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

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< cpp‎ | numeric‎ | math

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

### See also

acos acosf acosl (C++11)(C++11) | computes arc cosine (\({\small\arccos{x} }\)arccos(x)) (function)
atan atanf atanl (C++11)(C++11) | computes arc tangent (\({\small\arctan{x} }\)arctan(x)) (function)
atan2 atan2f atan2l (C++11)(C++11) | arc tangent, using signs to determine quadrants (function)
sin sinf sinl (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)

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