C++编写Config类读取配置文件

//Config.h#pragma once#include <string>#include <map>#include <iostream>#include <fstream>#include <sstream>/** \brief Generic configuration Class**/class Config {// Dataprotected:std::string m_Delimiter;  //!< separator between key and valuestd::string m_Comment;    //!< separator between value and commentsstd::map<std::string,std::string> m_Contents;  //!< extracted keys and valuestypedef std::map<std::string,std::string>::iterator mapi;typedef std::map<std::string,std::string>::const_iterator mapci;// Methodspublic: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 configurationbool KeyExists( const std::string& in_key ) const;// Modify keys and valuestemplate<class T> void Add( const std::string& in_key, const T& in_value );void Remove( const std::string& in_key );// Check or change configuration syntaxstd::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 configurationfriend 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 typespublic: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 << operatorstd::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 >> operatorT 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 nothingreturn 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 truebool b = true;std::string sup = s;for( std::string::iterator p = sup.begin(); p != sup.end(); ++p )*p = toupper(*p);  // make string all capsif( 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 keymapci 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 foundmapci 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 untouchedmapci 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 defaultmapci p = m_Contents.find(key);bool found = ( p != m_Contents.end() );if( found )var = string_as_T<T>( p->second );elsevar = value;return found;}template<class T>void Config::Add( const std::string& in_key, const T& value ){// Add a key with given valuestd::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 filestd::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 foundmapci p = m_Contents.find( key );return ( p != m_Contents.end() );}/* static */void Config::Trim( string& inout_s ){// Remove leading and trailing whitespacestatic 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 osfor( 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 valuem_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 whitespacetypedef string::size_type pos;const string& delim  = cf.m_Delimiter;  // separatorconst string& comm   = cf.m_Comment;    // commentconst pos skip = delim.length();        // length of separatorstring nextline = "";  // might need to read ahead to see where value endswhile( is || nextline.length() > 0 ){// Read an entire line at a timestring line;if( nextline.length() > 0 ){line = nextline;  // we read ahead; use it nownextline = "";}else{std::getline( is, line );}// Ignore commentsline = line.substr( 0, line.find(comm) );// Parse the line if it contains a delimiterpos delimPos = line.find( delim );if( delimPos < string::npos ){// Extract the keystring 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 sentrybool 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 valueConfig::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", 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

参考： http://cooker.iteye.com/blog/777455