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.
floatfield of the stream str to fixed as if by calling str.setf(std::ios_base::fixed, std::ios_base::floatfield)
floatfield of the stream str to scientific as if by calling str.setf(std::ios_base::scientific, std::ios_base::floatfield)
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.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).
| str | - | reference to I/O stream |
str (reference to the stream after manipulation).
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.
#include <iostream>
#include <iomanip>
#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
| changes floating-point precision (function) |
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