Difference between revisions of "cpp/numeric/fenv/feround"
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{{cpp/numeric/fenv/navbar}} | {{cpp/numeric/fenv/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | cfenv}} | + | {{dcl header|cfenv}} |
| − | {{dcl | | + | {{dcl|since=c++11|num=1| |
int fesetround( int round ) | int fesetround( int round ) | ||
}} | }} | ||
| − | {{dcl | | + | {{dcl|since=c++11|num=2| |
int fegetround() | int fegetround() | ||
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===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | round | rounding direction, one of [[cpp/numeric/fenv/FE_round|floating point rounding macros]]}} | + | {{par|round|rounding direction, one of [[cpp/numeric/fenv/FE_round|floating point rounding macros]]}} |
{{par end}} | {{par end}} | ||
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1) {{c|0}} on success, non-zero otherwise. | 1) {{c|0}} on success, non-zero otherwise. | ||
| − | 2) | + | 2) The [[cpp/numeric/fenv/FE_round|floating point rounding macro]] describing the current rounding direction or a negative value if the direction cannot be determined. |
| + | |||
| + | ===Notes=== | ||
| + | The current rounding mode, reflecting the effects of the most recent {{tt|fesetround}}, can also be queried with {{lc|FLT_ROUNDS}}. | ||
| + | |||
| + | See [[cpp/numeric/fenv/FE_round|floating-point rounding macros]] for the effects of rounding. | ||
===Example=== | ===Example=== | ||
| − | {{include| cpp/numeric/math/example_nearbyint}} | + | {{include|cpp/numeric/math/example_nearbyint}} |
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/numeric/math/dsc nearbyint}} | + | {{dsc inc|cpp/numeric/math/dsc nearbyint}} |
| − | {{dsc inc | cpp/numeric/math/dsc rint}} | + | {{dsc inc|cpp/numeric/math/dsc rint}} |
| + | {{dsc see c|c/numeric/fenv/feround|fegetround|fesetround}} | ||
{{dsc end}} | {{dsc end}} | ||
| − | + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | |
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Latest revision as of 09:36, 25 April 2023
| Defined in header <cfenv>
|
||
| int fesetround( int round ) |
(1) | (since C++11) |
| int fegetround() |
(2) | (since C++11) |
Manages the floating-point rounding direction.
1) Attempts to establish the floating-point rounding direction equal to the argument
round, which is expected to be one of the floating point rounding macros. 2) Returns the value of the floating point rounding macro that corresponds to the current rounding direction.
Contents |
[edit] Parameters
| round | - | rounding direction, one of floating point rounding macros |
[edit] Return value
1) 0 on success, non-zero otherwise.
2) The floating point rounding macro describing the current rounding direction or a negative value if the direction cannot be determined.
[edit] Notes
The current rounding mode, reflecting the effects of the most recent fesetround, can also be queried with FLT_ROUNDS.
See floating-point rounding macros for the effects of rounding.
[edit] Example
Run this code
#include <cfenv> #include <cmath> #include <iomanip> #include <iostream> #include <utility> // #pragma STDC FENV_ACCESS ON int main() { static constexpr std::pair<const char*, const double> samples[] { {" 12.0", 12.0}, {" 12.1", 12.1}, {"-12.1", -12.1}, {" 12.5", 12.5}, {"-12.5", -12.5}, {" 12.9", 12.9}, {"-12.9", -12.9}, {" 13.0", 13.0} }; std::cout << "│ sample │ FE_DOWNWARD │ FE_UPWARD │ FE_TONEAREST │ FE_TOWARDZERO │\n"; for (const auto& [str, fp] : samples) { std::cout << "│ " << std::setw(6) << str << " │ "; for (const int dir : {FE_DOWNWARD, FE_UPWARD, FE_TONEAREST, FE_TOWARDZERO}) { std::fesetround(dir); std::cout << std::setw(10) << std::fixed << std::nearbyint(fp) << " │ "; } std::cout << '\n'; } }
Output:
│ sample │ FE_DOWNWARD │ FE_UPWARD │ FE_TONEAREST │ FE_TOWARDZERO │ │ 12.0 │ 12.000000 │ 12.000000 │ 12.000000 │ 12.000000 │ │ 12.1 │ 12.000000 │ 13.000000 │ 12.000000 │ 12.000000 │ │ -12.1 │ -13.000000 │ -12.000000 │ -12.000000 │ -12.000000 │ │ 12.5 │ 12.000000 │ 13.000000 │ 12.000000 │ 12.000000 │ │ -12.5 │ -13.000000 │ -12.000000 │ -12.000000 │ -12.000000 │ │ 12.9 │ 12.000000 │ 13.000000 │ 13.000000 │ 12.000000 │ │ -12.9 │ -13.000000 │ -12.000000 │ -13.000000 │ -12.000000 │ │ 13.0 │ 13.000000 │ 13.000000 │ 13.000000 │ 13.000000 │
[edit] See also
| (C++11)(C++11)(C++11) |
nearest integer using current rounding mode (function) |
| (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) |
nearest integer using current rounding mode with exception if the result differs (function) |
| C documentation for fegetround, fesetround
| |
