trunc - Man Page

round to integer, toward zero


Math library (libm, -lm)


#include <math.h>

double trunc(double x);
float truncf(float x);
long double truncl(long double x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

trunc(), truncf(), truncl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L


These functions round x to the nearest integer value that is not larger in magnitude than x.

Return Value

These functions return the rounded integer value, in floating format.

If x is integral, infinite, or NaN, x itself is returned.


No errors occur.


For an explanation of the terms used in this section, see attributes(7).

trunc(), truncf(), truncl()Thread safetyMT-Safe


C11, POSIX.1-2008.


glibc 2.1. C99, POSIX.1-2001.


The integral value returned by these functions may be too large to store in an integer type (int, long, etc.). To avoid an overflow, which will produce undefined results, an application should perform a range check on the returned value before assigning it to an integer type.

See Also

ceil(3), floor(3), lrint(3), nearbyint(3), rint(3), round(3)

Referenced By

ceil(3), floor(3), rint(3), round(3).

The man pages truncf(3) and truncl(3) are aliases of trunc(3).

2023-10-31 Linux man-pages 6.06