std::ceil,std::ceilf,std::ceill (3) Linux Manual Page

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

Synopsis

Defined in header <cmath>
float ceil ( float arg );
float ceilf( float arg ); (since C++11)
double ceil ( double arg ); (1) (2)
long double ceil ( long double arg );
long double ceill( long double arg ); (3) (since C++11)
double ceil ( IntegralType arg ); (4) (since C++11)
1-3) Computes the smallest integer value not less than arg.
4) A set of overloads or a function template accepting an argument of any integral_type. Equivalent to 2) (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
floorl nearest integer not greater than the given value
           (function)
(C++11)
(C++11)
trunc
truncf
truncl nearest integer not greater in magnitude than the given value
           (function)
(C++11)
(C++11)
(C++11)
round
roundf
roundl
lround
lroundf
lroundl
llround
llroundf
llroundl nearest integer, rounding away from zero in halfway cases
           (function)
(C++11)
(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
           (function)
(C++11)
(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
           (function)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)