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CHAPTER 18. DISPATCHING WITH INHERITANCE using visual studio .net todisplay barcode data matrix on web,windows application EAN-14 a friend DataMatrix for .NET declaration is included in G). This visibility rule supports modular data-hiding, which is so important for achieving reliable systems.

In section (b), the private members of G are listed. Included here are data elds that exist for the subclass G but not for the superclass G, and functions (if any) that will be used only locally, by other functions de ned for G . Finally, additional public members of G are listed in section (c).

These must include all basic functions needed to operate on the subclass. Additional classes may be derived, similarly, from either G or G . Exhibit 18.

8 shows the C++ declarations that would implement part of the domain hierarchy from Exhibit 18.7. To nish implementation of this hierarchy, we need to supply de nitions for the remaining class, officer, and de nitions for all the functions declared in all the classes.

De nitions for these functions can be placed anywhere in the program, but good style dictates that they should be placed just after the class declaration. The functions that must be de ned are: employee::employee employee::print_paycheck employee::print_list employee::compute_pay salaried::compute_pay salaried::take_vacation hourly::hourly hourly::compute_pay hourly::record_time_card manager::manager manager::add_employee manager::print_list manager::do_payroll Although these method de nitions are outside the class declaration, the function methods themselves were declared within the class, and are class members with full access privileges. The placement of the function de nition (before or after the end of the class declaration) makes no di erence in the semantics the only di erence is practical; de nitions inside the class are expanded in-line, like macros, those outside are compiled as subroutines.

C++ functions can be overloaded, that is, a function name can have several de ning methods, belonging to several classes. For this reason, the full name of a function method must be used when we de ne it outside its class. Thus we must write hourly::compute_pay() and salaried::compute_pay, not simply compute_pay.

Representation and Visibility. A program object is created by instantiating a class, and this action is triggered either by a declaration or a new command. The result is a record with one eld for each of the variables (both public and private) within the class.

A derived class will be represented by the same type of record with elds added on the end. The names of the class variables are like the names of the elds of a record, except that more complexity is involved because of information-hiding. In a Pascal record, all the elds have the same visibility; that is, if one part is accessible in a given context, then all parts are accessible.

But in a C++ class, the elds corresponding to private members have visibility restricted to the class functions, while public members have broader visibility. When we make a derived class, elds for private members of the parent class will be part of the record and take up space, but the names of those elds will not be known within the derived class, and those elds will be inaccessible to new functions. However, the public functions of the base class become members of the derived class and can be used to manipulate these elds.

. 18.2. SUBDOMAINS AND CLASS HIERARCHIES. Exhibit 18. Data Matrix barcode for .NET 8.

Deriving classes in C++. Below are declarations for some of the classes described in Exhibit 18.7.

Exhibit 18.6 is a diagram of the relationships among these classes. This code is discussed throughout the rest of this chapter.

We presume that card and pay_data are previously de ned classes. class employee { char name[], soc_sec[13], *dept_code, *job_code; public: employee * link; employee(int) // The constructor; argument is name length. void print_paycheck; virtual pay_data compute_pay; virtual void print_list; void employee::print_empl() { cout << "Name: " << name << "\n\t" << soc_sec << "\tDept: " << dept_code << "\tJob: " << job_code << "\n"; } // End of class employee.

. class salar ied : public employee { int annual_salary, vacation_used; public: pay_data compute_pay(); void take_vacation(); }; // End of class salaried. class manager : salaried { employee* staff; public: void add_employee(); void print_list(); void do_payroll(); manager(); };. //The const gs1 datamatrix barcode for .NET ructor function. // End of class manager,.

class hourl y : public employee { float pay_rate, hours_worked, overtime; int vacation_used; public: pay_data compute_pay(); void record_time_card(card*); hourly(); }; // End of class hourly..
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