Section (3) ceil
ceil, ceilf, ceill — ceiling function: smallest integral value not less than argument
||long double x
These functions return the smallest integral value that is
not less than
ceil(0.5) is 1.0, and
These functions return the ceiling of
x is integral,
+0, −0, NaN, or infinite,
x itself is returned.
For an explanation of the terms used in this section, see attributes(7).
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
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,
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.
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Copyright 2001 Andries Brouwer <aebcwi.nl>.
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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