NAME

floor - calculate the floor of a number

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

LIBRARY

Math library (libm, -lm)

SYNOPSIS

Header File

#include <math.h>

Prototype

double floor(double x);

#include <math.h>
double floor(double x);
float floorf(float x);
long double floorl(long double x);

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

floorf(), floorl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

This function returns the floor of x.

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

This function returns, as a double, the largest integer that is not greater than x. You may safely cast that value to a long (or an int if it fits).

These functions return the floor of x.

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

EXAMPLE

#include <math.h>
#include <stdio.h>

int main(void)
{
    printf("This is CS%i\n", (int) floor(50.1));
}

ERRORS

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

ATTRIBUTES

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

Interface	Attribute	Value
floor(), floorf(), floorl()	Thread safety	MT-Safe

STANDARDS

C11, POSIX.1-2008.

HISTORY

C99, POSIX.1-2001.

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 127 (respectively, 1023), and the number of mantissa bits including the implicit bit is 24 (respectively, 53).)