foo=bar

light_pos  60.0    0.0   60.0
eye_pos    50.0   10.0   11.0
looking_at  0.0   15.0    0.0
near  20.0
far   80.0
angular_view_width  45.0

void Viewing_geometry::read_in_viewing_params( string file_name )
{
    ifstream config_file( file_name.c_str() );
    
    string line;              // We'll be reading in one line at a time,
    string temp_word;         // examining 1st word in that line.
    string temp_ascii_double; // This is for converting the numerical values to doubles.
    
    vector<double> vec; // We store the parameter's values in this vector.
    double temp_double;
    
    // Possible number separators are space or tab.
    const string delims( " \t" );
    
    // All the possible params that may be in the config.txt file, *in order*.
    vector<string> params;
    params.push_back( "light_pos" );
    params.push_back( "eye_pos" );
    params.push_back( "looking_at" );
    params.push_back( "near" );
    params.push_back( "far" );
    params.push_back( "angular_view_width" );
    
    while ( getline ( config_file, line ) ) // One line, 1 viewing parameter.
    {
        // Be sure to use string::size_type so we can safely compare to string:npos.
        string::size_type beg_idx, end_idx;
        
        beg_idx = line.find_first_not_of( delims ); // Starts at the beginning of the line.
        end_idx = line.find_first_of( delims, beg_idx ); // getting the first word in the line.
        if ( end_idx == string::npos ) // If we're on the last token in a line,
        {                              // set the end_idx appropriately
            end_idx = line.length();
        }
        
        // Get the name of the parameter.
        temp_word = line.substr( beg_idx, end_idx - beg_idx );
        
        // Make sure it's on our list. XXX Maybe change this to use a std algorithm.
        bool temp_word_found = false;
        // Compare temp_word to each word in our list of viable ones.
        for ( vector<string>::const_iterator it = params.begin();
              it != params.end();
              ++it )
        {
            // TODO Add ablility to have comments in the file starting with #.
            
            if ( temp_word == *it )
            {
                temp_word_found = true;
            }
        }
        
        if ( !temp_word_found )
        {
            cout << "WARNING: Couldn't find parameter " << temp_word <<
                    ". Moving on to next line in config.txt." << endl;
            continue;
        }
        
        // Go on to the first number after the descriptive word.
        beg_idx = line.find_first_not_of( delims, end_idx );
        
        // Traverse the rest of line.
        while ( beg_idx != string::npos )
        {
            end_idx = line.find_first_of( delims, beg_idx );
            if ( end_idx == string::npos )
            {
                end_idx = line.length();
            }
            
            // Ok. Now: beg_idx points to the beginning of the substring,
            // and end_idx points to one-past the end of it.
            //temp_ascii_double = string( line, beg_idx, end_idx - beg_idx ); or
            temp_ascii_double = line.substr( beg_idx, end_idx - beg_idx );
            temp_double = strtod( temp_ascii_double.c_str(), NULL );
            
            vec.push_back( temp_double );

            beg_idx = line.find_first_not_of( delims, end_idx );
        }
        // Ok, vec is full. Figure out which param it corresponds to,
        // and copy the values.
                
        
        // I don't yet see a better way to do this... (?) XXX
        if ( temp_word == "light_pos" )
        {
            //cout << "Setting light position: " <<
            //    vec[0] << " " << vec[1] << " " << vec[2] << endl;
            d_light_pos.d_x = vec[0];
            d_light_pos.d_y = vec[1];
            d_light_pos.d_z = vec[2];
        }
                        
        if ( temp_word == "eye_pos" )
        {
            //cout << "Setting eye position: " <<
            //    vec[0] << " " << vec[1] << " " << vec[2] << endl;
            d_eye_pos.d_x = vec[0];
            d_eye_pos.d_y = vec[1];
            d_eye_pos.d_z = vec[2];
        }
                        
        if ( temp_word == "looking_at" )
        {
            //cout << "Setting looking-at position: " <<
            //    vec[0] << " " << vec[1] << " " << vec[2] << endl;
            d_looking_at.d_x = vec[0];
            d_looking_at.d_y = vec[1];
            d_looking_at.d_z = vec[2];
        }
                        
        if ( temp_word == "near" )
        {
            //cout << "Setting near: " << vec[0] << endl;
            d_near = vec[0];
        }
                        
        if ( temp_word == "far" )
        {
            //cout << "Setting far: " << vec[0] << endl;
            d_far = vec[0];
        }
                        
        if ( temp_word == "angular_view_width" )
        {
            //cout << "Setting angular view width (in file): " << vec[0] << endl;
            d_angular_view_width = vec[0];
            // ...but don't forget to convert to radians, which we use
            // exclusively in the code.
            d_angular_view_width = d_angular_view_width * PI / 180.0;
            cout << "and setting d_angular_view_width: " << d_angular_view_width << endl;
        }
                        
        vec.clear();
        // Now on to the next line.
    }
}