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Often errors happen at boundaries between domains. In source code, decision statements determine the boundaries. If a decision statement is written as x<1 instead of x<0, the boundary has shifted. If a decision is written x=<1, then the boundary, x=1, is in the true subdomain. In the terminology of boundary testing, we say that the on tests are in the true domain and the o tests are values of x greater than 1 and are in the false domain. If a decision is written x<1 instead of x=<1, then the boundary, x=1, is now in the false subdomain instead of in the true subdomain. Boundary testing is aimed at ensuring that the actual boundary between two subdomains is as close as possible to the speci ed boundary. Thus, test cases are selected on the boundary and o the boundary as close as reasonable to the boundary. The standard boundary test is to do two on tests as far apart as possible and one o test close to the middle of the boundary. Figure 10-3 shows a simple boundary. The arrow indicates that the on tests of the boundary are in the subdomain below the boundary. The two on tests are at the ends of the boundary and the o test is just above the boundary halfway along the boundary.

class Student : p u b l i c P e r s o n { public: Student(char* n, int s=O, char* i="") : Person(n, s), id(i), credits(O) { } void setDOM(int m, int d, int y) { dom.setDate(m, d, y); } void printDOM() { tout << dom; } private: String id; // student identification number Date dom; // date of matriculation int credits; // course credits float gpa; // grade-point average

The Student class inherits all the pub1 ic functionality of the Person class, including the Person ( ) constructor which it uses in its constructor to initialize name in the Person class. Note that this is a private member of the Person class, so it could not be accessed directly. Here is a test driver for the Student class:

#include "Student.h"

main0 -t Student x("Ann Jones", "219360061"); x.setDOB(5, 13, 1977); x.setDOM(8, 29, 1995); x.printName() ; x.printDOB tout CC "\n\t Born: "; > ; tout << "\n\tMatriculated: '; x.printDOM > ; )

Fig. 10-3.

tout CC endl;

CHAP. 1 l]

11.4 protected CLASS MEMBERS The Student class in Section 11.3 has a significant problem: it cannot directly access the private data members of its Person superclass: name, nationality, DOB, DOD, and sex. The lack of access on the first four of these is not serious because these can be written and read through the Person class s constructor and public access functions. However, there is no way to write or read a student's sex. One way to overcome this problem would be to make sex a data member of the Student class. But that is unnatural: sex is an attribute that all Person objects have, not just Students. A better solution is to change the private access specifier to protected in the Person class. That will allow access to these data members from derived classes.

EXAMPLE 11.5 The Person Class with protected Data Members These are the same class definitions that were given in Example 11.3 and Example 11.4 except that the private access specifier has been changed to pro tee ted, and we have added the access function printSex to the Student class: #include "String.h" #include "Date.h" class Person { public: Person(char* n="", int s=O, char* nat=YJ.S.A.") : name(n), sex(s), nationality(nat) { > void setDOB(int m, int d, int y) { dob.setDate(m, d, y); > void setDOD(int m, int d, int y) { dod.setDate(m, d, y); > void printName { tout << name; > void printNationality { tout << nationality; > void printDOB() { tout << dob; > void printDOD() { tout << dod; } protected: String name, nationality; // date of birth, date of death Date dob, dod; //o= female, 1 = male * int sex; >; class Student : public Person { public: Student(char* n, int s=O, char* i=""> : Person(n, s), id(i), credits(O) { } void setDOM(int m, int d, int y) { dom.setDate(m, d, y); > void printDOM() { tout << dom; } v o i d printSex { tout CC ( s e x male : f e m a l e ) ; } protected: // student identification number String id; // date of matriculation Date dom; // course credits int credits; // grade-point average float gpa; >;