# ceil (3p) - Linux Manuals

## ceil: ceiling value function

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.## NAME

ceil, ceilf, ceill - ceiling value function

## SYNOPSIS

**#include <math.h>
**

**
double ceil(double** *x***);
float ceilf(float**

*x*

**);**

long double ceill(long double

long double ceill(long double

*x*

**);**

## DESCRIPTION

These functions shall compute the smallest integral value not less
than *x*.

An application wishing to check for error situations should set *errno*
to zero and call
*feclearexcept*(FE_ALL_EXCEPT) before calling these functions.
On return, if *errno* is non-zero or
*fetestexcept*(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.

## RETURN VALUE

Upon successful completion, *ceil*(), *ceilf*(), and *ceill*()
shall return the smallest integral value not less
than *x*, expressed as a type **double**, **float**, or **long
double**, respectively.

If
*x* is NaN, a NaN shall be returned.

If *x* is ±0 or ±Inf, *x* shall be returned.

If the correct value would cause overflow, a range error shall occur
and *ceil*(), *ceilf*(), and *ceill*() shall
return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.

## ERRORS

These functions shall fail if:

- Range Error
- The result overflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the overflow floating-point exception shall be raised.

*The following sections are informative.*

## EXAMPLES

## APPLICATION USAGE

The integral value returned by these functions need not be expressible
as an **int** or **long**. The return value should
be tested before assigning it to an integer type to avoid the undefined
results of an integer overflow.

The *ceil*() function can only overflow when the floating-point
representation has DBL_MANT_DIG > DBL_MAX_EXP.

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

## RATIONALE

## FUTURE DIRECTIONS

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

## SEE ALSO

*feclearexcept*(), *fetestexcept*(), *floor*(), *isnan*(),
the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, *<math.h>*