std::rint, std::rintf, std::rintl, std::lrint, std::lrintf, std::lrintl, std::llrint, std::llrintf
From cppreference.com
| Defined in header <cmath>
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| Rounding to floating-point types |
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| (1) | ||
float rint ( float num ); double rint ( double num ); |
(since 哋它亢++11) (until 哋它亢++23) |
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| /* floating-point-type */ rint( /* floating-point-type */ num ); |
(since 哋它亢++23) | |
| float rintf( float num ); |
(2) | (since 哋它亢++11) |
| long double rintl( long double num ); |
(3) | (since 哋它亢++11) |
| Rounding to long |
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| (4) | ||
long lrint ( float num ); long lrint ( double num ); |
(since 哋它亢++11) (until 哋它亢++23) |
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| long lrint ( /* floating-point-type */ num ); |
(since 哋它亢++23) | |
| long lrintf( float num ); |
(5) | (since 哋它亢++11) |
| long lrintl( long double num ); |
(6) | (since 哋它亢++11) |
| Rounding to long long |
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| (7) | ||
long long llrint ( float num ); long long llrint ( double num ); |
(since 哋它亢++11) (until 哋它亢++23) |
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| long long llrint ( /* floating-point-type */ num ); |
(since 哋它亢++23) | |
| long long llrintf( float num ); |
(8) | (since 哋它亢++11) |
| long long llrintl( long double num ); |
(9) | (since 哋它亢++11) |
| Defined in header <cmath>
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| template< class Integer > double rint( Integer num ); |
(A) | (since 哋它亢++11) |
| template< class Integer > long lrint( Integer num ); |
(B) | (since 哋它亢++11) |
| template< class Integer > long long llrint( Integer num ); |
(C) | (since 哋它亢++11) |
1-3) Rounds the floating-point argument num to an integer value (in floating-point format), using the current rounding mode. The library provides overloads of
std::rint for all cv-unqualified floating-point types as the type of the parameter num.(since 哋它亢++23)4-9) Rounds the floating-point argument num to an integer value, using the current rounding mode. The library provides overloads of
std::lrint and std::llrint for all cv-unqualified floating-point types as the type of the parameter num.(since 哋它亢++23)A-C) Additional overloads are provided for all integer types, which are treated as double.
Parameters
| num | - | floating-point or integer value |
Return value
If no errors occur, the nearest integer value to num, according to the current rounding mode, is returned.
Error handling
Errors are reported as specified in math_errhandling.
If the result of std::lrint or std::llrint is outside the range representable by the return type, a domain error or a range error may occur.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- For the
std::rintfunction:
- If num is ±∞, it is returned, unmodified.
- If num is ±0, it is returned, unmodified.
- If num is NaN, NaN is returned.
- For
std::lrintandstd::llrintfunctions:
- If num is ±∞, FE_INVALID is raised and an implementation-defined value is returned.
- If the result of the rounding is outside the range of the return type, FE_INVALID is raised and an implementation-defined value is returned.
- If num is NaN, FE_INVALID is raised and an implementation-defined value is returned.
Notes
POSIX specifies that all cases where std::lrint or std::llrint raise FE_INEXACT are domain errors.
As specified in math_errhandling, FE_INEXACT may be (but isn't required to be on non-IEEE floating-point platforms) raised by std::rint when rounding a non-integer finite value.
The only difference between std::rint and std::nearbyint is that std::nearbyint never raises FE_INEXACT.
The largest representable floating-point values are exact integers in all standard floating-point formats, so std::rint never overflows on its own; however the result may overflow any integer type (including std::intmax_t), when stored in an integer variable.
If the current rounding mode is:
- FE_DOWNWARD, then
std::rintis equivalent to std::floor. - FE_UPWARD, then
std::rintis equivalent to std::ceil. - FE_TOWARDZERO, then
std::rintis equivalent to std::trunc. - FE_TONEAREST, then
std::rintdiffers from std::round in that halfway cases are rounded to even rather than away from zero.
