load(const char* pFilename);

    	// just to show how to do it
    	void setDemoValues()
    	{
    		m_name="MyApp";
    		m_messages.clear();
    		m_messages["Welcome"]="Welcome to "+m_name;
    		m_messages["Farewell"]="Thank you for using "+m_name;
    		m_windows.clear();
    		m_windows.push_back(WindowSettings(15,15,400,250,"Main"));
    		m_connection.ip="Unknown";
    		m_connection.timeout=123.456;
    	}
    };

This is a basic main() that shows how to create a default settings object tree, save it and load it again:

    int main(void)
    {
    	AppSettings settings;

    	settings.save("appsettings2.xml");
    	settings.load("appsettings2.xml");
    	return 0;
    }

The following main() shows creation, modification, saving and then loading of a settings structure:

    int main(void)
    {
    	// block: customise and save settings
    	{
    		AppSettings settings;
    		settings.m_name="HitchHikerApp";
    		settings.m_messages["Welcome"]="Don't Panic";
    		settings.m_messages["Farewell"]="Thanks for all the fish";
    		settings.m_windows.push_back(WindowSettings(15,25,300,250,"BookFrame"));
    		settings.m_connection.ip="192.168.0.77";
    		settings.m_connection.timeout=42.0;

    		settings.save("appsettings2.xml");
    	}

    	// block: load settings
    	{
    		AppSettings settings;
    		settings.load("appsettings2.xml");
    		printf("%s: %s\n", settings.m_name.c_str(),
    			settings.m_messages["Welcome"].c_str());
    		WindowSettings & w=settings.m_windows.front();
    		printf("%s: Show window '%s' at %d,%d (%d x %d)\n",
    			settings.m_name.c_str(), w.name.c_str(), w.x, w.y, w.w, w.h);
    		printf("%s: %s\n", settings.m_name.c_str(), settings.m_messages["Farewell"].c_str());
    	}
    	return 0;
    }

When the save() and load() are completed (see below), running this main() displays on the console:

    HitchHikerApp: Don't Panic
    HitchHikerApp: Show window 'BookFrame' at 15,25 (300 x 100)
    HitchHikerApp: Thanks for all the fish

## Encode C++ state as XML

There are lots of different ways to approach saving this to a file. Here's one:

    void AppSettings::save(const char* pFilename)
    {
    	TiXmlDocument doc;
    	TiXmlElement* msg;
    	TiXmlComment * comment;
    	string s;
     	TiXmlDeclaration* decl = new TiXmlDeclaration( "1.0", "", "" );
    	doc.LinkEndChild( decl );

    	TiXmlElement * root = new TiXmlElement(m_name.c_str());
    	doc.LinkEndChild( root );

    	comment = new TiXmlComment();
    	s=" Settings for "+m_name+" ";
    	comment->SetValue(s.c_str());
    	root->LinkEndChild( comment );

    	// block: messages
    	{
    		MessageMap::iterator iter;

    		TiXmlElement * msgs = new TiXmlElement( "Messages" );
    		root->LinkEndChild( msgs );

    		for (iter=m_messages.begin(); iter != m_messages.end(); iter++)
    		{
    			const string & key=(*iter).first;
    			const string & value=(*iter).second;
    			msg = new TiXmlElement(key.c_str());
    			msg->LinkEndChild( new TiXmlText(value.c_str()));
    			msgs->LinkEndChild( msg );
    		}
    	}

    	// block: windows
    	{
    		TiXmlElement * windowsNode = new TiXmlElement( "Windows" );
    		root->LinkEndChild( windowsNode );

    		list<WindowSettings>::iterator iter;

    		for (iter=m_windows.begin(); iter != m_windows.end(); iter++)
    		{
    			const WindowSettings& w=*iter;

    			TiXmlElement * window;
    			window = new TiXmlElement( "Window" );
    			windowsNode->LinkEndChild( window );
    			window->SetAttribute("name", w.name.c_str());
    			window->SetAttribute("x", w.x);
    			window->SetAttribute("y", w.y);
    			window->SetAttribute("w", w.w);
    			window->SetAttribute("h", w.h);
    		}
    	}

