In C++, the protected access specifier is one of three access specifiers (the others being public and private) that determine the level of access to class members (data and functions) from outside the class. The protected access specifier provides a level of access that is between public and private. Members declared as protected can be accessed by the derived class, but not by the code that uses the object of the class or the object itself.

In C++, there are three types of inheritance: public, private, and protected. Each type of inheritance specifies how the base class members are accessible to the derived class. Here is an overview of how the protected access specifier works with each type of inheritance:

1. Public Inheritance:
   In public inheritance, the public and protected members of the base class become public and protected members of the derived class, respectively. The private members of the base class are not accessible to the derived class. Here is an example:

class Base {
public:
    int x;
protected:
    int y;
private:
    int z;
};

class Derived : public Base {
    // x is public in Derived
    // y is protected in Derived
    // z is not accessible in Derived
};

2. Private Inheritance:
   In private inheritance, the public and protected members of the base class become private members of the derived class. The private members of the base class are not accessible to the derived class. Here is an example:

class Base {
public:
    int x;
protected:
    int y;
private:
    int z;
};

class Derived : private Base {
    // x is private in Derived
    // y is private in Derived
    // z is not accessible in Derived
};

3. Protected Inheritance:
   In protected inheritance, the public and protected members of the base class become protected members of the derived class. The private members of the base class are not accessible to the derived class. Here is an example:

class Base {
public:
    int x;
protected:
    int y;
private:
    int z;
};

class Derived : protected Base {
    // x is protected in Derived
    // y is protected in Derived
    // z is not accessible in Derived
};

In all three types of inheritance, the protected members of the base class are inherited by the derived class as protected. This means that they can be accessed by the derived class, but not by any code that uses the object of the class or the object itself.

Overall, the protected access specifier is useful for implementing certain design patterns and for controlling access to the members of the derived class.