std::ceil,std::ceilf,std::ceill (3) - Linux Manuals

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

NAME

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

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