c++ - Round Double and Cast to String -


i suppose question follow previous question had regarding casting double string.

i have api i'm given string represents number. need round number 2 decimals of precision , return string. attempt follows:

void formatpercentcommon(std::string& percent, const std::string& value, config& config) {     double number = boost::lexical_cast<double>(value);     if (config.total == 0)     {         std::ostringstream err;         err << "cannot calculate percent 0 total.";         throw std::runtime_error(err.str());     }     number = (number/config.total)*100;     // format string return 2 decimals of precision     number = floor(number*100 + .5)/100;     percent = boost::lexical_cast<std::string>(number);      return; }

unfortunately cast captures "unrounded" values. (i.e. number = 30.63, percent = 30.629999999999) can suggest clean way round double , cast string 1 naturally want?

thanks in advance help. :)

streams usual formatting facility in c++. in case, stringstream trick:

std::ostringstream ss; ss << std::fixed << std::setprecision(2) << number; percent = ss.str();

you familiar setprecision previous post. fixed here used make precision affect number of digits after decimal point, instead of setting number of significant digits whole number.


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