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

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< cpp‎ | numeric‎ | 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 using namespace std::literals, using namespace std::complex_literals, and 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.

### Possible implementation

First version

    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)};
    }

Second version

    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)};
    }

Third version

    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 <iostream>
    #include <complex>

    int main()
    {
        using namespace std::complex_literals;
        std::complex<double> c = 1.0 + 1i;
        std::cout << "abs" << c << " = " << abs(c) << '\n';
    }

Output:

    abs(1,1) = 1.41421

### See also

(constructor) | constructs a complex number (public member function)
operator= | assigns the contents (public member function)
C documentation for I

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