ceil, ceilf, ceill - ceiling function: smallest integral value not less than argument

Math library (`libm`

, `-lm`

)

```
#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)):

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 |

Thread safety | MT-Safe |

C11, POSIX.1-2008.

C99, POSIX.1-2001.

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 127 (respectively, 1023), and the
number of mantissa bits including the implicit bit 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.