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

float       ceil ( float num );
double      ceil ( double num );
long double ceil ( long double num );

constexpr /* floating-point-type */
            ceil ( /* floating-point-type */ num );

float       ceilf( float num );

long double ceill( long double num );

template< class Integer >
double      ceil ( Integer num );

double

Parameters

Return value

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

Return value

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

#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';
}

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

See also

External links