ceil, ceilf, ceill - ceiling function: smallest integral value not less than
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)):
_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
For example, ceil(0.5) is 1.0, and ceil(-0.5) is
These functions return the ceiling of x.
If x is integral, +0, -0, NaN, or infinite, x itself
No errors occur. POSIX.1-2001 documents a range error for overflows, but see
For an explanation of the terms used in this section, see attributes(7).
C99, POSIX.1-2001, POSIX.1-2008.
|ceil (), ceilf (), ceill ()
The variant returning double also conforms to SVr4, 4.3BSD,
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
This page is part of release 5.02 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the latest
version of this page, can be found at https://www.kernel.org/doc/man-pages/.