Declaring a namespace as a friend of a class

I was wondering if there is a way such that we make all functions defined within a specific namespace friend with a class?

In particular, I have a class, for example:

class C {
    private:
        // ...
    public:
        // ...

        friend C* B::f1(C*);
        friend C* B::f2(C*);
        friend C* B::f3(C*);
        friend C* B::f4(C*);
        friend C* B::f5(C*);
};

and a namespace B as:

namespace B {
    C* f1(C* x);
    C* f2(C* x);
    C* f3(C* x);
    C* f4(C* x);
    C* f5(C* x);
};

Now, I would prefer to avoid writing 5 lines in the class definition to make all five functions of the namespace B friend with class C and just tell the compiler that all of the functions defined within the namespace B are friends with the class C (i.e. can access its private members).

A quick fix I guess is to change the namespace to a class and define the functions as its static members and then declare the class B as a friend of class C. However, out of curiosity I was wondering if such thing is possible with namespaces as well or not?

Thanks in advance.