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

 

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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

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

floorfloorffloorl (C++11)(C++11)	nearest integer not greater than the given value (function)
trunctruncftruncl (C++11)(C++11)(C++11)	nearest integer not greater in magnitude than the given value (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)	nearest integer, rounding away from zero in halfway cases (function)
nearbyintnearbyintfnearbyintl (C++11)(C++11)(C++11)	nearest integer using current rounding mode (function)
rintrintfrintllrintlrintflrintlllrintllrintfllrintl (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)	nearest integer using current rounding mode with exception if the result differs (function)
C documentation for ceil