floor man page

floor, floorf, floorl — largest integral value not greater than argument


#include <math.h>

double floor(double x);

float floorf(float x);

long double floorl(long double x);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

floorf(), floorl():

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


These functions return the largest integral value that is not greater than x.

For example, floor(0.5) is 0.0, and floor(-0.5) is -1.0.

Return Value

These functions return the floor of x.

If x is integral, +0, -0, NaN, or an infinity, x itself is returned.


No errors occur. POSIX.1-2001 documents a range error for overflows, but see Notes.


For an explanation of the terms used in this section, see attributes(7).

floor(), floorf(), floorl()Thread safetyMT-Safe

Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD, C89.


SUSv2 and POSIX.1-2001 contain text about overflow (which might set errno to ERANGE, or raise an FE_OVERFLOW exception). In practice, the result cannot overflow on any current machine, so this error-handling stuff is just nonsense. (More precisely, overflow can happen only when the maximum value of the exponent is smaller than the number of mantissa bits. For the IEEE-754 standard 32-bit and 64-bit floating-point numbers the maximum value of the exponent is 128 (respectively, 1024), and the number of mantissa bits is 24 (respectively, 53).)

See Also

ceil(3), lrint(3), nearbyint(3), rint(3), round(3), trunc(3)

Referenced By

abs(3), ceil(3), fabs(3), lrint(3), lround(3), rint(3), round(3), trunc(3).

Explore man page connections for floor(3).

floorf(3) and floorl(3) are aliases of floor(3).