floor - Man Page

floor function


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.


#include <math.h>

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.

Return Value

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.


No errors are defined.

The following sections are informative.



Application Usage

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.



Future Directions


See Also

ceil(), feclearexcept(), fetestexcept(), isnan()

Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>

Referenced By

ceil(3p), math.h(0p), rint(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual