# std::ceil, std::ceilf, std::ceill

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (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) |  |
Defined in header `<simd>` |  |
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>` |  |
template< class Integer > double ceil ( Integer num ); | (A) | (constexpr since C++23)

1-3) Computes the least integer value not less than 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.

    (See `math-floating-point` and `deduced-simd-t` for their definitions.)

(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.

Return value
num

### 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

Run this code

    #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

floorfloorffloorl (C++11)(C++11) | nearest integer not greater than the given value (function)
trunctruncftruncl (C++11)(C++11)(C++11) | nearest integer not greater in magnitude than the given value (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (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)
nearbyintnearbyintfnearbyintl (C++11)(C++11)(C++11) | nearest integer using current rounding mode (function)
rintrintfrintllrintlrintflrintlllrintllrintfllrintl (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

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