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)