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

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


arg - the value of the imaginary number

Return value

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


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};


#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';


abs(1,1) = 1.41421

See also

constructs a complex number
(public member function)
assigns the contents
(public member function)

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