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# std::ceil

From cppreference.com
< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
float ceil( float arg ); | (1) |
double ceil( double arg ); | (2) |
long double ceil( long double arg ); | (3) |
double ceil( Integral arg ); | (4) | (since C++11)

1-3) Computes the smallest integer value not less than `arg`.
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).

### [edit] Parameters

arg | - | floating point value

### [edit] Return value

If no errors occur, the smallest integer value not less than `arg`, that is ⌈arg⌉, is returned.

Return value
Argument

### [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 `arg` is ±∞, it is returned unmodified
- If `arg` is ±0, it is returned, unmodified
- If arg is NaN, NaN is returned

### [edit] Notes

FE_INEXACT may be (but isn't 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.

This function (for double argument) behaves as if (except for the freedom to not raise FE_INEXACT) implemented by

    #include <cmath>
    #include <cfenv>
    #pragma STDC FENV_ACCESS ON
    double ceil(double x)
    {
        double result;
        int save_round = std::fegetround();
        std::fesetround(FE_UPWARD);
        result = std::rint(x); // or std::nearbyint
        std::fesetround(save_round);
        return result;
    }

### [edit] 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

### [edit] See also

floor | nearest integer not greater than the given value (function) [edit]
trunc (C++11) | nearest integer not greater in magnitude than the given value (function) [edit]
round lround llround (C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function) [edit]
nearbyint (C++11) | nearest integer using current rounding mode (function) [edit]
rint lrint llrint (C++11)(C++11)(C++11) | nearest integer using current rounding mode with exception if the result differs (function) [edit]
C documentation for ceil

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