TinyXML教程
這是什麼？
這個教程對如何有效地使用TinyXML有幾個技巧與建議。
我也會盡量包含一些C++的小技巧，如如何將string類型轉換爲整形和反過來轉換。這並不是只針對TinyXML自身，只是因爲它或許對你的項目有用，所以我才放在本文的一些地方。
如果你並不瞭解基本的C++概念，這篇教程對你並沒有用。同樣地，如果你不知道DOM是什麼，先到別的地方瞭解一下。
在開始之前
一些將要被用到的XML數據組或文件。
example1.xml:
<?xmlversion="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>
開始
從文件中載入XML
從文件導入到TinyXML DOM的最簡單方法就是：
TiXmlDocument doc( "demo.xml" );
doc.LoadFile();
下面展示了一個更實用的方法。它會載入文件並且將文件內容顯示到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);
}
}
最簡單的證實這個函數的方法是使用像下面一樣的main函數：
int main(void)
{
dump_to_stdout("example1.xml");
return 0;
}
回顧Example 1中的XML：
<?xml version="1.0" ?>
<Hello>World</Hello>
使用這個XML運行上面的程序將在控制檯/DOS窗口中輸出如下的結果：
DOCUMENT
+ DECLARATION
+ ELEMENT Hello
+ TEXT[World]
“dump_to_stdout”函數會在本教程的下面重新定義，如果你想理解遞歸遍歷一個DOM，這將非常有用。
程序化創建文檔
這是如何程序化構建Example 1：
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" );
}
這個文件可以通過如下方法載入並且顯示在控制檯：
dump_to_stdout("madeByHand.xml"); // 這個函數將會在本教程後續定義
你會發現它與Example 1相同：
madeByHand.xml:
Document
+ Declaration
+ Element [Hello]
+ Text: [World]
這個代碼生成完全相同的XML DOM，但是它卻展示了創建與連接節點的不同順序：
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" );
}
這些都產生相同的XML：
<?xml version="1.0" ?>
<Hello>World</Hello>
或者相同的結構：
DOCUMENT
+ DECLARATION
+ ELEMENT Hello
+ TEXT[World]
屬性（Attributes）
給一個存在的節點設置屬性是簡單的：
window = new TiXmlElement( "Demo" );
window->SetAttribute("name", "Circle");
window->SetAttribute("x", 5);
window->SetAttribute("y", 15);
window->SetDoubleAttribute("radius", 3.14159);
只要你想，你就可以讓它通過TiXmlAttribute類實現。
下面的代碼展示了一個（並不是唯一）獲取節點所有屬性的方法，打印名稱和字符值，並且如果這些值能夠轉換爲整型或double類型，打印這些值：
// 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;
}
將文檔寫入文件
將一個預先構建的DOM寫入文件是個簡單的事：
doc.SaveFile( saveFilename );
回憶，例如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>
如下的函數創建了這個DOM並且寫入”appsettings.xml“文件：
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" );
}
函數dump_to_stdout將顯示這個結構：
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
我對TinyXML默認地按照別的APIs所謂的”整潔“方式寫XML文檔感到奇怪。它改變了包含別的節點的元素文本的空白字符，因此它寫成了包含層次嵌套的樹狀。
我並沒有看到有方法去關閉寫文件時的縮進，使界限相對簡單。
[Lee:這在STL模式時很簡單，僅僅只需使用cout<< myDoc。非STL模式總是以“整潔”模式顯示。添加一個開關是一個非常好的功能並且正在考慮中。]
XML到C++對象/C++對象到XML
介紹
這個例子結舌你已經學過了從XML文件中導入程序設置與將程序配置寫入XML文件，如類似example4.xml。
有許多實現的方法。例如，研究TinyBind項目（http://sourceforge.net/projects/tinybind）。
這個章節介紹一個使用XML讀入與寫出基本對象結構的悠久方法。
設置你的類對象
以幾個基本類開始，就像：
#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;
}
};
這是一個基本的main函數，它展示瞭如何創建一個節本的對象樹，並隨後保存和載入：
int main(void)
{
AppSettings settings;
settings.save("appsettings2.xml");
settings.load("appsettings2.xml");
return 0;
}
下面的main函數展示創建、修改、保存和載入一個預設的結構：
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;
}
當save()與load()結束時（看下面），運行main()在控制檯上顯示：
HitchHikerApp: Don't Panic
HitchHikerApp: Show window 'BookFrame' at 15,25 (300 x 100)
HitchHikerApp: Thanks for all the fish
C++ XML編碼
實現保存到一個文件有很多種方法。這就是其中之一：
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);
}
修改main函數並且運行它會產生如下的文件：
<?xml version="1.0" ?>
<HitchHikerApp>
<!-- Settings for HitchHikerApp -->
<Messages>
<Farewell>Thanks for all the fish</Farewell>
<Welcome>Don'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>
XML解碼
與對象編碼類似，有很多方法將XML解碼成C++對象結構。下面的方法使用了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);
}
}
}
完整的dump_to_stdout
下面是一個可以複製與粘貼的程序例子，它可以載入XML屬性和通過前面提到的遞歸遍歷方式將這種結構展示到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::TINYXML_DOCUMENT:
printf( "Document" );
break;
case TiXmlNode::TINYXML_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::TINYXML_COMMENT:
printf( "Comment: [%s]", pParent->Value());
break;
case TiXmlNode::TINYXML_UNKNOWN:
printf( "Unknown" );
break;
case TiXmlNode::TINYXML_TEXT:
pText = pParent->ToText();
printf( "Text: [%s]", pText->Value() );
break;
case TiXmlNode::TINYXML_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;
}
在命令行或者DOS窗口中運行，如下：
C:\dev\tinyxml> Debug\tinyxml_1.exe example1.xml
example1.xml:
Document
+ Declaration
+ Element [Hello]
(No attributes)
+ Text: [World]
注：本文翻譯自TinyXML的源碼文檔，如果不恰當之處，請不吝賜教，謝謝！