trunc

trunc, truncf, truncl

float       truncf( float arg );

double      trunc( double arg );

long double truncl( long double arg );

#define trunc( arg )

Parameters

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

#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));
}

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