Difference between revisions of "cpp/io/manip/fixed"
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(Note unparsable hex floats, make it a little clearer that these manipulators don't affect default parsing) |
m (→Example: fmt a bit more.) |
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| 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 ); | ||
}} | }} | ||
| Line 19: | Line 19: | ||
Modifies the default formatting for floating-point output. | Modifies the default formatting for floating-point output. | ||
| − | @1@ Sets the {{tt|floatfield}} of the stream {{ | + | @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 {{ | + | @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 {{ | + | @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 {{ | + | @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}}). | ||
| Line 31: | Line 31: | ||
===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). | |
| − | {{ | + | |
===Notes=== | ===Notes=== | ||
Hexadecimal floating-point formatting ignores the stream precision specification, as required by the specification of {{lc|std::num_put::do_put}}. | 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 | + | These manipulators do not affect floating-point parsing. |
===Example=== | ===Example=== | ||
{{example | {{example | ||
| − | + | |code= | |
| − | + | ||
| − | + | ||
#include <iomanip> | #include <iomanip> | ||
| + | #include <iostream> | ||
#include <sstream> | #include <sstream> | ||
enum class cap { title, middle, end }; | enum class cap { title, middle, end }; | ||
| + | |||
void print(const char* text, double num, cap c) | void print(const char* text, double num, cap c) | ||
{ | { | ||
| − | if (c == cap::title) std::cout << | + | if (c == cap::title) |
| − | + | std::cout << | |
| − | + | "┌──────────┬────────────┬──────────────────────────┐\n" | |
| − | + | "│ number │ iomanip │ representation │\n" | |
| − | + | "├──────────┼────────────┼──────────────────────────┤\n"; | |
std::cout << std::left | 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 ? | std::cout << (c != cap::end ? | ||
| − | + | "├──────────┼────────────┼──────────────────────────┤\n" : | |
| − | + | "└──────────┴────────────┴──────────────────────────┘\n"); | |
} | } | ||
| Line 80: | Line 78: | ||
print("0.00001", 0.00001, cap::end); | print("0.00001", 0.00001, cap::end); | ||
| + | // Note; choose clang for correct output | ||
double f; | double f; | ||
std::istringstream("0x1.8p+0") >> f; | std::istringstream("0x1.8p+0") >> f; | ||
std::cout << "Parsing 0x1.8p+0 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= | |
┌──────────┬────────────┬──────────────────────────┐ | ┌──────────┬────────────┬──────────────────────────┐ | ||
│ number │ iomanip │ representation │ | │ number │ iomanip │ representation │ | ||
| Line 103: | Line 105: | ||
│ 0.00001 │ default │ 1e-05 │ | │ 0.00001 │ default │ 1e-05 │ | ||
└──────────┴────────────┴──────────────────────────┘ | └──────────┴────────────┴──────────────────────────┘ | ||
| − | Parsing 0x1.8p+0 gives | + | 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}} | ||
{{langlinks|de|es|fr|it|ja|pt|ru|zh}} | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Latest revision as of 10:08, 16 September 2023
| 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 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) |
