NAME¶

std::ceil,std::ceilf,std::ceill - std::ceil,std::ceilf,std::ceill

Synopsis¶

Defined in header <cmath>
float ceil ( float num );

double ceil ( double num ); (until C++23)

long double ceil ( long double num );
constexpr /* floating-point-type */ (since C++23)
ceil ( /* floating-point-type */ num );
float ceilf( float num ); (1) (2) (since C++11)
(constexpr since C++23)
long double ceill( long double num ); (3) (since C++11)
(constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++23)
double ceil ( Integer num );

1-3) Computes the least integer value not less than num.
The library provides overloads of std::ceil for all cv-unqualified floating-point
types as the type of the parameter.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

Parameters¶

num - floating point or integer value

Return value¶

If no errors occur, the smallest integer value not less than num, that is ⌈num⌉, is
returned.

Return value¶

math-ceil.svg
num

Error handling¶

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

* The current rounding mode has no effect.
* If num is ±∞, it is returned unmodified.
* If num is ±0, it is returned, unmodified.
* If num is NaN, NaN is returned.

Notes¶

FE_INEXACT may be (but is not required to be) raised when rounding a non-integer
finite value.

The largest representable floating-point values are exact integers in all standard
floating-point formats, so this function never overflows on its own; however the
result may overflow any integer type (including std::intmax_t), when stored in an
integer variable. It is for this reason that the return type is floating-point not
integral.

This function (for double argument) behaves as if (except for the freedom to not
raise FE_INEXACT) implemented by the following code:

#include <cfenv>
#include <cmath>
#pragma STDC FENV_ACCESS ON

double ceil(double x)
{
int save_round = std::fegetround();
std::fesetround(FE_UPWARD);
double result = std::rint(x); // or std::nearbyint
std::fesetround(save_round);
return result;
}

The additional overloads are not required to be provided exactly as (A). They only
need to be sufficient to ensure that for their argument num of integer type,
std::ceil(num) has the same effect as std::ceil(static_cast<double>(num)).

Example¶

// Run this code

#include <cmath>
#include <iostream>

int main()
{
std::cout << std::fixed
<< "ceil(+2.4) = " << std::ceil(+2.4) << '\n'
<< "ceil(-2.4) = " << std::ceil(-2.4) << '\n'
<< "ceil(-0.0) = " << std::ceil(-0.0) << '\n'
<< "ceil(-Inf) = " << std::ceil(-INFINITY) << '\n';
}

Output:¶

ceil(+2.4) = 3.000000
ceil(-2.4) = -2.000000
ceil(-0.0) = -0.000000
ceil(-Inf) = -inf

See also¶

floor
floorf nearest integer not greater than the given value
floorl (function)
(C++11)
(C++11)
trunc
truncf
truncl nearest integer not greater in magnitude than the given value
(C++11) (function)
(C++11)
(C++11)
round
roundf
roundl
lround
lroundf
lroundl
llround
llroundf
llroundl nearest integer, rounding away from zero in halfway cases
(C++11) (function)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
nearbyint
nearbyintf
nearbyintl nearest integer using current rounding mode
(C++11) (function)
(C++11)
(C++11)
rint
rintf
rintl
lrint
lrintf
lrintl
llrint
llrintf nearest integer using current rounding mode with
llrintl exception if the result differs
(C++11) (function)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
C documentation for
ceil

External links¶

Fast ceiling of an integer division — StackOverflow