ceil, ceilf, ceill

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Defined in header <math.h>
float       ceilf( float arg );
 (1) (since C99)
double      ceil( double arg );
 (2)
long double ceill( long double arg );
 (3) (since C99)
Defined in header <tgmath.h>
#define ceil( arg )
 (4) (since C99)
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

arg - floating-point value

Return value

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

Return value
math-ceil.svg
Argument

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

Run this code
#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));
}

Possible output: 

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

References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.12.9.1 The ceil functions (p: TBD)
  • 7.25 Type-generic math <tgmath.h> (p: TBD)
  • F.10.6.1 The ceil functions (p: TBD)
  • C17 standard (ISO/IEC 9899:2018):
  • 7.12.9.1 The ceil functions (p: TBD)
  • 7.25 Type-generic math <tgmath.h> (p: TBD)
  • F.10.6.1 The ceil functions (p: TBD)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.12.9.1 The ceil functions (p: 251)
  • 7.25 Type-generic math <tgmath.h> (p: 373-375)
  • F.10.6.1 The ceil functions (p: 526)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12.9.1 The ceil functions (p: 231-232)
  • 7.22 Type-generic math <tgmath.h> (p: 335-337)
  • F.9.6.1 The ceil functions (p: 462-463)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 4.5.6.1 The ceil function

See also

(C99)(C99)
 computes largest integer not greater than the given value
(function)
(C99)(C99)(C99)
 rounds to nearest integer not greater in magnitude than the given value
(function)
(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
 rounds to nearest integer, rounding away from zero in halfway cases
(function)
(C99)(C99)(C99)
 rounds to an integer using current rounding mode
(function)
(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
 rounds to an integer using current rounding mode with
exception if the result differs
(function)
C++ documentation for ceil
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