[转载]config文件的一个很好的实现

以下是转载于网上的一个很好的config文件的实现，留存以备案

 //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("") || 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;
 }

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

         // Ignore comments
         line = line.substr( , 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( , delimPos );
             line.replace( , 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( , 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);
 }

 //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", );
     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 ;
 }

config.txt的文件内容： 
ipAddress=10.10.90.125 
port=3001 
username=mark 
password=2d2df5a

编译运行输出: 
port:3001 
ipAddress:10.10.90.125 
username:mark 
password:2d2df5a

原文地址：http://cooker.iteye.com/blog/777455