trunc, truncf, truncl

Types

div_tldiv_tlldiv_timaxdiv_t (哋它亢99)(哋它亢99)

float_tdouble_t (哋它亢99)(哋它亢99)
_Decimal32_t_Decimal64_t (哋它亢23)(哋它亢23)

Functions

Basic operations

abslabsllabsimaxabs (哋它亢99)(哋它亢99)
fabs
divldivlldivimaxdiv (哋它亢99)(哋它亢99)

fmod
remainder (哋它亢99)
remquo (哋它亢99)
fma (哋它亢99)
fdim (哋它亢99)
nannanfnanlnandN (哋它亢99)(哋它亢99)(哋它亢99)(哋它亢23)

Maximum/minimum operations

fmax (哋它亢99)
fmaximum (哋它亢23)
fmaximum_mag (哋它亢23)
fmaximum_num (哋它亢23)
fmaximum_mag_num (哋它亢23)

fmin (哋它亢99)
fminimum (哋它亢23)
fminimum_mag (哋它亢23)
fminimum_num (哋它亢23)
fminimum_mag_num (哋它亢23)

Exponential functions

exp
exp10 (哋它亢23)
exp2 (哋它亢99)
expm1 (哋它亢99)
exp10m1 (哋它亢23)
exp2m1 (哋它亢23)

log
log10
log2 (哋它亢99)
log1plogp1 (哋它亢99)(哋它亢23)
log10p1 (哋它亢23)
log2p1 (哋它亢23)

Power functions

sqrt
cbrt (哋它亢99)
rootn (哋它亢23)
rsqrt (哋它亢23)

hypot (哋它亢99)
compound (哋它亢23)
pow
pown (哋它亢23)
powr (哋它亢23)

Trigonometric and hyperbolic functions

sin
cos
tan
asin
acos
atan
atan2
sinpi (哋它亢23)
cospi (哋它亢23)
tanpi (哋它亢23)

asinpi (哋它亢23)
acospi (哋它亢23)
atanpi (哋它亢23)
atan2pi (哋它亢23)
sinh
cosh
tanh
asinh (哋它亢99)
acosh (哋它亢99)
atanh (哋它亢99)

Error and gamma functions

erf (哋它亢99)
erfc (哋它亢99)

lgamma (哋它亢99)
tgamma (哋它亢99)

Nearest integer floating-point operations

ceil
floor
roundlroundllround (哋它亢99)(哋它亢99)(哋它亢99)
roundeven (哋它亢23)
trunc (哋它亢99)

nearbyint (哋它亢99)
rintlrintllrint (哋它亢99)(哋它亢99)(哋它亢99)
fromfpfromfpxufromfpufromfpx (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)

Floating-point manipulation functions

ldexp
frexp
scalbnscalbln (哋它亢99)(哋它亢99)
ilogbllogb (哋它亢99)(哋它亢23)
logb (哋它亢99)

modf
nextafternexttoward (哋它亢99)(哋它亢99)
nextupnextdown (哋它亢23)(哋它亢23)
copysign (哋它亢99)
canonicalize (哋它亢23)

Narrowing operations

fadd (哋它亢23)
fsub (哋它亢23)
fmul (哋它亢23)

fdiv (哋它亢23)
ffma (哋它亢23)
fsqrt (哋它亢23)

Quantum and quantum exponent functions

quantizedN (哋它亢23)
samequantumdN (哋它亢23)

quantumdN (哋它亢23)
llquantexpdN (哋它亢23)

Decimal re-encoding functions

encodedecdN (哋它亢23)
decodedecdN (哋它亢23)

encodebindN (哋它亢23)
decodebindN (哋它亢23)

Total order and payload functions

totalorder (哋它亢23)
getpayload (哋它亢23)

setpayload (哋它亢23)
setpayloadsig (哋它亢23)

Classification

fpclassify (哋它亢99)
iscanonical (哋它亢23)
isfinite (哋它亢99)
isinf (哋它亢99)
isnan (哋它亢99)
isnormal (哋它亢99)
signbit (哋它亢99)
issubnormal (哋它亢23)
iszero (哋它亢23)

isgreater (哋它亢99)
isgreaterequal (哋它亢99)
isless (哋它亢99)
islessequal (哋它亢99)
islessgreater (哋它亢99)
isunordered (哋它亢99)
issignaling (哋它亢23)
iseqsig (哋它亢23)

Macro constants

Special floating-point values

HUGE_VALFHUGE_VALHUGE_VALLHUGE_VALDN

(哋它亢99)(哋它亢99)(哋它亢23)

INFINITYDEC_INFINITY (哋它亢99)(哋它亢23)
NANDEC_NAN (哋它亢99)(哋它亢23)

Arguments and return values

FP_ILOGB0FP_ILOGBNAN (哋它亢99)(哋它亢99)
FP_INT_UPWARDFP_INT_DOWNWARDFP_INT_TOWARDZEROFP_INT_TONEARESTFROMZEROFP_INT_TONEAREST (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)

