std::fixed, std::scientific, std::hexfloat, std::defaultfloat
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Input/output manipulators
Floating-point formatting
fixedscientifichexfloatdefaultfloat
(C++11)(C++11)
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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 ).
Contents
[edit] Parameters
str
-
reference to I/O stream
[edit] Return value
str (reference to the stream after manipulation).
[edit] 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.
[edit] 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