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ceil, ceilf, ceill

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
Types
(C99)(C99)    

(C99)(C99)    

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(C99)
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(C99)(C99)(C99)(C23)
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Nearest integer floating-point operations
ceil
(C99)(C99)(C99)
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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.

Contents

[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
math-ceil.svg
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 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;
}

[edit] 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));
}

Possible output:

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

[edit] References

  • C23 standard (ISO/IEC 9899:2023):
  • 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

[edit] See also

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