外國人寫的讀取config檔案
Config.h

    //Config.h  
    #pragma once  

    #include <string>  
    #include <map>  
    #include <iostream>  
    #include <fstream>  
    #include <sstream>  


    /* 
    * \brief Generic configuration Class 
    * 
    */  
    class Config {  
        // Data  
 

    protected:  
        std::string m_Delimiter;  //!< separator between key and value  
        std::string m_Comment;    //!< separator between value and comments  
        std::map<std::string,std::string> m_Contents;  //!< extracted keys and values  

        typedef std::map<std::string
 
,std::string>::iterator mapi;  
        typedef std::map<std::string,std::string>::const_iterator mapci;  
        // Methods  
    public:  

        Config( std::string filename,std::string delimiter = "=",std::string comment = "#" );  
        Config();  
        template<class T> T Read( const
 
 std::string& in_key ) const;  //!<Search for key and read value or optional default value, call as read<T>  
        template<class T> T Read( const std::string& in_key, const T& in_value ) const;  
        template<class T> bool ReadInto( T& out_var, const std::string& in_key ) const;  
        template<class T>  
        bool ReadInto( T& out_var, const std::string& in_key, const T& in_value ) const;  
        bool FileExist(std::string filename);  
        void ReadFile(std::string filename,std::string delimiter = "=",std::string comment = "#" );  

        // Check whether key exists in configuration  
        bool KeyExists( const std::string& in_key ) const;  

        // Modify keys and values  
        template<class T> void Add( const std::string& in_key, const T& in_value );  
        void Remove( const std::string& in_key );  

        // Check or change configuration syntax  
        std::string GetDelimiter() const { return m_Delimiter; }  
        std::string GetComment() const { return m_Comment; }  
        std::string SetDelimiter( const std::string& in_s )  
        { std::string old = m_Delimiter;  m_Delimiter = in_s;  return old; }    
        std::string SetComment( const std::string& in_s )  
        { std::string old = m_Comment;  m_Comment =  in_s;  return old; }  

        // Write or read configuration  
        friend std::ostream& operator<<( std::ostream& os, const Config& cf );  
        friend std::istream& operator>>( std::istream& is, Config& cf );  

    protected:  
        template<class T> static std::string T_as_string( const T& t );  
        template<class T> static T string_as_T( const std::string& s );  
        static void Trim( std::string& inout_s );  


        // Exception types  
    public:  
        struct File_not_found {  
            std::string filename;  
            File_not_found( const std::string& filename_ = std::string() )  
                : filename(filename_) {} };  
            struct Key_not_found {  // thrown only by T read(key) variant of read()  
                std::string key;  
                Key_not_found( const std::string& key_ = std::string() )  
                    : key(key_) {} };  
    };  


    /* static */  
    template<class T>  
    std::string Config::T_as_string( const T& t )  
    {  
        // Convert from a T to a string  
        // Type T must support << operator  
        std::ostringstream ost;  
        ost << t;  
        return ost.str();  
    }  


    /* static */  
    template<class T>  
    T Config::string_as_T( const std::string& s )  
    {  
        // Convert from a string to a T  
        // Type T must support >> operator  
        T t;  
        std::istringstream ist(s);  
        ist >> t;  
        return t;  
    }  


    /* static */  
    template<>  
    inline std::string Config::string_as_T<std::string>( const std::string& s )  
    {  
        // Convert from a string to a string  
        // In other words, do nothing  
        return s;  
    }  


    /* static */  
    template<>  
    inline bool Config::string_as_T<bool>( const std::string& s )  
    {  
        // Convert from a string to a bool  
        // Interpret "false", "F", "no", "n", "0" as false  
        // Interpret "true", "T", "yes", "y", "1", "-1", or anything else as true  
        bool b = true;  
        std::string sup = s;  
        for( std::string::iterator p = sup.begin(); p != sup.end(); ++p )  
            *p = toupper(*p);  // make string all caps  
        if( sup==std::string("FALSE") || sup==std::string("F") ||  
            sup==std::string("NO") || sup==std::string("N") ||  
            sup==std::string("0") || sup==std::string("NONE") )  
            b = false;  
        return b;  
    }  


    template<class T>  
    T Config::Read( const std::string& key ) const  
    {  
        // Read the value corresponding to key  
        mapci p = m_Contents.find(key);  
        if( p == m_Contents.end() ) throw Key_not_found(key);  
        return string_as_T<T>( p->second );  
    }  


    template<class T>  
    T Config::Read( const std::string& key, const T& value ) const  
    {  
        // Return the value corresponding to key or given default value  
        // if key is not found  
        mapci p = m_Contents.find(key);  
        if( p == m_Contents.end() ) return value;  
        return string_as_T<T>( p->second );  
    }  


    template<class T>  
    bool Config::ReadInto( T& var, const std::string& key ) const  
    {  
        // Get the value corresponding to key and store in var  
        // Return true if key is found  
        // Otherwise leave var untouched  
        mapci p = m_Contents.find(key);  
        bool found = ( p != m_Contents.end() );  
        if( found ) var = string_as_T<T>( p->second );  
        return found;  
    }  


    template<class T>  
    bool Config::ReadInto( T& var, const std::string& key, const T& value ) const  
    {  
        // Get the value corresponding to key and store in var  
        // Return true if key is found  
        // Otherwise set var to given default  
        mapci p = m_Contents.find(key);  
        bool found = ( p != m_Contents.end() );  
        if( found )  
            var = string_as_T<T>( p->second );  
        else  
            var = value;  
        return found;  
    }  


    template<class T>  
    void Config::Add( const std::string& in_key, const T& value )  
    {  
        // Add a key with given value  
        std::string v = T_as_string( value );  
        std::string key=in_key;  
        trim(key);  
        trim(v);  
        m_Contents[key] = v;  
        return;  
    }  

cpp檔案

// Config.cpp  

#include "Config.h"  

using namespace std;  