    	// block: connection
    	{
    		TiXmlElement * cxn = new TiXmlElement( "Connection" );
    		root->LinkEndChild( cxn );
    		cxn->SetAttribute("ip", m_connection.ip.c_str());
    		cxn->SetDoubleAttribute("timeout", m_connection.timeout);
    	}

    	doc.SaveFile(pFilename);
    }

Running this with the modified main produces this file:

    <?xml version="1.0" ?>
    <HitchHikerApp>
        <!-- Settings for HitchHikerApp -->
        <Messages>
            <Farewell>Thanks for all the fish</Farewell>
            <Welcome>Don&apos;t Panic</Welcome>
        </Messages>
        <Windows>
            <Window name="BookFrame" x="15" y="25" w="300" h="250" />
        </Windows>
        <Connection ip="192.168.0.77" timeout="42.000000" />
    </HitchHikerApp>

## Decoding state from XML

As with encoding objects, there are a number of approaches to decoding XML into your own C++ object structure. The following approach uses TiXmlHandles.

    void AppSettings::load(const char* pFilename)
    {
    	TiXmlDocument doc(pFilename);
    	if (!doc.LoadFile()) return;

    	TiXmlHandle hDoc(&doc);
    	TiXmlElement* pElem;
    	TiXmlHandle hRoot(0);

    	// block: name
    	{
    		pElem=hDoc.FirstChildElement().Element();
    		// should always have a valid root but handle gracefully if it does
    		if (!pElem) return;
    		m_name=pElem->Value();

    		// save this for later
    		hRoot=TiXmlHandle(pElem);
    	}

    	// block: string table
    	{
    		m_messages.clear(); // trash existing table

    		pElem=hRoot.FirstChild( "Messages" ).FirstChild().Element();
    		for( pElem; pElem; pElem=pElem->NextSiblingElement())
    		{
    			const char *pKey=pElem->Value();
    			const char *pText=pElem->GetText();
    			if (pKey && pText)
    			{
    				m_messages[pKey]=pText;
    			}
    		}
    	}

    	// block: windows
    	{
    		m_windows.clear(); // trash existing list

    		TiXmlElement* pWindowNode=hRoot.FirstChild( "Windows" ).FirstChild().Element();
    		for( pWindowNode; pWindowNode; pWindowNode=pWindowNode->NextSiblingElement())
    		{
    			WindowSettings w;
    			const char *pName=pWindowNode->Attribute("name");
    			if (pName) w.name=pName;

    			pWindowNode->QueryIntAttribute("x", &w.x); // If this fails, original value is left as-is
    			pWindowNode->QueryIntAttribute("y", &w.y);
    			pWindowNode->QueryIntAttribute("w", &w.w);
    			pWindowNode->QueryIntAttribute("hh", &w.h);

    			m_windows.push_back(w);
    		}
    	}

    	// block: connection
    	{
    		pElem=hRoot.FirstChild("Connection").Element();
    		if (pElem)
    		{
    			m_connection.ip=pElem->Attribute("ip");
    			pElem->QueryDoubleAttribute("timeout",&m_connection.timeout);
    		}
    	}
    }

# Full listing for dump_to_stdout

Below is a copy-and-paste demo program for loading arbitrary XML files and dumping the structure to STDOUT using the recursive traversal listed above.

    // tutorial demo program
    #include "stdafx.h"
    #include "tinyxml.h"

    // ----------------------------------------------------------------------
    // STDOUT dump and indenting utility functions
    // ----------------------------------------------------------------------
    const unsigned int NUM_INDENTS_PER_SPACE=2;

    const char * getIndent( unsigned int numIndents )
    {
    	static const char * pINDENT="                                      + ";
    	static const unsigned int LENGTH=strlen( pINDENT );
    	unsigned int n=numIndents*NUM_INDENTS_PER_SPACE;
    	if ( n > LENGTH ) n = LENGTH;

    	return &pINDENT[ LENGTH-n ];
    }

    // same as getIndent but no "+" at the end
    const char * getIndentAlt( unsigned int numIndents )
    {
    	static const char * pINDENT="                                        ";
    	static const unsigned int LENGTH=strlen( pINDENT );
    	unsigned int n=numIndents*NUM_INDENTS_PER_SPACE;
    	if ( n > LENGTH ) n = LENGTH;

    	return &pINDENT[ LENGTH-n ];
    }

    int dump_attribs_to_stdout(TiXmlElement* pElement, unsigned int indent)
    {
    	if ( !pElement ) return 0;

