trunc, truncf, truncl

 

C

Language

headers

Type support

Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

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)	isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (C99)
Types
div_tldiv_tlldiv_timaxdiv_t (C99)(C99)	float_tdouble_t (C99)(C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99) FP_FAST_FMAFFP_FAST_FMAFP_FAST_FMAL (C99)(C99)(C99) math_errhandlingMATH_ERRNOMATH_ERRNOEXCEPT (C99)(C99)(C99)	INFINITY (C99) NAN (C99) FP_ILOGB0FP_ILOGBNAN (C99)(C99) FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       truncf( float arg );	(1)	(since C99)
double      trunc( double arg );	(2)	(since C99)
long double truncl( long double arg );	(3)	(since C99)
Defined in header <tgmath.h>
#define trunc( arg )	(4)	(since C99)

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

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

• C11 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)

• C99 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)

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