ceil, ceilf, ceill - ceiling function: smallest integral value not less than
argument
#include <math.h>
double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
Link with
-lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ceilf(),
ceill():
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
These functions return the smallest integral value that is not less than
x.
For example,
ceil(0.5) is 1.0, and
ceil(-0.5) is 0.0.
These functions return the ceiling of
x.
If
x is integral, +0, -0, NaN, or infinite,
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).
| Interface |
Attribute |
Value |
| ceil (), ceilf (), ceill () |
Thread safety |
MT-Safe |
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).)
The integral value returned by these functions may be too large to store in an
integer type (
int,
long, etc.). To avoid an overflow, which will
produce undefined results, an application should perform a range check on the
returned value before assigning it to an integer type.
floor(3),
lrint(3),
nearbyint(3),
rint(3),
round(3),
trunc(3)