NAME

trunc, truncf, truncl — round to truncated integer value

SYNOPSIS

#include <math.h>

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


DESCRIPTION

^[CX] 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.1-2024 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.

^[MX] These functions may raise the inexact floating-point exception for finite non-integer arguments.

RETURN VALUE

Upon successful completion, these functions shall return the truncated integer value.
^[MX] The returned value shall be exact, shall be independent of the current rounding direction mode, and shall have the same sign as x.

^[MX] If x is NaN, a NaN shall be returned.

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

ERRORS

No errors are defined.

EXAMPLES

None.

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.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

XBD <math.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0684 [346] is applied.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.