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.
floor, floorf, floorl — floor function
double floor(double x);
float floorf(float x);
long double floorl(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 compute the largest integral value not
greater than x.
The result shall have the same sign as x.
Upon successful completion, these functions shall return the
largest integral value not greater than x, expressed as a
double, float, or long double, as appropriate for the
return type of the function.
If x is NaN, a NaN shall be returned.
If x is ±0 or ±Inf, x shall be
No errors are defined.
The following sections are informative.
The integral value returned by these functions might 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.
Section 4.20, Treatment of Error Conditions for
Mathematical Functions, <math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .
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