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std::ceil

From cppreference.com
< cpp‎ | numeric‎ | math
 
 
 
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ceil
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Defined in header <cmath>
float       ceil( float arg );
(1)
double      ceil( double arg );
(2)
long double ceil( long double arg );
(3)
double      ceil( Integral 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).

Contents

[edit] Parameters

arg - floating point value

[edit] 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

[edit] 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

[edit] 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;
}

[edit] 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';
}

Output:

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

[edit] See also

nearest integer not greater than the given value
(function) [edit]
(C++11)
nearest integer not greater in magnitude than the given value
(function) [edit]
(C++11)(C++11)(C++11)
nearest integer, rounding away from zero in halfway cases
(function) [edit]
(C++11)
nearest integer using current rounding mode
(function) [edit]
(C++11)(C++11)(C++11)
nearest integer using current rounding mode with
exception if the result differs
(function) [edit]