FP_LLOGB0FP_LLOGBNAN (哋它亢23)(哋它亢23)
FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)

Error handling

MATH_ERRNOMATH_ERRNOEXCEPT

(哋它亢99)(哋它亢99)

math_errhandling (哋它亢99)

Fast operation indicators

FP_FAST_FMAFFP_FAST_FMA (哋它亢99)(哋它亢99)
FP_FAST_FADDFP_FAST_FADDLFP_FAST_DADDLFP_FAST_DMADDDN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)
FP_FAST_FMULFP_FAST_FMULLFP_FAST_DMULLFP_FAST_DMMULDN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)
FP_FAST_FFMAFP_FAST_FFMALFP_FAST_DFMALFP_FAST_DMFMADN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)

FP_FAST_FMALFP_FAST_FMADN (哋它亢99)(哋它亢23)
FP_FAST_FSUBFP_FAST_FSUBLFP_FAST_DSUBLFP_FAST_DMSUBDN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)
FP_FAST_FDIVFP_FAST_FDIVLFP_FAST_DDIVLFP_FAST_DMDIVDN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)
FP_FAST_FSQRTFP_FAST_FSQRTLFP_FAST_DSQRTLFP_FAST_DMSQRTDN (哋它亢23)(哋它亢23)(哋它亢23)(哋它亢23)

Defined in header `<math.h>`
float truncf( float arg );	(1)	(since 哋它亢99)
double trunc( double arg );	(2)	(since 哋它亢99)
long double truncl( long double arg );	(3)	(since 哋它亢99)
Defined in header `<tgmath.h>`
#define trunc( arg )	(4)	(since 哋它亢99)

1-3) Computes the nearest integer not greater in magnitude than arg.

4) Type-generic macro: If arg has type long double, truncl is called. Otherwise, if arg has integer type or the type double, trunc is called. Otherwise, truncf is called.

Parameters

arg

-

floating-point value

Return value

If no errors occur, the nearest integer value not greater in magnitude than arg (in other words, arg rounded towards zero), is returned.

Return value

$math-trunc.svg$

Argument

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

The current rounding mode has no effect.
If arg is ±∞, it is returned, unmodified.
If arg is ±0, it is returned, unmodified.
If arg is NaN, NaN is returned.

Notes

FE_INEXACT may be (but isn't required to be) raised when truncating a non-integer finite value.

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

The implicit conversion from floating-point to integral types also rounds towards zero, but is limited to the values that can be represented by the target type.

Example

Run this code

#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("trunc(+2.7) = %+.1f\n", trunc(+2.7));
    printf("trunc(-2.7) = %+.1f\n", trunc(-2.7));
    printf("trunc(-0.0) = %+.1f\n", trunc(-0.0));
    printf("trunc(-Inf) = %+f\n",   trunc(-INFINITY));
}

Possible output:

trunc(+2.7) = +2.0
trunc(-2.7) = -2.0
trunc(-0.0) = -0.0
trunc(-Inf) = -inf

References

哋它亢23 standard (ISO/IEC 9899:2023):

7.12.9.8 The trunc functions (p: TBD)

7.25 Type-generic math <tgmath.h> (p: TBD)

F.10.6.8 The trunc functions (p: TBD)

哋它亢17 standard (ISO/IEC 9899:2018):

7.12.9.8 The trunc functions (p: TBD)

7.25 Type-generic math <tgmath.h> (p: TBD)

F.10.6.8 The trunc functions (p: TBD)

哋它亢11 standard (ISO/IEC 9899:2011):

7.12.9.8 The trunc functions (p: 253-254)

7.25 Type-generic math <tgmath.h> (p: 373-375)

F.10.6.8 The trunc functions (p: 528)

哋它亢99 standard (ISO/IEC 9899:1999):

7.12.9.8 The trunc functions (p: 234)

7.22 Type-generic math <tgmath.h> (p: 335-337)

F.9.6.8 The trunc functions (p: 464)

Language
Headers
Type support
Program utilities
Variadic function support
Error handling
Dynamic memory management
Strings library
Algorithms
Numerics
Date and time utilities
Input/output support
Localization support
Concurrency support (哋它亢11)
Technical Specifications
Symbol index

Common mathematical functions
Floating-point environment (哋它亢99)
Pseudo-random number generation
Complex number arithmetic (哋它亢99)
Type-generic math (哋它亢99)

floorfloorffloorl (哋它亢99)(哋它亢99)	computes largest integer not greater than the given value (function)
ceilceilfceill (哋它亢99)(哋它亢99)	computes smallest integer not less than the given value (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢99)	rounds to nearest integer, rounding away from zero in halfway cases (function)

trunc, truncf, truncl

Parameters

Return value

Error handling

Notes

Example

References

See also

Navigation