Config::Config( string filename, string delimiter,  
               string comment )  
               : m_Delimiter(delimiter), m_Comment(comment)  
{  
    // Construct a Config, getting keys and values from given file  

    std::ifstream in( filename.c_str() );  

    if( !in ) throw File_not_found( filename );   

    in >> (*this);  
}  


Config::Config()  
: m_Delimiter( string(1,'=') ), m_Comment( string(1,'#') )  
{  
    // Construct a Config without a file; empty  
}  



bool Config::KeyExists( const string& key ) const  
{  
    // Indicate whether key is found  
    mapci p = m_Contents.find( key );  
    return ( p != m_Contents.end() );  
}  


/* static */  
void Config::Trim( string& inout_s )  
{  
    // Remove leading and trailing whitespace  
    static const char whitespace[] = " \n\t\v\r\f";  
    inout_s.erase( 0, inout_s.find_first_not_of(whitespace) );  
    inout_s.erase( inout_s.find_last_not_of(whitespace) + 1U );  
}  


std::ostream& operator<<( std::ostream& os, const Config& cf )  
{  
    // Save a Config to os  
    for( Config::mapci p = cf.m_Contents.begin();  
        p != cf.m_Contents.end();  
        ++p )  
    {  
        os << p->first << " " << cf.m_Delimiter << " ";  
        os << p->second << std::endl;  
    }  
    return os;  
}  

void Config::Remove( const string& key )  
{  
    // Remove key and its value  
    m_Contents.erase( m_Contents.find( key ) );  
    return;  
}  

std::istream& operator>>( std::istream& is, Config& cf )  
{  
    // Load a Config from is  
    // Read in keys and values, keeping internal whitespace  
    typedef string::size_type pos;  
    const string& delim  = cf.m_Delimiter;  // separator  
    const string& comm   = cf.m_Comment;    // comment  
    const pos skip = delim.length();        // length of separator  

    string nextline = "";  // might need to read ahead to see where value ends  

    while( is || nextline.length() > 0 )  
    {  
        // Read an entire line at a time  
        string line;  
        if( nextline.length() > 0 )  
        {  
            line = nextline;  // we read ahead; use it now  
            nextline = "";  
        }  
        else  
        {  
            std::getline( is, line );  
        }  

        // Ignore comments  
        line = line.substr( 0, line.find(comm) );  

        // Parse the line if it contains a delimiter  
        pos delimPos = line.find( delim );  
        if( delimPos < string::npos )  
        {  
            // Extract the key  
            string key = line.substr( 0, delimPos );  
            line.replace( 0, delimPos+skip, "" );  

            // See if value continues on the next line  
            // Stop at blank line, next line with a key, end of stream,  
            // or end of file sentry  
            bool terminate = false;  
            while( !terminate && is )  
            {  
                std::getline( is, nextline );  
                terminate = true;  

                string nlcopy = nextline;  
                Config::Trim(nlcopy);  
                if( nlcopy == "" ) continue;  

                nextline = nextline.substr( 0, nextline.find(comm) );  
                if( nextline.find(delim) != string::npos )  
                    continue;  

                nlcopy = nextline;  
                Config::Trim(nlcopy);  
                if( nlcopy != "" ) line += "\n";  
                line += nextline;  
                terminate = false;  
            }  

            // Store key and value  
            Config::Trim(key);  
            Config::Trim(line);  
            cf.m_Contents[key] = line;  // overwrites if key is repeated  
        }  
    }  

    return is;  
}  
bool Config::FileExist(std::string filename)  
{  
    bool exist= false;  
    std::ifstream in( filename.c_str() );  
    if( in )   
        exist = true;  
    return exist;  
}  

void Config::ReadFile( string filename, string delimiter,  
                      string comment )  
{  
    m_Delimiter = delimiter;  
    m_Comment = comment;  
    std::ifstream in( filename.c_str() );  

    if( !in ) throw File_not_found( filename );   

    in >> (*this);  
} 

使用例項main.cpp

//main.cpp  
#include "Config.h"  
int main()  
{  
    int port;  
    std::string ipAddress;  
    std::string username;  
    std::string password;  
    const char ConfigFile[]= "config.txt";   
    Config configSettings(ConfigFile);  

    port = configSettings.Read("port", 0);  
    ipAddress = configSettings.Read("ipAddress", ipAddress);  
    username = configSettings.Read("username", username);  
    password = configSettings.Read("password", password);  
    std::cout<<"port:"<<port<<std::endl;  
    std::cout<<"ipAddress:"<<ipAddress<<std::endl;  
    std::cout<<"username:"<<username<<std::endl;  
    std::cout<<"password:"<<password<<std::endl;  

    return 0;  
}

config.txt的檔案內容：
ipAddress=10.10.90.125
port=3001
username=mark
password=2d2df5a

編譯執行輸出:
port:3001
ipAddress:10.10.90.125
username:mark
password:2d2df5a