# std::asin

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
float asin( float arg ); | (1) |
double asin( double arg ); | (2) |
long double asin( long double arg ); | (3) |
double asin( Integral arg ); | (4) | (since C++11)

Computes the principal value of the arc sine of `arg`.

4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).

### Parameters

arg | - | value of a floating-point or Integral type

### Return value

If no errors occur, the arc sine of `arg` (arcsin(arg)) 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 `arg` 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 |arg| > 1, a domain error occurs and NaN is returned.
- if the argument is NaN, NaN is returned

### Example

Run this code

    #include <cmath>
    #include <iostream>
    #include <cerrno>
    #include <cfenv>
    #include <cstring>

    #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 | computes arc cosine (arccos(x)) (function)
atan | computes arc tangent (arctan(x)) (function)
atan2 | arc tangent, using signs to determine quadrants (function)
sin | computes sine (sin(x)) (function)
asin(std::complex) (C++11) | computes arc sine of a complex number (arcsin(z)) (function template)
asin(std::valarray) | applies the function std::asin to each element of valarray (function template)
C documentation for asin

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