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

Defined in header `<cmath>`
	(1)
float asin ( float num ); double asin ( double num ); long double asin ( long double num );			(until C++23)
/* floating-point-type / asin ( / floating-point-type */ num );			(since C++23) (constexpr since C++26)
float asinf( float num );		(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 > double asin ( Integer num );		(A)	(constexpr since C++26)

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 treated as double.

(since C++11)

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

Compiler support
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Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
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Concepts library (C++20)
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Diagnostics library
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Execution support library (C++26)
Technical specifications
Symbols index
External libraries

acosacosfacosl (C++11)(C++11)	computes arc cosine (\({\small\arccos{x}}\) $arccos(x)$ ) (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)
sinsinfsinl (C++11)(C++11)	computes sine (\({\small\sin{x}}\) $sin(x)$ ) (function)
asin(std::complex) (C++11)	computes arc sine of a complex number (\({\small\arcsin{z}}\) $arcsin(z)$ ) (function template)
asin(std::valarray)	applies the function std::asin to each element of valarray (function template)
C documentation for asin