std::ceil, std::ceilf, std::ceill
<cmath>
double ceil ( double num );
ceil ( /*floating-point-type*/ num );
(constexpr since C++23)
(constexpr since C++23)
<simd>
constexpr /*deduced-simd-t*/<V>
<cmath>
double ceil ( Integer num );
std::ceil for all cv-unqualified floating-point types as the type of the parameter.(since C++23)std::ceil on v_num.- (See math-floating-point and deduced-simd-t for their definitions.)
[edit] Parameters
[edit] Return value
If no errors occur, the smallest integer value not less than num, that is ⌈num⌉, is returned.
[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 num is ±∞, it is returned unmodified.
- If num is ±0, it is returned, unmodified.
- If num is NaN, NaN is returned.
[edit] 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:
#include <cfenv> #include <cmath> #pragma STDC FENV_ACCESS ON double ceil(double x) { int save_round = std::fegetround (); std::fesetround (FE_UPWARD ); double result = std::rint (x); // or std::nearbyint std::fesetround (save_round); return result; }
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<double>(num)).
[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
(function) [edit]
(function) [edit]
exception if the result differs
(function) [edit]