std::ceil, std::ceilf, std::ceill
| Defined in header <cmath>
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||
| (1) | ||
float ceil ( float num ); double ceil ( double num ); long double ceil ( long 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) |
long double ceill( long double num ); |
(3) | (since C++11) (constexpr since C++23) |
| SIMD overload (since C++26) |
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| Defined in header <simd>
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template< /*math-floating-point*/ V > constexpr /*deduced-simd-t*/<V> ceil ( const V& v_num ); |
(S) | (since C++26) |
| Additional overloads (since C++11) |
||
| Defined in header <cmath>
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template< class Integer > double ceil ( Integer num ); |
(A) | (constexpr since C++23) |
num. The library provides overloads of 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) |
Parameters
| num | - | floating point or integer value |
Return value
If no errors occur, the smallest integer value not less than num, that is ⌈num⌉, is returned.
numError 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
numis ±∞, it is returned unmodified. - If
numis ±0, it is returned, unmodified. - If
numis NaN, NaN is returned.
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)).
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
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
| |
External links
| Fast ceiling of an integer division — StackOverflow |