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.
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 compute the largest integral value not greater
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 returned.
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
These functions may raise the inexact floating-point exception if the
result differs in value from the argument.
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 http://www.unix.org/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
IEEE/The Open Group 2013 FLOOR(3P)