ceil(), ceilf(), ceill()

Updated: October 26, 2022

Round up a value to the next integer

Synopsis:

#include <math.h>

double ceil( double x );

float ceilf( float x );

long double ceill( long double x );

Arguments:

x
The value you want to round.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The ceil(), ceilf(), and ceill() functions round the value of x up to the next integer (rounding towards the “ceiling”).

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The smallest integer x with the same sign as x.

If x is: These functions return: Errors:
±0.0 x
±Inf x
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

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

int main( void )
{
    printf( "%f %f %f %f %f\n", ceil( -2.1 ), 
      ceil( -2. ), ceil( 0.0 ), ceil( 2. ), 
      ceil( 2.1 ) );

    return EXIT_SUCCESS;
}

produces the output:

-2.000000 -2.000000 0.000000 2.000000 3.000000

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes