3.8. Validating Data with set Functions

In Section 3.4, we introduced set functions for allowing clients of a class to modify the value of a private data member. In Fig. 3.5, class GradeBook defines member function setCourseName to simply assign a value received in its parameter name to data member courseName. This member function does not ensure that the course name adheres to any particular format or follows any other rules regarding what a “valid” course name looks like. Suppose that a university can print student transcripts containing course names of only 25 characters or less. If the university uses a system containing GradeBook objects to generate the transcripts, we might want class GradeBook to ensure that its data member courseName never contains more than 25 characters. The program of Figs. 3.15–3.17 enhances class GradeBook’s member function setCourseName to perform this validation (also known as validity checking).

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 1   // Fig. 3.15: GradeBook.h
 2   // GradeBook class definition presents the public interface of
 3   // the class. Member-function definitions appear in GradeBook.cpp.
 4   #include <string> // program uses C++ standard string class
 5
 6   // GradeBook class definition
 7   class GradeBook
 8   {
 9   public:
10      explicit GradeBook( std::string ); // constructor initialize courseName
11      void setCourseName( std::string ); // sets the course name
12      std::string getCourseName() const; // gets the course name
13      void displayMessage() const; // displays a welcome message
14   private:
15      std::string courseName; // course name for this GradeBook
16   }; // end class GradeBook

Fig. 3.15. GradeBook class definition presents the public interface of the class.

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