CEIL
Section: Linux Programmer's Manual (3)
Updated: 20170915
Page Index
NAME
ceil, ceilf, ceill  ceiling function: smallest integral value not
less than argument
SYNOPSIS
#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
DESCRIPTION
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.
RETURN VALUE
These functions return the ceiling of
x.
If
x
is integral, +0, 0, NaN, or infinite,
x
itself is returned.
ERRORS
No errors occur.
POSIX.12001 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

ceil(),
ceilf(),
ceill()
 Thread safety  MTSafe

CONFORMING TO
C99, POSIX.12001, POSIX.12008.
The variant returning
double
also conforms to
SVr4, 4.3BSD, C89.
NOTES
SUSv2 and POSIX.12001 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 errorhandling 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 IEEE754 standard 32bit and 64bit floatingpoint 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.
SEE ALSO
floor(3),
lrint(3),
nearbyint(3),
rint(3),
round(3),
trunc(3)
COLOPHON
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manpages
project.
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https://www.kernel.org/doc/manpages/.