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

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library(C++20)

Diagnostics library

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)

Atomic operations library(C++11)

Thread support library(C++11)

Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated in C++98)

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

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

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_flushno_emit_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.

Example

Run this code

#include <iostream>#include <iomanip>#include <sstream>   enumclass cap { title, middle, end };void print(constchar* 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)