Legacy Document

trunc

You can use the trunc function to truncate the fractional part of a real number so that just the integer part remains.

double_t trunc (double_t x);

x

Any floating-point number.

DESCRIPTION

The trunc function chops off the fractional part of its argument. This is an ANSI standard C library function.

This function is the same as performing the following code sequence:

r = fegetround();          /* save current rounding direction */
fesetround(FE_TOWARDZERO); /* round toward zero */
rint(x);                   /* round to integer */
fesetround(r);             /* restore rounding direction */

EXCEPTIONS

When x is finite and nonzero, the result of $trunc(x)$ is exact.

SPECIAL CASES

Table 9-7 shows the results when the argument to the trunc function is a zero, a NaN, or an Infinity.

Special cases for the trunc function

Operation	Result	Exceptions raised
$trunc(+0)$	+0	None
$trunc(-0)$	$-0$	None
$trunc(NaN)$	NaN	None[18]
$trunc(+$ )	+	None
$trunc(-$ )	$-$	None

EXAMPLES

z = trunc(+INFINITY);   /* z = +INFINITY because +   is already an 
                           integer value by definition. */
z = trunc(300.1);       /* z = 300.0 */
z = trunc(-300.1);      /* z = -300.0 */

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[18] If the NaN is a signaling NaN, the invalid exception is raised.