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std::fixed, std::scientific, std::hexfloat, std::defaultfloat

From cppreference.com
< cpp‎ | io‎ | manip
 
 
 
Input/output manipulators
Floating-point formatting
fixedscientifichexfloatdefaultfloat
(C++11)(C++11)
Integer formatting
Boolean formatting
Field width and fill control
Other formatting
Whitespace processing
Output flushing
Status flags manipulation
Time and money I/O
(C++11)
(C++11)
(C++11)
(C++11)
Quoted manipulator
(C++14)
 
Defined in header <ios>
(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 input/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.

[edit] Example

#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);
 
    double f;
    std::istringstream("0x1P-1022") >> std::hexfloat >> f;
    std::cout << "Parsing 0x1P-1022 as hex 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 0x1P-1022 as hex gives 0

[edit] See also

changes floating-point precision
(function) [edit]