float acosf( float arg );
(1) (since C99)double acos( double arg );
(2)long double acosl( long double arg );
(3) (since C99)_Decimal32 acosd32( _Decimal32 arg );
(4) (since C23)_Decimal64 acosd64( _Decimal64 arg );
(5) (since C23)_Decimal128 acosd128( _Decimal128 arg );
(6) (since C23)#define acos( arg )
(7) (since C99)1-6) Computes the principal value of the arc cosine of arg.
7)Type-generic macro: If the argument has type
long double,
(3)(
acosl
) is called. Otherwise, if the argument has integer type or the type
double,
(2)(
acos
) is called. Otherwise,
(1)(
acosf
) is called. If the argument is complex, then the macro invokes the corresponding complex function (
cacosf,
cacos,
cacosl).
The functions (4-6) are declared if and only if the implementation predefines __STDC_IEC_60559_DFP__ (i.e. the implementation supports decimal floating-point numbers).
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.
[edit] Error handlingErrors 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):
+0 is returned;#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");
}
Possible output:
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[edit] References
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