Difference between revisions of "cpp/io/manip/fixed"
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(→Notes: note that these manipulators don't affect parsing, current msvc stl is buggy) |
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===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. | ||
===Example=== | ===Example=== | ||
Revision as of 22:24, 6 April 2022
| 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.
Contents |
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
| changes floating-point precision (function) |
