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    std::literals::complex_literals::operator""i, operator""if, operator""il

    From cppreference.com
     
    C++
     
    Numerics library
     
    std::complex
     
    Defined in header <complex> 
    constexpr complex<double> operator""i( long double arg );
constexpr complex<double> operator""i( unsigned long long arg );
    		(1) (since C++14) 
    constexpr complex<float> operator""if( long double arg );
constexpr complex<float> operator""if( unsigned long long arg );
    		(2) (since C++14) 
    constexpr complex<long double> operator""il( long double arg );
constexpr complex<long double> operator""il( unsigned long long arg );
    		(3) (since C++14)

    Forms a std::complex literal representing an imaginary number.

    1) Forms a literal std::complex<double> with the real part zero and imaginary part arg.
    2) Forms a literal std::complex<float> with the real part zero and imaginary part arg.
    3) Forms a literal std::complex<long double> with the real part zero and imaginary part arg.

    Parameters

    arg - the value of the imaginary number

    Return value

    The std::complex literal with the real part zero and imaginary part arg.

    Notes

    These operators are declared in the namespace std::literals::complex_literals, where both literals and complex_literals are inline namespaces. Access to these operators can be gained with either:

    • using namespace std::literals,
    • using namespace std::complex_literals, or
    • using namespace std::literals::complex_literals.

    Even though if is a keyword in C++, it is a ud-suffix of the literal operator of the form operator ""if and in the literal expressions such as 1if or 1.0if because it is not separated by whitespace and is not a standalone token.

    Feature-test macro Value Std Feature
    __cpp_lib_complex_udls 201309L (C++14) User-Defined Literals for std::complex

    Possible implementation

    operator""i 
    constexpr std::complex<double> operator""i(unsigned long long d)
{
    return std::complex<double> {0.0, static_cast<double>(d)};
}

constexpr std::complex<double> operator""i(long double d)
{
    return std::complex<double> {0.0, static_cast<double>(d)};
}
    operator""if 
    constexpr std::complex<float> operator""if(unsigned long long d)
{
    return std::complex<float> {0.0f, static_cast<float>(d)};
}

constexpr std::complex<float> operator""if(long double d)
{
    return std::complex<float> {0.0f, static_cast<float>(d)};
}
    operator""il 
    constexpr std::complex<long double> operator""il(unsigned long long d)
{
    return std::complex<long double> {0.0L, static_cast<long double>(d)};
}

constexpr std::complex<long double> operator""il(long double d)
{
    return std::complex<long double> {0.0L, d};
}

    Example

    Run this code
    #include <complex>
#include <iostream>

int main()
{
    using namespace std::complex_literals;

    std::complex<double> c = 1.0 + 1i;
    std::cout << "abs" << c << " = " << std::abs(c) << '\n';

    std::complex<float> z = 3.0f + 4.0if;
    std::cout << "abs" << z << " = " << std::abs(z) << '\n';
}

    Output: 

    abs(1,1) = 1.41421
abs(3,4) = 5

    See also

    		 constructs a complex number
    (public member function) [edit]
    		assigns the contents
    (public member function) [edit]
    C documentation for I