# CEIL

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

NOTES

SEE ALSO

COLOPHON

## 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.1-2001 documents a range error for overflows,
but see NOTES.

## ATTRIBUTES

For an
explanation of the terms used in this section, see
**attributes**(7).

## CONFORMING TO

C99,
POSIX.1-2001, POSIX.1-2008.

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

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