operator!=

template<class T>
    bool operator!=(const complex<T>& lhs, const complex<T>& rhs);
template<class T>
    bool operator!=(const complex<T>& lhs, const T& rhs);
template<class T>
    bool operator!=(const T& lhs, const complex<T>& rhs);

The operators each return true only if real(lhs) != real(rhs) || imag(lhs) != imag(rhs).