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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

Input/output manipulators

Floating-point formatting
showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
Integer formatting
setbase showbasenoshowbase	dechexoct
Boolean formatting
boolalphanoboolalpha
Field width and fill control
setfill setw	internalleftright
Other formatting
showposnoshowpos	uppercasenouppercase
Whitespace processing
ws ends	skipwsnoskipws
Output flushing
flush endl flush_emit (C++20)	unitbufnounitbuf emit_on_flushnoemit_on_flush (C++20)(C++20)
Status flags manipulation
resetiosflags	setiosflags
Time and money I/O
get_money (C++11) get_time (C++11)	put_money (C++11) put_time (C++11)
Quoted manipulator
quoted (C++14)

 

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 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.

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 <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

See also

setprecision

changes floating-point precision (function)