Habe auf http://www-personal.umich.edu/~wagnerr/ConfigFile.html ein Klasse gefunden die Konfigurationsdateien ließt, verändern und schreiben soll.

ConfigFile.cpp:

#include "ConfigFile.h"

using std::string;

ConfigFile::ConfigFile( string filename, string delimiter,
                        string comment, string sentry )
	: myDelimiter(delimiter), myComment(comment), mySentry(sentry)
{
	// Construct a ConfigFile, getting keys and values from given file

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

	if( !in ) throw file_not_found( filename ); 

	in >> (*this);
}

ConfigFile::ConfigFile()
	: myDelimiter( string(1,'=') ), myComment( string(1,'#') )
{
	// Construct a ConfigFile without a file; empty
}

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

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

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

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

std::istream& operator>>( std::istream& is, ConfigFile& cf )
{
	// Load a ConfigFile from is
	// Read in keys and values, keeping internal whitespace
	typedef string::size_type pos;
	const string& delim  = cf.myDelimiter;  // separator
	const string& comm   = cf.myComment;    // comment
	const string& sentry = cf.mySentry;     // end of file sentry
	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) );

		// Check for end of file sentry
		if( sentry != "" && line.find(sentry) != string::npos ) return is;

		// 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;
				ConfigFile::trim(nlcopy);
				if( nlcopy == "" ) continue;

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

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

			// Store key and value
			ConfigFile::trim(key);
			ConfigFile::trim(line);
			cf.myContents[key] = line;  // overwrites if key is repeated
		}
	}

	return is;
}

ConfigFile.h

// Typical usage
// -------------
// 
// Given a configuration file "settings.inp":
//   atoms  = 25
//   length = 8.0  # nanometers
//   name = Reece Surcher
// 
// Named values are read in various ways, with or without default values:
//   ConfigFile config( "settings.inp" );
//   int atoms = config.read<int>( "atoms" );
//   double length = config.read( "length", 10.0 );
//   string author, title;
//   config.readInto( author, "name" );
//   config.readInto( title, "title", string("Untitled") );
// 
// See file example.cpp for more examples.

#ifndef CONFIGFILE_H
#define CONFIGFILE_H

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

using std::string;

class ConfigFile {
// Data
protected:
	string myDelimiter;  // separator between key and value
	string myComment;    // separator between value and comments
	string mySentry;     // optional string to signal end of file
	std::map<string,string> myContents;  // extracted keys and values

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

// Methods
public:
	ConfigFile( string filename,
	            string delimiter = "=",
	            string comment = "#",
				string sentry = "EndConfigFile" );
	ConfigFile();

	// Search for key and read value or optional default value
	template<class T> T read( const string& key ) const;  // call as read<T>
	template<class T> T read( const string& key, const T& value ) const;
	template<class T> bool readInto( T& var, const string& key ) const;
	template<class T>
	bool readInto( T& var, const string& key, const T& value ) const;

	// Modify keys and values
	template<class T> void add( string key, const T& value );
	void remove( const string& key );

	// Check whether key exists in configuration
	bool keyExists( const string& key ) const;

	// Check or change configuration syntax
	string getDelimiter() const { return myDelimiter; }
	string getComment() const { return myComment; }
	string getSentry() const { return mySentry; }
	string setDelimiter( const string& s )
		{ string old = myDelimiter;  myDelimiter = s;  return old; }  
	string setComment( const string& s )
		{ string old = myComment;  myComment = s;  return old; }

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

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

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

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

/* static */
template<>
inline bool ConfigFile::string_as_T<bool>( const 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;
	string sup = s;
	for( string::iterator p = sup.begin(); p != sup.end(); ++p )
		*p = toupper(*p);  // make string all caps
	if( sup==string("FALSE") || sup==string("F") ||
	    sup==string("NO") || sup==string("N") ||
	    sup==string("0") || sup==string("NONE") )
		b = false;
	return b;
}

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

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

template<class T>
bool ConfigFile::readInto( T& var, const 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 = myContents.find(key);
	bool found = ( p != myContents.end() );
	if( found ) var = string_as_T<T>( p->second );
	return found;
}

template<class T>
bool ConfigFile::readInto( T& var, const 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 = myContents.find(key);
	bool found = ( p != myContents.end() );
	if( found )
		var = string_as_T<T>( p->second );
	else
		var = value;
	return found;
}

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

#endif  // CONFIGFILE_H

triplet.h

#include <iostream>

struct Triplet
{
	int a, b, c;

	Triplet() {}
	Triplet( int u, int v, int w ) : a(u), b(v), c(w) {}
	Triplet( const Triplet& orig ) : a(orig.a), b(orig.b), c(orig.c) {}

	Triplet& operator=( const Triplet& orig )
		{ a = orig.a;  b = orig.b;  c = orig.c;  return *this; }
};

std::ostream& operator<<( std::ostream& os, const Triplet& t )
{
	// Save a triplet to os
	os << t.a << " " << t.b << " " << t.c;
	return os;
}

std::istream& operator>>( std::istream& is, Triplet& t )
{
	// Load a triplet from is
	is >> t.a >> t.b >> t.c;
	return is;
}

Der Autor hat leider kein Beispiel zur Sicherung der veränderten Datei.

Habe dann mit Hilfe von dieser Seite:

ofstream file;
file.open ("test.conf");
file << config;

, diesen Code zum speichern verwendet.

Mein Problem ist jetzt das in der ursprünglichen Konfigurationsdatei noch Kommentare stehen (#test), die jetzt beim auslesen und überschreiben der Datei verloren gehen. Die Kommentare sollen aber erhalten bleiben, weiß aber nicht wie ich den Code so verändern kann.

Kann mir jemand dabei helfen?

Danke und Gruß
nihilfire

Mein Problem ist jetzt das in der ursprünglichen Konfigurationsdatei noch Kommentare stehen (#test), die jetzt beim auslesen und überschreiben der Datei verloren gehen. Die Kommentare sollen aber erhalten bleiben, weiß aber nicht wie ich den Code so verändern kann.

Das ist in diesem Code gar nicht vorgesehen.
Und die Kommentare ordentlich und konsistent zu den Werten zu erhalten, ist auch keine einfache Sache. Und auch gar nicht allgemein lösbar. Ich kann nur davon abraten.