std::ceil, std::ceilf, std::ceill
| Defined in header <cmath>
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| (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) |
| long double ceill( long double num ); |
(3) | (since C++11) (constexpr since C++23) |
| Additional overloads (since C++11) |
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| Defined in header <cmath>
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||
| 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)|
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.
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.
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
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External links
| Fast ceiling of an integer division — StackOverflow |