Re: [Boost-users] Why is boost::format::operator% not declared const?

Subject: Re: [Boost-users] Why is boost::format::operator% not declared const?
From: Chris Stankevitz (chrisstankevitz_at_[hidden])
Date: 2013-01-16 02:47:47

On Tue, Jan 15, 2013 at 5:49 PM, Steve Lorimer <steve.lorimer_at_[hidden]> wrote:
> Think about what happens if you feed multiple elements via operator% and
> then call .str() - you get a std::string back - it has to store everything
> you've fed in internally so that you can access the formatted string later
> via .str()

Steve,

Thank you.  I never used boost::format::str, but I agree that its
presence indicates that operator% must alter an internal state.

Question 1: Is there an efficient way to do the following (and by
"more efficient" I mean fewer format constructors and string parsing):

void WriteLog(float x, float y, float z, const Employee& e)
{
  std::cout
    << "Values: "
    << boost::format("%0.3") % x
    << e
    << boost::format("%0.3") % y
    << boost::format("%0.3") % z;
}

Question 2:  Is there a more efficient way to do this:

std::string FloatToString(float x, int DigitsAfterDecimal)
{
  std::ostringstream FormatStream;

  FormatStream << "%0." << DigitsAfterDecimal;

  boost::format Formatter(FormatStream.str());

  Formatter % x;

  return Formatter.str();
}

Thank you,

Chris