std::acos, std::acosf, std::acosl

 

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Defined in header <cmath>
	(1)
float       acos (float num ); double      acos (double num ); longdouble acos (longdouble num );			(until C++23)
/*floating-point-type*/             acos (/*floating-point-type*/ num );			(since C++23) (constexpr since C++26)
float       acosf(float num );		(2)	(since C++11) (constexpr since C++26)
longdouble acosl(longdouble num );		(3)	(since C++11) (constexpr since C++26)
SIMD overload(since C++26)
Defined in header <simd>
template</*math-floating-point*/ V > constexpr/*deduced-simd-t*/<V>             acos (const V& v_num );		(S)	(since C++26)
Additional overloads(since C++11)
Defined in header <cmath>
template<class Integer > double      acos ( Integer num );		(A)	(constexpr since C++26)

1-3) Computes the principal value of the arc cosine of num. The library provides overloads of std::acos for all cv-unqualified floating-point types as the type of the parameter.(since C++23)

S) The SIMD overload performs an element-wise std::acos on v_num. (See math-floating-point and deduced-simd-t for their definitions.)

(since C++26)

A) Additional overloads are provided for all integer types, which are treated as double.

(since C++11)

Parameters

num

-

floating-point or integer value

Return value

If no errors occur, the arc cosine of num (arccos(num)) 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 num 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 |num| > 1, a domain error occurs and NaN is returned.
• if the argument is NaN, NaN is returned.

Notes

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::acos(num) has the same effect as std::acos(static_cast<double>(num)).

Example

Run this code

#include <cerrno>#include <cfenv>#include <cmath>#include <cstring>#include <iostream>   // #pragma STDC FENV_ACCESS ON   int main(){std::cout<<"acos(-1) = "<< std::acos(-1)<<'\n'<<"acos(0.0) = "<< std::acos(0.0)<<'\n'<<"2*acos(0.0) = "<<2* std::acos(0)<<'\n'<<"acos(0.5) = "<< std::acos(0.5)<<'\n'<<"3*acos(0.5) = "<<3* std::acos(0.5)<<'\n'<<"acos(1) = "<< std::acos(1)<<'\n';   // error handlingerrno=0;std::feclearexcept(FE_ALL_EXCEPT);   std::cout<<"acos(1.1) = "<< std::acos(1.1)<<'\n';   if(errno==EDOM)std::cout<<" errno == EDOM: "<<std::strerror(errno)<<'\n';if(std::fetestexcept(FE_INVALID))std::cout<<" FE_INVALID raised"<<'\n';}

Output:

acos(-1) = 3.14159 acos(0.0) = 1.5708 2*acos(0.0) = 3.14159 acos(0.5) = 1.0472 3*acos(0.5) = 3.14159 acos(1) = 0 acos(1.1) = nan errno == EDOM: Numerical argument out of domain FE_INVALID raised

See also

asinasinfasinl (C++11)(C++11)	computes arc sine (\({\small\arcsin{x}}\)arcsin(x)) (function)
atanatanfatanl (C++11)(C++11)	computes arc tangent (\({\small\arctan{x}}\)arctan(x)) (function)
atan2atan2fatan2l (C++11)(C++11)	arc tangent, using signs to determine quadrants (function)
coscosfcosl (C++11)(C++11)	computes cosine (\({\small\cos{x}}\)cos(x)) (function)
acos(std::complex) (C++11)	computes arc cosine of a complex number (\({\small\arccos{z}}\)arccos(z)) (function template)
acos(std::valarray)	applies the function std::acos to each element of valarray (function template)
C documentation for acos