acos, acosf, acosl

Parameters

Return value

If no errors occur, the arc cosine of arg ( arccos(arg) ) in the range [0 ; π] , is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling .

Domain error occurs if arg is outside the range [-1.0; 1.0] .

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

• If the argument is +1 , the value +0 is returned;
• If |arg| > 1 , a domain error occurs and NaN is returned;
• if the argument is NaN, NaN is returned.

Example

#include <errno.h>
#include <fenv.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
 
#ifndef __GNUC__
#pragma STDC FENV_ACCESS ON
#endif
 
int main(void)
{
    printf("acos(-1) = %f\n", acos(-1));
    printf("acos(0.0) = %f 2*acos(0.0) = %f\n", acos(0), 2 * acos(0));
    printf("acos(0.5) = %f 3*acos(0.5) = %f\n", acos(0.5), 3 * acos(0.5));
    printf("acos(1) = %f\n", acos(1));
 
    // error handling
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("acos(1.1) = %f\n", acos(1.1));
    if (errno == EDOM)
        perror("    errno == EDOM");
    if (fetestexcept(FE_INVALID))
        puts("    FE_INVALID raised");
}

acos(-1) = 3.141593
acos(0.0) = 1.570796 2*acos(0.0) = 3.141593
acos(0.5) = 1.047198 3*acos(0.5) = 3.141593
acos(1) = 0.000000
acos(1.1) = nan
    errno == EDOM: Numerical argument out of domain
    FE_INVALID raised

References

See also