From cppreference.com
Defined in header
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
(or with an expression such as in>>std::scientific for any in of type
).
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
.
These manipulators do not affect floating-point parsing.
Example
Run this code
#include<iomanip>#include<iostream>#include<sstream>enumclasscap{title,middle,end};voidprint(constchar*text,doublenum,capc){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");}intmain(){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 outputdoublef;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