Limit number of trailing zeros for fixed output

Question

I need help formatting output using C ++ streams. I would like to print numbers with a fixed decimal point and no more than two end places. I tried the following:

#include <iostream> #include <iomanip> using namespace std; int main(int argc, char **argv) { float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 }; std::cout << std::setprecision(2) << std::fixed; for(int i = 0; i < 6; ++i) { std::cout << testme[i] << std::endl; } return 0; } 

Output:

 0.12 1.23 12.35 123.45 1234.50 12345.00 

But I would like to have

 0.12 1.23 12.35 123.45 1234.5 12345 

Can I achieve this without using additional string manipulations?

Answer 1

It works ( http://ideone.com/CFcVhu ), but it is not so pretty ...

 #include <iostream> #include <iomanip> using namespace std; int main(int argc, char **argv) { float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 }; //std::cout << std::setprecision(2) << std::fixed; for(int i = 0; i < 6; ++i) { std::cout << ((int)(testme[i]*100.0))/100.0f << std::endl; } return 0; } 

Answer 2

I do not know a suitable manipulator, so you can use:

 #include <iostream> #include <iomanip> #include <cmath> template <typename T> struct Fixed { const T& value; const unsigned precision; const T significant; Fixed(const T& value, unsigned precision) : value(value), precision(precision), significant(std::pow(10, precision)) {} void write(std::ostream& stream) const { // Adjust stream settings std::ostream::char_type restore_fill = stream.fill('0'); std::ios_base::fmtflags restore_flags = stream.setf( std::ios_base::fixed, std::ios_base::floatfield); std::streamsize restore_precision = stream.precision(0); // Split the floating point into an integral and rounded fractional part T integral; unsigned long fractional = std::round(significant * std::modf(value, &integral)); // Determine the length of the fractional part unsigned digits = precision; while(fractional && fractional % 10 == 0) { fractional /= 10; --digits; } // Carry over to the integral part if( ! digits && fractional) { integral += 1; fractional = 0; } // Output stream << integral; if(fractional) { stream << '.' << std::setw(digits) << fractional; } // Restore stream settings stream.precision(restore_precision); stream.flags(restore_flags); stream.fill(restore_fill); } }; template <typename T> inline Fixed<T> fixed(const T& value, unsigned precision) { return Fixed<T>(value, precision); } template <typename T> inline std::ostream& operator << (std::ostream& stream, const Fixed<T>& value) { value.write(stream); return stream; } int main(int argc, char **argv) { float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 }; for(int i = 0; i < 6; ++i) { std::cout << fixed(testme[i], 2) << std::endl; } return 0; } 

Answer 3

In other words, you want to represent a number using two decimal digits if it is less than 1000 (is it always positive?), 1 decimal if it is less than 10000 and zero otherwise. Hmm, how can this be codified?