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

On 1/16/2013 2:47 AM, Chris Stankevitz wrote:

On Tue, Jan 15, 2013 at 5:49 PM, Steve Lorimer 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(); }

Have you looked at boost spirit's karma lib? IIRC, it outperforms most other libs with formatted output like this. Jeff