GradeBook.h: Defining a Class’s Interface with Function Prototypes

Header GradeBook.h (Fig. 3.11) contains another version of GradeBook’s class definition (lines 8–17). This version is similar to the one in Fig. 3.9, but the function definitions in Fig. 3.9 are replaced here with function prototypes (lines 11–14) that describe the class’s public interface without revealing the class’s member-function implementations. A function prototype is a declaration of a function that tells the compiler the function’s name, its return type and the types of its parameters. Also, the header still specifies the class’s private data member (line 16) as well. Again, the compiler must know the data members of the class to determine how much memory to reserve for each object of the class. Including the header GradeBook.h in the client code (line 5 of Fig. 3.13) provides the compiler with the information it needs to ensure that the client code calls the member functions of class GradeBook correctly.

The function prototype in line 11 (Fig. 3.11) indicates that the constructor requires one string parameter. Recall that constructors don’t have return types, so no return type appears in the function prototype. Member function setCourseName’s function prototype indicates that setCourseName requires a string parameter and does not return a value (i.e., its return type is void). Member function getCourseName’s function prototype indicates that the function does not require parameters and returns a string. Finally, member function displayMessage’s function prototype (line 14) specifies that displayMessage does not require parameters and does not return a value. These function prototypes are the same as the first lines of the corresponding function definitions in Fig. 3.9, except that the parameter names (which are optional in prototypes) are not included and each function prototype must end with a semicolon.