    	TiXmlAttribute* pAttrib=pElement->FirstAttribute();
    	int i=0;
    	int ival;
    	double dval;
    	const char* pIndent=getIndent(indent);
    	printf("\n");
    	while (pAttrib)
    	{
    		printf( "%s%s: value=[%s]", pIndent, pAttrib->Name(), pAttrib->Value());

    		if (pAttrib->QueryIntValue(&ival)==TIXML_SUCCESS)    printf( " int=%d", ival);
    		if (pAttrib->QueryDoubleValue(&dval)==TIXML_SUCCESS) printf( " d=%1.1f", dval);
    		printf( "\n" );
    		i++;
    		pAttrib=pAttrib->Next();
    	}
    	return i;
    }

    void dump_to_stdout( TiXmlNode* pParent, unsigned int indent = 0 )
    {
    	if ( !pParent ) return;

    	TiXmlNode* pChild;
    	TiXmlText* pText;
    	int t = pParent->Type();
    	printf( "%s", getIndent(indent));
    	int num;

    	switch ( t )
    	{
    	case TiXmlNode::DOCUMENT:
    		printf( "Document" );
    		break;

    	case TiXmlNode::ELEMENT:
    		printf( "Element [%s]", pParent->Value() );
    		num=dump_attribs_to_stdout(pParent->ToElement(), indent+1);
    		switch(num)
    		{
    			case 0:  printf( " (No attributes)"); break;
    			case 1:  printf( "%s1 attribute", getIndentAlt(indent)); break;
    			default: printf( "%s%d attributes", getIndentAlt(indent), num); break;
    		}
    		break;

    	case TiXmlNode::COMMENT:
    		printf( "Comment: [%s]", pParent->Value());
    		break;

    	case TiXmlNode::UNKNOWN:
    		printf( "Unknown" );
    		break;

    	case TiXmlNode::TEXT:
    		pText = pParent->ToText();
    		printf( "Text: [%s]", pText->Value() );
    		break;

    	case TiXmlNode::DECLARATION:
    		printf( "Declaration" );
    		break;
    	default:
    		break;
    	}
    	printf( "\n" );
    	for ( pChild = pParent->FirstChild(); pChild != 0; pChild = pChild->NextSibling())
    	{
    		dump_to_stdout( pChild, indent+1 );
    	}
    }

    // load the named file and dump its structure to STDOUT
    void dump_to_stdout(const char* pFilename)
    {
    	TiXmlDocument doc(pFilename);
    	bool loadOkay = doc.LoadFile();
    	if (loadOkay)
    	{
    		printf("\n%s:\n", pFilename);
    		dump_to_stdout( &doc ); // defined later in the tutorial
    	}
    	else
    	{
    		printf("Failed to load file \"%s\"\n", pFilename);
    	}
    }

    // ----------------------------------------------------------------------
    // main() for printing files named on the command line
    // ----------------------------------------------------------------------
    int main(int argc, char* argv[])
    {
    	for (int i=1; i<argc; i++)
    	{
    		dump_to_stdout(argv[i]);
    	}
    	return 0;
    }

Run this from the command line or a DOS window, e.g.:

    C:\dev\tinyxml> Debug\tinyxml_1.exe example1.xml

    example1.xml:
    Document
    + Declaration
    + Element [Hello]
     (No attributes)
      + Text: [World]

Authors and Changes

- Written by Ellers, April, May, June 2005
- Minor edits and integration into doc system, Lee Thomason September 2005
- Updated by Ellers, October 2005