**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**(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; or __cc__ __-std=c99__

**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.

**CONFORMING** **TO**

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
__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.

**SEE ALSO**

**floor**(3), **lrint**(3), **nearbyint**(3), **rint**(3), **round**(3), **trunc**(3)

**COLOPHON**

This page is part of release 3.24 of the Linux __man-pages__ project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2008-08-05