trunc, truncf, truncl — round to integer, toward zero


#include <math.h>

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

Link with -lm.

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

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



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.


These functions first appeared in glibc in version 2.1.


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

Interface Attribute Value
trunc(), truncf(), truncl() Thread safety MT-Safe

Conforming to

C99, POSIX.1-2001, POSIX.1-2008.


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)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

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

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

2019-03-06 Linux Programmer's Manual