ceil(3) Library Functions Manual ceil(3)
NAME
ceil, ceilf, ceill - ceiling function: smallest integral value not less
than argument
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>
double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
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 <= 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.1-2001 documents a range error for overflows,
but see NOTES.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌───────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────────────────┼───────────────┼─────────┤
│ ceil(), ceilf(), ceill() │ 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.
NOTES
SUSv2 and POSIX.1-2001 contain text about overflow (which might set er-
rno 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 man-
tissa 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 (re-
spectively, 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)
Linux man-pages 6.7 2023-10-31 ceil(3)
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