C++读写XML--TinyXML

C++语言解析XML文件使用最广泛的库是TinyXML，TinyXML对应的官方文档如下：

TinyXML官方文档：http://www.grinninglizard.com/tinyxmldocs/index.html

TinyXML官方教程：http://www.grinninglizard.com/tinyxmldocs/tutorial0.html

本文主要参考官方文档，梳理出几个常用的功能，详细描述参见官方文档，

1 从文件中加载XML文档

下面代码将加载一个文件并将内容展示到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);
	}
}

在main函数中的调用如下：

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

example1.xml的内容如下：

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

执行上面程序运行结果如下：

DOCUMENT
+ DECLARATION
+ ELEMENT Hello
  + TEXT[World]

备注：函数``dump_to_stdout`` 的定义文章最后。

2 构建一个XML文档

需要构建的appsettings.xml内容如下：

<?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>

下面的函数将会构建这个DOM并写入到 “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" );  
} 

附录

Full listing for dump_to_stdout

// 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;
}