Section: POSIX Programmer's Manual (3P)
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.
--- round to truncated integer value
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.1-2008 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
Upon successful completion, these functions shall return the truncated
is NaN, a NaN shall be returned.
is ±0 or ±Inf,
shall be returned.
No errors are defined.
The following sections are informative.
The integral value returned by these functions need not be expressible
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.
The Base Definitions volume of POSIX.1-2008,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see