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

Since C++23

Header: <cmath>

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)

# Declarations

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

(until C++23)

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

(since C++23)

float ceilf( float num );

(since C++11) (constexpr since C++23)

long double ceill( long double num );

(since C++11) (constexpr since C++23)

SIMD overload (since C++26)

template< /*math-floating-point*/ V >
constexpr /*deduced-simd-t*/<V>
ceil ( const V& v_num );

(since C++26)

Additional overloads (since C++11)

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

(constexpr since C++23)

# 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.

# 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:

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(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';
}