ceill(3) — Linux manual page


CEIL(3)                   Linux Programmer's Manual                  CEIL(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       These functions return the ceiling of x.

       If x is integral, +0, -0, NaN, or infinite, x itself is returned.

ERRORS         top

       No errors occur.  POSIX.1-2001 documents a range error for overflows,
       but see NOTES.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                Attribute     Value   │
       │ceil(), ceilf(), ceill() │ Thread safety │ MT-Safe │

CONFORMING TO         top

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

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

NOTES         top

       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

SEE ALSO         top

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

COLOPHON         top

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                                 2017-09-15                          CEIL(3)