The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> ceil, ceilf, ceill - ceiling value function

#### SYNOPSIS

> ``#include <math.h>
> double ceil(double` x`);
> float ceilf(float` x`);
> long double ceill(long double` x`);
> ``

#### DESCRIPTION

> [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard.

> 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.

> [MX] If x is NaN, a NaN shall be returned.

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

> [XSI] 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
>   [XSI] 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

> None.

#### 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

> None.

#### FUTURE DIRECTIONS

> None.

#### 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>

#### CHANGE HISTORY

> First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 5

> The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

#### Issue 6

> The ceilf() and ceill() functions are added for alignment with the ISO/IEC 9899:1999 standard.

> The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

> IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

End of informative text.

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