The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The IEEE and The Open Group

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] [Option Start] 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. [Option End]

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

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

RETURN VALUE

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

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

If x is ±0 or ±Inf, x shall be returned. [Option End]

ERRORS

No errors are defined.


The following sections are informative.

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.

End of informative text.

 

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