std::rint, std::rintf, std::rintl, std::lrint, std::lrintf, std::lrintl, std::llrint, std::llrintf

 

C++

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Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

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Filesystem library (C++17)

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Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Numerics library

Common mathematical functions

Mathematical special functions (C++17)

Mathematical constants (C++20)

Floating-point environment (C++11)

Complex numbers

Numeric arrays

Pseudo-random number generation

Factor operations

gcd (C++17)

lcm (C++17)

Interpolations

midpoint (C++20)

lerp (C++20)

Generic numeric operations

iota (C++11)

ranges::iota (C++23)

accumulate

inner_product

adjacent_difference

partial_sum

reduce (C++17)

transform_reduce (C++17)

inclusive_scan (C++17)

exclusive_scan (C++17)

transform_inclusive_scan (C++17)

transform_exclusive_scan (C++17)

Bit operations

bit_cast (C++20)

byteswap (C++23)

has_single_bit (C++20)

bit_ceil (C++20)

bit_floor (C++20)

bit_width (C++20)

rotl (C++20)

rotr (C++20)

countl_zero (C++20)

countl_one (C++20)

countr_zero (C++20)

countr_one (C++20)

popcount (C++20)

endian (C++20)

 

Common mathematical functions

Functions
Basic operations
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
Exponential functions
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
Power functions
sqrt cbrt (C++11)	hypot (C++11) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Error and gamma functions
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Nearest integer floating point operations
ceil floor roundlroundllround (C++11)(C++11)(C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11)(C++11)(C++11)
Floating point manipulation functions
ldexp scalbnscalbln (C++11)(C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11)(C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

Defined in header <cmath>
Rounding to floating-point types
	(1)
float       rint ( float num ); double      rint ( double num ); long double rint ( long double num );			(since C++11) (until C++23)
/* floating-point-type */ rint( /* floating-point-type */ num );			(since C++23)
float       rintf( float num );		(2)	(since C++11)
long double rintl( long double num );		(3)	(since C++11)
Rounding to long
		(4)
long lrint ( float num ); long lrint ( double num ); long lrint ( long double num );				(since C++11) (until C++23)
long lrint ( /* floating-point-type */ num );				(since C++23)
long lrintf( float num );			(5)	(since C++11)
long lrintl( long double num );			(6)	(since C++11)
Rounding to long long
			(7)
long long llrint ( float num ); long long llrint ( double num ); long long llrint ( long double num );					(since C++11) (until C++23)
long long llrint ( /* floating-point-type */ num );					(since C++23)
long long llrintf( float num );				(8)	(since C++11)
long long llrintl( long double num );				(9)	(since C++11)
Additional overloads
Defined in header <cmath>
template< class Integer > double rint( Integer num );				(A)	(since C++11)
template< class Integer > long lrint( Integer num );				(B)	(since C++11)
template< class Integer > long long llrint( Integer num );				(C)	(since C++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 C++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 C++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::rint function:

• If num is ±∞, it is returned, unmodified
• If num is ±0, it is returned, unmodified
• If num is NaN, NaN is returned

For std::lrint and std::llrint functions:

• 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::rint is equivalent to std::floor.
• FE_UPWARD, then std::rint is equivalent to std::ceil.
• FE_TOWARDZERO, then std::rint is equivalent to std::trunc
• FE_TONEAREST, then std::rint differs 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

trunctruncftruncl (C++11)(C++11)(C++11)	nearest integer not greater in magnitude than the given value (function)
nearbyintnearbyintfnearbyintl (C++11)(C++11)(C++11)	nearest integer using current rounding mode (function)
fegetroundfesetround (C++11)(C++11)	gets or sets rounding direction (function)