Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/io/manip/fixed"

From cppreference.com
< cpp‎ | io‎ | manip
m (fmt)
m (→‎Example: fmt a bit more.)
 
(11 intermediate revisions by 8 users not shown)
Line 3: Line 3:
 
{{dcl begin}}
 
{{dcl begin}}
 
{{dcl header|ios}}
 
{{dcl header|ios}}
−
{{dcl | num = 1|
+
{{dcl|num=1|
 
std::ios_base& fixed( std::ios_base& str );
 
std::ios_base& fixed( std::ios_base& str );
 
}}
 
}}
−
{{dcl | num = 2|
+
{{dcl|num=2|
 
std::ios_base& scientific( std::ios_base& str );
 
std::ios_base& scientific( std::ios_base& str );
 
}}
 
}}
−
{{dcl | num = 3 | since=c++11 |
+
{{dcl|num=3|since=c++11|
 
std::ios_base& hexfloat( std::ios_base& str );
 
std::ios_base& hexfloat( std::ios_base& str );
 
}}
 
}}
−
{{dcl | num = 4 | since=c++11 |
+
{{dcl|num=4|since=c++11|
 
std::ios_base& defaultfloat( std::ios_base& str );
 
std::ios_base& defaultfloat( std::ios_base& str );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Modifies the default formatting for floating-point input/output.
+
Modifies the default formatting for floating-point output.
  
−
@1@ Sets the {{tt|floatfield}} of the stream {{tt|str}} to {{tt|fixed}} as if by calling {{c|str.setf(std::ios_base::fixed, std::ios_base::floatfield)}}
+
@1@ Sets the {{tt|floatfield}} of the stream {{c|str}} to {{tt|fixed}} as if by calling {{c|str.setf(std::ios_base::fixed, std::ios_base::floatfield)}}.
  
−
@2@ Sets the {{tt|floatfield}} of the stream {{tt|str}} to {{tt|scientific}} as if by calling {{c|str.setf(std::ios_base::scientific, std::ios_base::floatfield)}}
+
@2@ Sets the {{tt|floatfield}} of the stream {{c|str}} to {{tt|scientific}} as if by calling {{c|str.setf(std::ios_base::scientific, std::ios_base::floatfield)}}.
  
−
@3@ Sets the {{tt|floatfield}} of the stream {{tt|str}} to {{tt|fixed}} and {{tt|scientific}} simultaneously as if by calling {{c|str.setf(std::ios_base::fixed {{!}} std::ios_base::scientific, std::ios_base::floatfield)}}. This enables hexadecimal floating-point formatting.
+
@3@ Sets the {{tt|floatfield}} of the stream {{c|str}} to {{tt|fixed}} and {{tt|scientific}} simultaneously as if by calling {{c|str.setf(std::ios_base::fixed {{!}} std::ios_base::scientific, std::ios_base::floatfield)}}. This enables hexadecimal floating-point formatting.
  
−
@4@ Sets the {{tt|floatfield}} of the stream {{tt|str}} to zero, as if by calling {{c|str.unsetf(std::ios_base::floatfield)}}. This enables the default floating-point formatting, which is different from fixed and scientific.
+
@4@ Sets the {{tt|floatfield}} of the stream {{c|str}} to zero, as if by calling {{c|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 {{c|out << std::fixed}} for any {{tt|out}} of type {{lc|std::basic_ostream}} or with an expression such as {{c|in >> std::scientific}} for any {{tt|in}} of type {{lc|std::basic_istream}}.
+
This is an I/O manipulator, it may be called with an expression such as {{c|out << std::fixed}} for any {{tt|out}} of type {{lc|std::basic_ostream}} (or with an expression such as {{c|in >> std::scientific}} for any {{tt|in}} of type {{lc|std::basic_istream}}).
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | str | reference to I/O stream }}
+
{{par|str|reference to I/O stream}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
 
+
{{c|str}} (reference to the stream after manipulation).
−
{{tt|str}} (reference to the stream after manipulation)
+
  
 
===Notes===
 
===Notes===
−
Hexadecimal floating-point formatting in existing implementations ignores the stream precision specification, despite being formally specified by {{lc|std::num_put::do_put}}. This is [http://open-std.org/JTC1/SC22/WG21/docs/lwg-defects.html#671 LWG 671].
+
Hexadecimal floating-point formatting ignores the stream precision specification, as required by the specification of {{lc|std::num_put::do_put}}.
 +
 
 +
These manipulators do not affect floating-point parsing.
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|
+
|code=
−
| code=
+
#include <iomanip>
 
#include <iostream>
 
#include <iostream>
 
#include <sstream>
 
#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()
 
int main()
 
{
 
{
−
     std::cout << "The number 0.01 in fixed:      " << std::fixed << 0.01 << '\n'
+
     print("0.0", 0.0, cap::title);
−
              << "The number 0.01 in scientific: " << std::scientific << 0.01 << '\n'
+
    print("0.01", 0.01, cap::middle);
−
              << "The number 0.01 in hexfloat:   " << std::hexfloat << 0.01 << '\n'
+
    print("0.00001", 0.00001, cap::end);
−
              << "The number 0.01 in default:   " << std::defaultfloat << 0.01 << '\n';
+
 
 +
    // Note; choose clang for correct output
 
     double f;
 
     double f;
−
     std::istringstream("0x1P-1022") >> std::hexfloat >> f;
+
     std::istringstream("0x1.8p+0") >> f;
−
     std::cout << "Parsing 0x1P-1022 as hex gives " << f << '\n';
+
    std::cout << "Parsing 0x1.8p+0 gives " << f << '\n';
 +
 
 +
    std::istringstream("0x1P-1022") >> f;
 +
     std::cout << "Parsing 0x1P-1022 gives " << f << '\n';
 
}
 
}
−
| output=
+
|output=
−
The number 0.01 in fixed:     0.010000
+
┌──────────┬────────────┬──────────────────────────┐
−
The number 0.01 in scientific: 1.000000e-02
+
│  number │  iomanip  │      representation      │
−
The number 0.01 in hexfloat:   0x1.47ae147ae147bp-7
+
├──────────┼────────────┼──────────────────────────┤
−
The number 0.01 in default:   0.01
+
│ 0.0      │ fixed      │ 0.000000                │
−
Parsing 0x1P-1022 as hex gives 2.22507e-308
+
│ 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===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/io/manip/dsc setprecision}}
+
{{dsc inc|cpp/io/manip/dsc setprecision}}
 
{{dsc end}}
 
{{dsc end}}
  
−
[[de:cpp/io/manip/fixed]]
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
[[es:cpp/io/manip/fixed]]
+
−
[[fr:cpp/io/manip/fixed]]
+
−
[[it:cpp/io/manip/fixed]]
+
−
[[ja:cpp/io/manip/fixed]]
+
−
[[pt:cpp/io/manip/fixed]]
+
−
[[ru:cpp/io/manip/fixed]]
+
−
[[zh:cpp/io/manip/fixed]]
+

Latest revision as of 10:08, 16 September 2023

 
C++
 
Input/output library
 
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
(C++20)  

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 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.

These manipulators do not affect floating-point parsing.

[edit] 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

[edit] See also

 changes floating-point precision
(function) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/io/manip/fixed&oldid=159201"