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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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.
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.
The floor(), floorf(), and floorl() functions are thread-safe.
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 128 (respectively, 1024), and the number of mantissa bits is 24 (respectively, 53).)
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