From cppreference.com
Defined in header
floatacos(floatnum);doubleacos(doublenum);longdoubleacos(longdoublenum); (1)(until C++23)/*floating-point-type*/acos(/*floating-point-type*/num);(since C++23)
(constexpr since C++26)floatacosf(floatnum); (2)(since C++11)
(constexpr since C++26)longdoubleacosl(longdoublenum); (3)(since C++11)
(constexpr since C++26)
(since C++26)
Defined in header
template</*math-floating-point*/V>constexpr/*deduced-simd-t*/<V>acos(constV&v_num); (S) (since C++26)
(since C++11)
Defined in header
template<classInteger>doubleacos(Integernum); (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)
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
.
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 ONintmain(){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
(C++11)(C++11)
computes arc sine (arcsin(x))
(function)
(C++11)(C++11)
computes arc tangent (arctan(x))
(function)
(C++11)(C++11)
arc tangent, using signs to determine quadrants
(function)
(C++11)(C++11)
computes cosine (cos(x))
(function)
(C++11)
computes arc cosine of a complex number (arccos(z))
(function template)
applies the function
to each element of valarray
(function template)
for acos