XML实例

用户3519280

发布于 2023-07-06 14:58:41

1910

发布于 2023-07-06 14:58:41

文章被收录于专栏：c++ 学习分享

XML实例

TinyXML是一个非常小巧简单的XML解析库，采用DOM方式来解析XML文件。不足的是它本身不支持DTD和XSL，但普通简单的XML使用需求还是可以满足了。

TinyXML由2个头文件四个CPP文件构成。继承结构如下：

要操作XML首先需要加载XML，很简单：

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

一个更加真实的用例如下所示，加载一个XML文件然后显示内容到标准输出上。

// 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 
}  
else  
{  
    printf("Failed to load file \"%s\"\n", pFilename);  
}   
写个简单的Main函数
int main(void)  
{  
    dump_to_stdout("example1.xml");  
    return 0;  
} 
读下面的文件
<?xml version="1.0" ?>  
<Hello>World</Hello> 
输出如下
DECLARATION  
+ ELEMENT Hello  
  + TEXT[World]

dump_to_stdout递归遍历输出所有的XML内容，详细实现在本文的末尾。

TinyXML同样可以简单的编程生成一个上面的XML：

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" );  
}

与其等价的写法：

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" );  
}

给定一个节点，设置它的属性也很简单：

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

可以用下面的函数获得元素的所有属性：

// 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;  
}

我们经常通过配置文件来保存程序的一些配置信息。下面给一个实例来用XML加载和保存C++对象。

#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;  
    }  
};

类AppSettings提供了保存和加载配置信息的函数save和load。如下代码表示利用缺省的配置保存和加载：

int main(void)  
{  
    AppSettings settings;  
      
    settings.save("appsettings2.xml");  
    settings.load("appsettings2.xml");  
    return 0;  
}

同样的我们可以运行时修改配置：

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;  
}

有很多方法可以保存对象的属性信息，也就是对象的状态信息。下面的实例展示如何将对象的状态编码进XML文件。

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);    
}

下面的示例展示如何从XML文件中获得对象的状态信息

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);  
        }  
    }  
}  
函数dump_to_stdout如下：

#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);  
    }  
}

如果你想在MFC中使用TinyXML，会出现这样的编译错误 fatal error C1010: unexpected end of file while looking for precompiled header。因为预编译头文件通过编译stdafx.cpp生成，可以在4个实现CPP文件中引入头#include "stdafx.h"。记得放在最前面。这样就可以编译通过了。

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原始发表：2019-10-23，如有侵权请联系 cloudcommunity@tencent.com 删除

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