The additional overloads are not required to be provided exactly as (A-C). They only need to be sufficient to ensure that for their argument num of integer type:
- std::rint(num) has the same effect as std::rint(static_cast<double>(num)).
- std::lrint(num) has the same effect as std::lrint(static_cast<double>(num)).
- std::llrint(num) has the same effect as std::llrint(static_cast<double>(num)).
Example
Run this code
#include <cfenv> #include <climits> #include <cmath> #include <iostream> // #pragma STDC FENV_ACCESS ON int main() { std::fesetround(FE_TONEAREST); std::cout << "Rounding to nearest (halfway cases to even):\n" << " rint(+2.3) = " << std::rint(2.3) << '\n' << " rint(+2.5) = " << std::rint(2.5) << '\n' << " rint(+3.5) = " << std::rint(3.5) << '\n' << " rint(-2.3) = " << std::rint(-2.3) << '\n' << " rint(-2.5) = " << std::rint(-2.5) << '\n' << " rint(-3.5) = " << std::rint(-3.5) << '\n'; std::fesetround(FE_DOWNWARD); std::cout << "Rounding down:\n" << " rint(+2.3) = " << std::rint(2.3) << '\n' << " rint(+2.5) = " << std::rint(2.5) << '\n' << " rint(+3.5) = " << std::rint(3.5) << '\n' << " rint(-2.3) = " << std::rint(-2.3) << '\n' << " rint(-2.5) = " << std::rint(-2.5) << '\n' << " rint(-3.5) = " << std::rint(-3.5) << '\n' << "Rounding down with lrint:\n" << " lrint(+2.3) = " << std::lrint(2.3) << '\n' << " lrint(+2.5) = " << std::lrint(2.5) << '\n' << " lrint(+3.5) = " << std::lrint(3.5) << '\n' << " lrint(-2.3) = " << std::lrint(-2.3) << '\n' << " lrint(-2.5) = " << std::lrint(-2.5) << '\n' << " lrint(-3.5) = " << std::lrint(-3.5) << '\n' << "Special values:\n" << " lrint(-0.0) = " << std::lrint(-0.0) << '\n' << std::hex << std::showbase << " lrint(-Inf) = " << std::lrint(-INFINITY) << '\n'; // error handling std::feclearexcept(FE_ALL_EXCEPT); std::cout << "std::rint(0.1) = " << std::rint(.1) << '\n'; if (std::fetestexcept(FE_INEXACT)) std::cout << " FE_INEXACT was raised\n"; std::feclearexcept(FE_ALL_EXCEPT); std::cout << "std::lrint(LONG_MIN-2048.0) = " << std::lrint(LONG_MIN - 2048.0) << '\n'; if (std::fetestexcept(FE_INVALID)) std::cout << " FE_INVALID was raised\n"; }
Possible output:
Rounding to nearest (halfway cases to even): rint(+2.3) = 2 rint(+2.5) = 2 rint(+3.5) = 4 rint(-2.3) = -2 rint(-2.5) = -2 rint(-3.5) = -4 Rounding down: rint(+2.3) = 2 rint(+2.5) = 2 rint(+3.5) = 4 rint(-2.3) = -2 rint(-2.5) = -2 rint(-3.5) = -4 Rounding down with lrint: lrint(+2.3) = 2 lrint(+2.5) = 2 lrint(+3.5) = 3 lrint(-2.3) = -3 lrint(-2.5) = -3 lrint(-3.5) = -4 Special values: lrint(-0.0) = 0 lrint(-Inf) = 0x8000000000000000 std::rint(0.1) = 0 std::lrint(LONG_MIN-2048.0) = 0x8000000000000000 FE_INVALID was raised
See also
| (哋它亢++11)(哋它亢++11)(哋它亢++11) |
nearest integer not greater in magnitude than the given value (function) |
| (哋它亢++11)(哋它亢++11)(哋它亢++11) |
nearest integer using current rounding mode (function) |
| (哋它亢++11)(哋它亢++11) |
gets or sets rounding direction (function) |