acos(), acosf(), acosl()

Compute the arccosine of an angle

Synopsis:

#include <math.h>

double acos( double x );

float acosf( float x );

long double acosl( long double x );

Arguments:

x
The cosine for which you want to find the angle.

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:

These functions compute the arccosine (in radians) of x.

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

Returns:

The arccosine in the range [0.0, π].

If x is: These functions return: Errors:
Finite, but not in the range [-1,1] NaN FE_INVALID
±Inf NaN FE_INVALID
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 <fenv.h>
#include <stdlib.h>

int main( void )
{
    int except_flags;

    feclearexcept(FE_ALL_EXCEPT);

    printf( "acos(0.5) is %f\n", acos(0.5) );

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

produces the output:

1.047197

Classification:

C11, POSIX 1003.1

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