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rint

Defined in header <math.h>
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float rintf( float arg );
 (1) (since C99)
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double rint( double arg );
 (2) (since C99)
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long double rintl( long double arg );
 (3) (since C99)
Defined in header <tgmath.h>
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#define rint( arg )
 (4) (since C99)
Defined in header <math.h>
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long lrintf( float arg );
 (5) (since C99)
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long lrint( double arg );
 (6) (since C99)
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long lrintl( long double arg );
 (7) (since C99)
Defined in header <tgmath.h>
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#define lrint( arg )
 (8) (since C99)
Defined in header <math.h>
1
long long llrintf( float arg );
 (9) (since C99)
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long long llrint( double arg );
 (10) (since C99)
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long long llrintl( long double arg );
 (11) (since C99)
Defined in header <tgmath.h>
1
#define llrint( arg )
 (12) (since C99)
1-3) Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.
5-7, 9-11) Rounds the floating-point argument arg to an integer value in integer format, using the current rounding mode.
4,8,12) Type-generic macros: If arg has type long double, rintl, lrintl, llrintl is called. Otherwise, if arg has integer type or the type double, rint, lrint, llrint is called. Otherwise, rintf, lrintf, llrintf is called, respectively.

Parameters

arg - floating point value

Return value

If no errors occur, the nearest integer value to arg, according to the current rounding mode, is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the result of lrint or 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 rint function:

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

For lrint and llrint functions:

  • If arg 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 arg is NaN, FE_INVALID is raised and an implementation-defined value is returned

Notes

POSIX specifies that all cases where lrint or 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 rint when rounding a non-integer finite value.

The only difference between rint and nearbyint is that nearbyint never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so rint never overflows on its own; however the result may overflow any integer type (including intmax_t), when stored in an integer variable.

If the current rounding mode is...

Example

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#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <limits.h>
  
int main(void)
{
#pragma STDC FENV_ACCESS ON
    fesetround(FE_TONEAREST);
    printf("rounding to nearest (halfway cases to even):\n"
           "rint(+2.3) = %+.1f  ", rint(2.3));
    printf("rint(+2.5) = %+.1f  ", rint(2.5));
    printf("rint(+3.5) = %+.1f\n", rint(3.5));
    printf("rint(-2.3) = %+.1f  ", rint(-2.3));
    printf("rint(-2.5) = %+.1f  ", rint(-2.5));
    printf("rint(-3.5) = %+.1f\n", rint(-3.5));
  
    fesetround(FE_DOWNWARD);
    printf("rounding down: \nrint(+2.3) = %+.1f  ", rint(2.3));
    printf("rint(+2.5) = %+.1f  ", rint(2.5));
    printf("rint(+3.5) = %+.1f\n", rint(3.5));
    printf("rint(-2.3) = %+.1f  ", rint(-2.3));
    printf("rint(-2.5) = %+.1f  ", rint(-2.5));
    printf("rint(-3.5) = %+.1f\n", rint(-3.5));
    printf("rounding down with lrint: \nlrint(+2.3) = %ld  ", lrint(2.3));
    printf("lrint(+2.5) = %ld  ", lrint(2.5));
    printf("lrint(+3.5) = %ld\n", lrint(3.5));
    printf("lrint(-2.3) = %ld  ", lrint(-2.3));
    printf("lrint(-2.5) = %ld  ", lrint(-2.5));
    printf("lrint(-3.5) = %ld\n", lrint(-3.5));
  
    printf("lrint(-0.0) = %ld\n", lrint(-0.0));
    printf("lrint(-Inf) = %ld\n", lrint(-INFINITY)); // FE_INVALID raised
  
    // error handling
    feclearexcept(FE_ALL_EXCEPT);
    printf("rint(1.1) = %.1f\n", rint(1.1));
    if(fetestexcept(FE_INEXACT)) puts("    FE_INEXACT was raised");
  
    feclearexcept(FE_ALL_EXCEPT);
    printf("lrint(LONG_MIN-2048.0) = %ld\n", lrint(LONG_MIN-2048.0));
    if(fetestexcept(FE_INVALID)) puts("    FE_INVALID was raised");
}

Possible output:

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rounding to nearest (halfway cases to even):
rint(+2.3) = +2.0  rint(+2.5) = +2.0  rint(+3.5) = +4.0
rint(-2.3) = -2.0  rint(-2.5) = -2.0  rint(-3.5) = -4.0
rounding down:
rint(+2.3) = +2.0  rint(+2.5) = +2.0  rint(+3.5) = +3.0
rint(-2.3) = -3.0  rint(-2.5) = -3.0  rint(-3.5) = -4.0
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
lrint(-0.0) = 0
lrint(-Inf) = -9223372036854775808
rint(1.1) = 1.0
    FE_INEXACT was raised
lrint(LONG_MIN-2048.0) = -9223372036854775808
    FE_INVALID was raised

References

  • C11 standard (ISO/IEC 9899:2011):
    • 7.12.9.4 The rint functions (p: 252)
    • 7.12.9.5 The lrint and llrint functions (p: 252)
    • 7.25 Type-generic math <tgmath.h> (p: 373-375)
    • F.10.6.4 The rint functions (p: 527)
    • F.10.6.5 The lrint and llrint functions (p: 527)
  • C99 standard (ISO/IEC 9899:1999):
    • 7.12.9.4 The rint functions (p: 232-233)
    • 7.12.9.5 The lrint and llrint functions (p: 233)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • F.9.6.4 The rint functions (p: 463)
    • F.9.6.5 The lrint and llrint functions (p: 463)

See also

(C99)(C99)(C99)
 rounds to nearest integer not greater in magnitude than the given value
(function)
(C99)(C99)(C99)
 rounds to an integer using current rounding mode
(function)
(C99)(C99)
 gets or sets rounding direction
(function)
C++ documentation for rint
doc_C_Language
doc_C_Language
2025-01-10 15:47:30
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