std::ceil, std::ceilf, std::ceill
Defined in header <cmath> | ||
| (1) | ||
float ceil (float num ); double ceil (double num ); | (until C++23) | |
constexpr/*floating-point-type*/ ceil (/*floating-point-type*/ num ); | (since C++23) | |
float ceilf(float num ); | (2) | (since C++11) (constexpr since C++23) |
longdouble ceill(longdouble num ); | (3) | (since C++11) (constexpr since C++23) |
SIMD overload(since C++26) | ||
Defined in header <simd> | ||
template</*math-floating-point*/ V > constexpr/*deduced-simd-t*/<V> | (S) | (since C++26) |
Additional overloads(since C++11) | ||
Defined in header <cmath> | ||
template<class Integer > double ceil ( Integer num ); | (A) | (constexpr since C++23) |
std::ceil for all cv-unqualified floating-point types as the type of the parameter.(since C++23)S) The SIMD overload performs an element-wise std::ceil on v_num.
| (since C++26) |
A) Additional overloads are provided for all integer types, which are treated as double. | (since C++11) |
Contents |
[edit]Parameters
| num | - | floating point or integer value |
[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::nearbyintstd::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
(C++11)(C++11) | nearest integer not greater than the given value (function) |
(C++11)(C++11)(C++11) | nearest integer not greater in magnitude than the given value (function) |
(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) |
(C++11)(C++11)(C++11) | nearest integer using current rounding mode (function) |
(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 | |
[edit]External links
| Fast ceiling of an integer division — StackOverflow |
