NAME

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

Synopsis

Defined in header <cmath>
float ceil ( float arg ); (1) (constexpr since C++23)
float ceilf( float arg ); (2) (since C++11)
(constexpr since C++23)
double ceil ( double arg ); (3) (constexpr since C++23)
long double ceil ( long double arg ); (4) (constexpr since C++23)
long double ceill( long double arg ); (5) (since C++11)
(constexpr since C++23)
double ceil ( IntegralType arg ); (6) (since C++11)
(constexpr since C++23)

1-5) Computes the smallest integer value not less than arg.
6) A set of overloads or a function template accepting an argument of any integral
type. Equivalent to (3) (the argument is cast to double).

Parameters

arg - floating point value

Return value

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

Return value

math-ceil.svg
Argument

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 arg is ±∞, it is returned unmodified
* If arg is ±0, it is returned, unmodified
* If arg is NaN, NaN is returned

Notes

FE_INEXACT may be (but isn't 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.

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

#include <cmath>
#include <cfenv>
#pragma STDC FENV_ACCESS ON
double ceil(double x)
{
double result;
int save_round = std::fegetround();
std::fesetround(FE_UPWARD);
result = std::rint(x); // or std::nearbyint
std::fesetround(save_round);
return result;
}

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)