std::fixed,std::scientific,std::hexfloat,std::defaultfloat(3)

NAME
std::fixed,std::scientific,std::hexfloat,std::defaultfloat - std::fixed,std::scientific,std::hexfloat,std::defaultfloat

Synopsis
   Defined in header <ios>
   std::ios_base& fixed( std::ios_base& str ); (1)
   std::ios_base& scientific( std::ios_base& str ); (2)
   std::ios_base& hexfloat( std::ios_base& str ); (3) (since C++11)
   std::ios_base& defaultfloat( std::ios_base& str ); (4) (since C++11)
   Modifies the default formatting for floating-point output.
   1) Sets the floatfield of the stream str to fixed as if by calling
   str.setf(std::ios_base::fixed, std::ios_base::floatfield).
   2) Sets the floatfield of the stream str to scientific as if by calling
   str.setf(std::ios_base::scientific, std::ios_base::floatfield).
   3) Sets the floatfield of the stream str to fixed and scientific simultaneously as
   if by calling str.setf(std::ios_base::fixed | std::ios_base::scientific,
   std::ios_base::floatfield). This enables hexadecimal floating-point formatting.
   4) Sets the floatfield of the stream str to zero, as if by calling
   str.unsetf(std::ios_base::floatfield). This enables the default floating-point
   formatting, which is different from fixed and scientific.
   This is an I/O manipulator, it may be called with an expression such as out <<
   std::fixed for any out of type std::basic_ostream (or with an expression such as in
   >> std::scientific for any in of type std::basic_istream).

Parameters
   str - reference to I/O stream

Return value
   str (reference to the stream after manipulation).

Notes
   Hexadecimal floating-point formatting ignores the stream precision specification, as
   required by the specification of std::num_put::do_put.
   These manipulators do not affect floating-point parsing.

Example
// Run this code
 #include <iomanip>
 #include <iostream>
 #include <sstream>
 enum class cap { title, middle, end };
 void print(const char* text, double num, cap c)
 {
     if (c == cap::title)
         std::cout <<
             "┌──────────┬────────────┬──────────────────────────┐\n"
             "│ number │ iomanip │ representation │\n"
             "├──────────┼────────────┼──────────────────────────┤\n";
     std::cout << std::left
          << "│ " << std::setw(8) << text << " │ fixed │ "
          << std::setw(24) << std::fixed << num << " │\n"
          << "│ " << std::setw(8) << text << " │ scientific │ "
          << std::setw(24) << std::scientific << num << " │\n"
          << "│ " << std::setw(8) << text << " │ hexfloat │ "
          << std::setw(24) << std::hexfloat << num << " │\n"
          << "│ " << std::setw(8) << text << " │ default │ "
          << std::setw(24) << std::defaultfloat << num << " │\n";
     std::cout << (c != cap::end ?
             "├──────────┼────────────┼──────────────────────────┤\n" :
             "└──────────┴────────────┴──────────────────────────┘\n");
 }
 int main()
 {
     print("0.0", 0.0, cap::title);
     print("0.01", 0.01, cap::middle);
     print("0.00001", 0.00001, cap::end);
     // Note; choose clang for correct output
     double f;
     std::istringstream("0x1.8p+0") >> f;
     std::cout << "Parsing 0x1.8p+0 gives " << f << '\n';
     std::istringstream("0x1P-1022") >> f;
     std::cout << "Parsing 0x1P-1022 gives " << f << '\n';
 }

Output:
 ┌──────────┬────────────┬──────────────────────────┐
 │ number │ iomanip │ representation │
 ├──────────┼────────────┼──────────────────────────┤
 │ 0.0 │ fixed │ 0.000000 │
 │ 0.0 │ scientific │ 0.000000e+00 │
 │ 0.0 │ hexfloat │ 0x0p+0 │
 │ 0.0 │ default │ 0 │
 ├──────────┼────────────┼──────────────────────────┤
 │ 0.01 │ fixed │ 0.010000 │
 │ 0.01 │ scientific │ 1.000000e-02 │
 │ 0.01 │ hexfloat │ 0x1.47ae147ae147bp-7 │
 │ 0.01 │ default │ 0.01 │
 ├──────────┼────────────┼──────────────────────────┤
 │ 0.00001 │ fixed │ 0.000010 │
 │ 0.00001 │ scientific │ 1.000000e-05 │
 │ 0.00001 │ hexfloat │ 0x1.4f8b588e368f1p-17 │
 │ 0.00001 │ default │ 1e-05 │
 └──────────┴────────────┴──────────────────────────┘
 Parsing 0x1.8p+0 gives 1.5
 Parsing 0x1P-1022 gives 2.22507e-308

See also
   setprecision changes floating-point precision
                (function)