round, lround, llround

 

C

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Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abslabsllabsimaxabs (C99) fabs divldivlldivimaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nannanfnanl (C99)(C99)(C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)
Error and gamma functions
erf (C99) erfc (C99)	lgamma (C99) tgamma (C99)
Nearest integer floating point operations
ceil floor roundlroundllround (C99)(C99)(C99)	trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99)
Floating point manipulation functions
ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
Classification
fpclassify (C99)
isfinite (C99)
isinf (C99)
isnan (C99)
isnormal (C99)
signbit (C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       roundf( float arg );		(since C99)
double      round( double arg );		(since C99)
long double roundl( long double arg );		(since C99)
long      lroundf( float arg );		(since C99)
long      lround( double arg );		(since C99)
long      lroundl( long double arg );		(since C99)
long long llroundf( float arg );		(since C99)
long long llround( double arg );		(since C99)
long long llroundl( long double arg );		(since C99)

Computes nearest integer to arg. Number is rounded away from zero in halfway cases

Parameters

arg

-

floating point value

Return value

Nearest integer to arg.

Example

Run this code

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>
#include <limits.h>
#include <string.h>
 
#pragma STDC FENV_ACCESS ON
 
void show_fe_exceptions(void)
{
    printf("current exceptions raised: ");
    if(fetestexcept(FE_DIVBYZERO))     printf(" FE_DIVBYZERO");
    if(fetestexcept(FE_INEXACT))       printf(" FE_INEXACT");
    if(fetestexcept(FE_INVALID))       printf(" FE_INVALID");
    if(fetestexcept(FE_OVERFLOW))      printf(" FE_OVERFLOW");
    if(fetestexcept(FE_UNDERFLOW))     printf(" FE_UNDERFLOW");
    if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none");
    printf("\n");
}
 
int main(void)
{
    printf("round(+2.5)      = %+.1f\n", round(+2.5));   /* rounded away from zero */
    printf("round(-2.5)      = %+.1f\n", round(-2.5));
    printf("round(+1.5)      = %+.1f\n", round(+1.5));
    printf("round(-1.5)      = %+.1f\n", round(-1.5));
    printf("round(+0.0)      = %+.1f\n", round(+0.0));
    printf("round(-0.0)      = %+.1f\n", round(-0.0));
    printf("round(+INFINITY) = %+f\n",   round(+INFINITY));
    printf("round(-INFINITY) = %+f\n",   round(-INFINITY));
    printf("round(NAN)       = %f\n",    round(NAN));
    printf("\n");
 
    /* no "inexact" floating-point exception for finite non-integer arguments */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("round(2.5)       = %.1f\n", round(2.5));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
    printf("\n");
 
    printf("lround(+2.5) = %+ld\n", lround(+2.5));
    printf("lround(-2.5) = %+ld\n", lround(-2.5));
    printf("lround(+1.5) = %+ld\n", lround(+1.5));
    printf("lround(-1.5) = %+ld\n", lround(-1.5));
    printf("\n");
 
    /* rounded value is outside the range of the return type */
    /* neither domain nor range error occurs                 */
    printf("LONG_MAX             = %+ld\n", LONG_MAX);
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("lround(LONG_MAX+1.5) = %+ld\n", lround(LONG_MAX+1.5));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
 
    return 0;
}

Possible output:

round(+2.5)      = +3.0
round(-2.5)      = -3.0
round(+1.5)      = +2.0
round(-1.5)      = -2.0
round(+0.0)      = +0.0
round(-0.0)      = -0.0
round(+INFINITY) = +inf
round(-INFINITY) = -inf
round(NAN)       = nan
 
round(2.5)       = 3.0
Success
current exceptions raised:  none
 
lround(+2.5) = +3
lround(-2.5) = -3
lround(+1.5) = +2
lround(-1.5) = -2
 
LONG_MAX             = +9223372036854775807
lround(LONG_MAX+1.5) = -9223372036854775808
Success
current exceptions raised:  FE_INVALID

See also

floorfloorffloorl (C99)(C99)	computes largest integer not greater than the given value (function)
ceilceilfceill (C99)(C99)	computes smallest integer not less than the given value (function)
trunctruncftruncl (C99)(C99)(C99)	rounds to nearest integer not greater in magnitude than the given value (function)
C++ documentation for round