round, roundf, roundl, lround, lroundf, lroundl, llround, llroundf, llroundl
From cppreference.com
Common mathematical functions
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Defined in header <math.h> | ||
float roundf(float arg); | (1) | (since C99) |
double round(double arg); | (2) | (since C99) |
longdouble roundl(longdouble arg); | (3) | (since C99) |
Defined in header <tgmath.h> | ||
#define round( arg ) | (4) | (since C99) |
Defined in header <math.h> | ||
long lroundf(float arg); | (5) | (since C99) |
long lround(double arg); | (6) | (since C99) |
long lroundl(longdouble arg); | (7) | (since C99) |
Defined in header <tgmath.h> | ||
#define lround( arg ) | (8) | (since C99) |
Defined in header <math.h> | ||
longlong llroundf(float arg); | (9) | (since C99) |
longlong llround(double arg); | (10) | (since C99) |
longlong llroundl(longdouble arg); | (11) | (since C99) |
Defined in header <tgmath.h> | ||
#define llround( arg ) | (12) | (since C99) |
1-3) Computes the nearest integer value toarg (in floating-point format), rounding halfway cases away from zero, regardless of the current rounding mode.
5-7, 9-11) Computes the nearest integer value toarg (in integer format), rounding halfway cases away from zero, regardless of the current rounding mode.
4,8,12) Type-generic macros: Ifarg has typelongdouble,
roundl,lroundl,llroundl is called. Otherwise, ifarg has integer type or the typedouble,round,lround,llround is called. Otherwise,roundf,lroundf,llroundf is called, respectively.Contents |
[edit]Parameters
| arg | - | floating-point value |
[edit]Return value
If no errors occur, the nearest integer value toarg, rounding halfway cases away from zero, is returned.
Return value
Argument
If a domain error occurs, an implementation-defined value is returned.
[edit]Error handling
Errors are reported as specified inmath_errhandling.
If the result oflround orllround 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
round,roundf, androundlfunction:- The currentrounding mode has no effect.
- Ifarg is ±∞, it is returned, unmodified.
- Ifarg is ±0, it is returned, unmodified.
- Ifarg is NaN, NaN is returned.
- For
lroundandllroundfamilies of functions:- FE_INEXACT is never raised.
- The currentrounding mode has no effect.
- Ifarg 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.
- Ifarg is NaN,FE_INVALID is raised and an implementation-defined value is returned.
[edit]Notes
FE_INEXACT may be (but isn't required to be) raised byround when rounding a non-integer finite value.
The largest representable floating-point values are exact integers in all standard floating-point formats, soround never overflows on its own; however the result may overflow any integer type (includingintmax_t), when stored in an integer variable.
POSIX specifies that all cases wherelround orllround raiseFE_INVALID are domain errors.
Thedouble version ofround behaves as if implemented as follows:
[edit]Example
Run this code
#include <assert.h>#include <fenv.h>#include <float.h>#include <limits.h>#include <math.h>#include <stdio.h>// #pragma STDC FENV_ACCESS ON double custom_round(double x){returnsignbit(x)?ceil(x-0.5):floor(x+0.5);} void test_custom_round(){constdouble sample[]={0.0,2.3,2.5-DBL_EPSILON,2.5,2.5+DBL_EPSILON,2.7, INFINITY};for(size_t t=0; t<sizeof sample/sizeof(double);++t)assert(round(+sample[t])== custom_round(+sample[t])&& round(-sample[t])== custom_round(-sample[t]));} int main(void){// roundprintf("round(+2.3) = %+.1f ", round(2.3));printf("round(+2.5) = %+.1f ", round(2.5));printf("round(+2.7) = %+.1f\n", round(2.7));printf("round(-2.3) = %+.1f ", round(-2.3));printf("round(-2.5) = %+.1f ", round(-2.5));printf("round(-2.7) = %+.1f\n", round(-2.7)); printf("round(-0.0) = %+.1f\n", round(-0.0));printf("round(-Inf) = %+f\n", round(-INFINITY)); test_custom_round(); // lroundprintf("lround(+2.3) = %+ld ", lround(2.3));printf("lround(+2.5) = %+ld ", lround(2.5));printf("lround(+2.7) = %+ld\n", lround(2.7));printf("lround(-2.3) = %+ld ", lround(-2.3));printf("lround(-2.5) = %+ld ", lround(-2.5));printf("lround(-2.7) = %+ld\n", lround(-2.7)); printf("lround(-0.0) = %+ld\n", lround(-0.0));printf("lround(-Inf) = %+ld\n", lround(-INFINITY));// FE_INVALID raised // error handlingfeclearexcept(FE_ALL_EXCEPT);printf("lround(LONG_MAX+1.5) = %ld\n", lround(LONG_MAX+1.5));if(fetestexcept(FE_INVALID))puts(" FE_INVALID was raised");}
Possible output:
round(+2.3) = +2.0 round(+2.5) = +3.0 round(+2.7) = +3.0round(-2.3) = -2.0 round(-2.5) = -3.0 round(-2.7) = -3.0round(-0.0) = -0.0round(-Inf) = -inflround(+2.3) = +2 lround(+2.5) = +3 lround(+2.7) = +3lround(-2.3) = -2 lround(-2.5) = -3 lround(-2.7) = -3lround(-0.0) = +0lround(-Inf) = -9223372036854775808lround(LONG_MAX+1.5) = -9223372036854775808 FE_INVALID was raised
[edit]References
- C23 standard (ISO/IEC 9899:2024):
- 7.12.9.6 The round functions (p: TBD)
- 7.12.9.7 The lround and llround functions (p: TBD)
- 7.25 Type-generic math <tgmath.h> (p: TBD)
- F.10.6.6 The round functions (p: TBD)
- F.10.6.7 The lround and llround functions (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
- 7.12.9.6 The round functions (p: 184)
- 7.12.9.7 The lround and llround functions (p: 184-185)
- 7.25 Type-generic math <tgmath.h> (p: 272-273)
- F.10.6.6 The round functions (p: 384)
- F.10.6.7 The lround and llround functions (p: 385)
- C11 standard (ISO/IEC 9899:2011):
- 7.12.9.6 The round functions (p: 253)
- 7.12.9.7 The lround and llround functions (p: 253)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.6.6 The round functions (p: 527)
- F.10.6.7 The lround and llround functions (p: 528)
- C99 standard (ISO/IEC 9899:1999):
- 7.12.9.6 The round functions (p: 233)
- 7.12.9.7 The lround and llround functions (p: 234)
- 7.22 Type-generic math <tgmath.h> (p: 335-337)
- F.9.6.6 The round functions (p: 464)
- F.9.6.7 The lround and llround functions (p: 464)
[edit]See also
(C99)(C99) | computes largest integer not greater than the given value (function)[edit] |
(C99)(C99) | computes smallest integer not less than the given value (function)[edit] |
(C99)(C99)(C99) | rounds to nearest integer not greater in magnitude than the given value (function)[edit] |
C++ documentation forround | |
