According to the C++ Standard
6 An operator function shall either be a non-static member function or be a non-member function and have at least one parameter whose type is a class, a reference to a class, an enumeration, or a reference to an enumeration.
So you may not define operator <<
as a static mamber function of the class.
Nevertheless inside the definition of the operator you may use static member functions.
For example
#include <iostream>
class A
{
private:
int x = 10;
public:
static std::ostream & out( std::ostream &os, const A &a )
{
return ( os << a.x );
}
};
std::ostream & operator <<( std::ostream &os, const A &a )
{
return ( A::out( os, a ) );
}
int main()
{
A a;
std::cout << a << std::endl;
return 0;
}
Opposite to C++ in C# operator functions are defined as static.:)