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)