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

4) Type-generic macro: If arg has type long double, ceill is called. Otherwise, if arg has integer type or the type double, ceil is called. Otherwise, ceilf is called.

Parameters

Return value

If no errors occur, the smallest integer value not less than arg, that is ⌈arg⌉, 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 arg is ±∞, it is returned, unmodified.
• If arg is ±0, it is returned, unmodified.
• If arg is NaN, NaN is returned.

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 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 <fenv.h>
#include <math.h>
#pragma STDC FENV_ACCESS ON

double ceil(double x)
{
    double result;
    int save_round = fegetround();
    fesetround(FE_UPWARD);
    result = rint(x); // or nearbyint
    fesetround(save_round);
    return result;
}

Example

#include <math.h>
#include <stdio.h>

int main(void)
{
    printf("ceil(+2.4) = %+.1f\n", ceil(2.4));
    printf("ceil(-2.4) = %+.1f\n", ceil(-2.4));
    printf("ceil(-0.0) = %+.1f\n", ceil(-0.0));
    printf("ceil(-Inf) = %+f\n",   ceil(-INFINITY));
}

ceil(+2.4) = +3.0
ceil(-2.4) = -2.0
ceil(-0.0) = -0.0
ceil(-Inf) = -inf

References

See also