How to check for NULL(empty/0) strings if I don't have access to the string variables

Edit: Sorry if I did not specify, I can NOT change these given structs and classes. So I can not make get/set functions for the fields in the Student struct and Grade class.

This is an assignment of two parts, part 1 was relatively easy and has a struct like so:

Part1 (Student.h) Can NOT be changed

const unsigned int MAX_GRADES= 5;

struct Student
{
    char* studentText;
    unsigned int numSubjects;
    Grade grades[MAX_ANSWERS];
    Student():studentText(0){};
    ~Student();
};

Then in part 2 that has changed to:

Part2 (Student.h) Can NOT be changed

struct Student
    {
            static const unsigned int MAX_GRADES = 5;
            Student():studentText(0){;}
            Student(char*,unsigned int,Grade*);
            Student(Student&);
            ~Student();
            friend ostream& operator<<(ostream&,Student&);
    private:
        char* studentText;
        unsigned int numSubjects;
        Grade grades[MAX_GRADES];
    };

Grade is a class with also private string:

Part2 (Grade.h) Can NOT be changed

 class Grade
    {
        char* subject;
        bool pass;
    public: 
        Grade():subject(0){;}
        Grade(char*,bool);
        Grade(Grade&);
        ~Grade();
        Grade& operator=(Grade&);
        friend ostream& operator<<(ostream&,Grade&);
    };

The variable studentText that I used to use to check if a Student is empty inside students[] by using:

if(students[j]->studentText==0)

Has now become private and I can not reach it from my main. Can anyone point me to the right direction.

Can I use the overloaded << to somehow get studentText and test if it is 0.

Thanks in advance