NAME¶

std::asin,std::asinf,std::asinl - std::asin,std::asinf,std::asinl

Synopsis¶

Defined in header <cmath>
float asin ( float num );

double asin ( double num ); (until C++23)

long double asin ( long double num );
/* floating-point-type */ (since C++23)
asin ( /* floating-point-type */ num ); (constexpr since C++26)
float asinf( float num ); (1) (2) (since C++11)
(constexpr since C++26)
long double asinl( long double num ); (3) (since C++11)
(constexpr since C++26)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++26)
double asin ( Integer num );

1-3) Computes the principal value of the arc sine of num.
The library provides overloads of std::asin 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 (since C++11)
treated as double.

Parameters¶

num - floating-point or integer value

Return value¶

If no errors occur, the arc sine of num (arcsin(num)) in the range [-

π
2

, +

π
2

], 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 ±0, it is returned unmodified.
* 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::asin(num) has the same effect as std::asin(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 << "asin(1.0) = " << asin(1) << '\n'
<< "2*asin(1.0) = " << 2 * asin(1) << '\n'
<< "asin(-0.5) = " << asin(-0.5) << '\n'
<< "6*asin(-0.5) =" << 6 * asin(-0.5) << '\n';

// special values
std::cout << "asin(0.0) = " << asin(0) << " asin(-0.0)=" << asin(-0.0) << '\n';

// error handling
errno = 0;
std::feclearexcept(FE_ALL_EXCEPT);

std::cout << "asin(1.1) = " << asin(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';
}

Possible output:¶

asin(1.0) = 1.5708
2*asin(1.0) = 3.14159
asin(-0.5) = -0.523599
6*asin(-0.5) = -3.14159
asin(0.0) = 0 asin(-0.0)=-0
asin(1.1) = nan
errno == EDOM: Numerical argument out of domain
FE_INVALID raised

See also¶

acos
acosf computes arc cosine (\({\small\arccos{x}}\)arccos(x))
acosl (function)
(C++11)
(C++11)
atan
atanf computes arc tangent (\({\small\arctan{x}}\)arctan(x))
atanl (function)
(C++11)
(C++11)
atan2
atan2f arc tangent, using signs to determine quadrants
atan2l (function)
(C++11)
(C++11)
sin
sinf computes sine (\({\small\sin{x}}\)sin(x))
sinl (function)
(C++11)
(C++11)
asin(std::complex) computes arc sine of a complex number
(C++11) (\({\small\arcsin{z}}\)arcsin(z))
(function template)
asin(std::valarray) applies the function std::asin to each element of valarray
(function template)
C documentation for
asin