Code inspecting Stroustrup (TC++PL4)

TC++PL4 is now on my desk and carefully reading it I have to say that even Stroustrup makes stupid mistakes in his classes implementations.

He illustrates a typical Vector implementation (pag. 73):

    class Vector {
    private:
        double* elem;
        int sz;
    public:
        Vector(int s);
        ~Vector() { delete [] elem; }
        
        Vector(const Vector& a);
        Vector& operator=(const Vector& a);

        double& operator[](int i);
        const double& operator[](int i) const;

        int size() const;
    };

and given the fact this class needs a copy constructor implemented he "implements" it (pag. 74):

     Vector::Vector(const Vector& a)
         :elem{new double[sz]},
          sz{a.sz}
     {
         for (int i = 0; i != sz; ++i)
         elem[i] = a.elem[i];
     }

as you can see the elem vector is built with a size retrieved from a not yet initialized variable, being it defined at page 74 I had my last hope flipping the page and checking at page 73 if "int sz" was declared before "double* elem" but it was not the case.

I'm sad.