trunc - Man Page

round to truncated integer value


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <math.h>

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


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

These functions shall round their argument to the integer value, in floating format, nearest to but no larger in magnitude than the argument.

Return Value

Upon successful completion, these functions shall return the truncated integer value.
The result shall have the same sign as x.

If x is NaN, a NaN shall be returned.

If x is ±0 or ±Inf, x shall be returned.


No errors are defined.

The following sections are informative.



Application Usage

The integral value returned by these functions need not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.

These functions may raise the inexact floating-point exception if the result differs in value from the argument.



Future Directions


See Also

The Base Definitions volume of POSIX.1-2017, <math.h>

Referenced By


2017 IEEE/The Open Group POSIX Programmer's Manual