trunc

 

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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)
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exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
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sqrt cbrt (C99)	hypot (C99) pow
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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)
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ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
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fpclassify (C99)
isfinite (C99)
isinf (C99)
isnan (C99)
isnormal (C99)
signbit (C99)
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HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       truncf( float arg );		(since C99)
double      trunc( double arg );		(since C99)
long double truncl( long double arg );		(since C99)

Computes nearest integer not greater in magnitude than arg.

Parameters

arg

-

floating point value

Return value

Nearest integer not greater in magnitude than arg.

Notes

The integer value can be always represented by the given floating point type.

Example

Run this code

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.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("trunc(+2.4)      = %+.1f\n", trunc(+2.4));
    printf("trunc(-2.4)      = %+.1f\n", trunc(-2.4));
    printf("trunc(+0.0)      = %+.1f\n", trunc(+0.0));
    printf("trunc(-0.0)      = %+.1f\n", trunc(-0.0));
    printf("trunc(+INFINITY) = %+f\n",   trunc(+INFINITY));
    printf("trunc(-INFINITY) = %+f\n",   trunc(-INFINITY));
    printf("trunc(NAN)       = %f\n",    trunc(NAN));
    printf("\n");
 
    /* no "inexact" floating-point exception for finite non-integer arguments */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("trunc(2.4)       = %.1f\n", trunc(2.4));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
 
    return 0;
}

Possible output:

trunc(+2.4)      = +2.0
trunc(-2.4)      = -2.0
trunc(+0.0)      = +0.0
trunc(-0.0)      = -0.0
trunc(+INFINITY) = +inf
trunc(-INFINITY) = -inf
trunc(NAN)       = nan
 
trunc(2.4)       = 2.0
Success
current exceptions raised:  none

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)
roundlroundllround (C99)(C99)(C99)	rounds to nearest integer, rounding away from zero in halfway cases (function)
C++ documentation for trunc