Simplifying FOR loops

Question

I have a function that essentially reads values in from a vector of doubles, appends these to a string (while ensuring a space between each and setting their precisions) and returns the end result, minus the final whitespace:

std::string MultiplePrintProperties::GetHpitchString()  
{    
    std::string str;  
    vector< double >::iterator it;    

    for ( it  = Vals.begin();    
          it != Vals.end();  
          it++ )  
    {
        ostringstream s;    

        // Set precision to 3 digits after the decimal point
        // and read into the string 
        boost::format fmt( "%.3f " ); 
        s << fmt % *( it );
        str.append( s.str() );      
    }

    // Remove last white space and return string   
    return str.substr( 0, str.length() - 1 ); 
}

I would like to find out if this code could be simplified in any way. I have recently been investigating the use of for_each and functors in particular but have not been able to figure out how these techniques could improve this particular example.

Answer 1

Since you're actually transforming doubles into strings, and appending these strings to a stringstream, you can use std::transform for that:

// your functor, transforming a double into a string
struct transform_one_double {
   std::string operator()( const double& d ) const {
     boost::format fmt( "%.3f " ); 
     return (fmt % d).str();
   }
};

// iteration code, taking each value and inserting the transformed
// value into the stringstream.
std::transform( vals.begin(), vals.end()
              , std::ostream_iterator<std::string>( s, " ")
              , transform_one_double() );