ceil - Man Page

ceiling value function


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.


#include <math.h>

double ceil(double x);
float ceilf(float x);
long double ceill(long double x);


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 POSIX.1-2017 defers to the ISO C standard.

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

Return Value

The result shall have the same sign as x.

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.


No errors are defined.

The following sections are informative.



Application Usage

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

These functions may raise the inexact floating-point exception if the result differs in value from the argument.



Future Directions


See Also

feclearexcept(), fetestexcept(), floor(), isnan()

The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>

Referenced By

floor(3p), math.h(0p), rint(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual