In-Class Exercise
Derived Class with a Resource
This exercise upgrades an inheritance hierarchy to manage
objects that access resources through a derived class.
Given Information
The following code is a solution to the Handout on
Functions in a Hierarchy.
Client Module
The client program is listed on the left and the output is shown on the right
// Functions in a Hierarchy
// h13.cpp
#include <iostream>
#include "Employee.h"
int main() {
Employee employee(1234, "Jane Doe", 15.50);
Person person("John Doe");
employee.display(std::cout);
std::cout << std::endl;
person.display(std::cout);
std::cout << std::endl;
}
|
Jane Doe (1234) $15.50
John Doe
|
Employee Module
Employee.h
// Functions in a Hierarchy
// Employee.h
#include <iostream>
const int MAX_NAME = 20;
class Person {
char name[MAX_NAME + 1];
public:
Person();
Person(const char*);
void display(std::ostream&) const;
};
class Employee : public Person {
int no;
double rate;
public:
Employee();
Employee(int, const char*, double);
void display(std::ostream&) const;
};
|
Employee.cpp
// Functions in a Hierarchy
// Employee.cpp
#include <iomanip>
#include <cstring>
#include "Employee.h"
Person::Person() {
name[0] = '\0';
}
Person::Person(const char* n) {
strncpy(name, n, MAX_NAME);
name[MAX_NAME] = '\0';
}
void Person::display(std::ostream& os) const {
if (name[0] != '\0')
os << name << " ";
}
const int MIN_WAGE = 10.25;
const int SAFE_NUM = 0;
Employee::Employee() {
// safe empty state
no = SAFE_NUM;
rate = MIN_WAGE;
}
Employee::Employee(int n, const char* nm, double r)
: Person(nm)
{
if (n > SAFE_NUM && r >= MIN_WAGE) {
no = n;
rate = r;
}
else { // safe empty state
Employee temp;
*this = temp;
}
}
void Employee::display(std::ostream& os) const {
if (no != SAFE_NUM) {
Person::display(os);
os << std::fixed << std::setprecision(2);
os << "(" << no << ") $" << rate;
}
else
os << "no data available";
}
|
Your Task
Upgrade the Employee class by adding the name
of the employee's department. Assume no limit on the number
of characters in that name.
Client Module
The client program that uses your upgraded class is
listed on the left and the results are listed on the right:
// Derived Class with a Resource
// h14.cpp
#include <iostream>
#include "Employee.h"
int main() {
Employee employee(1234, "Jane Doe", 15.50,
"Sales");
Person person("John Doe");
employee.display(std::cout);
std::cout << std::endl;
person.display(std::cout);
std::cout << std::endl;
}
|
Jane Doe (1234) $15.50 Sales
John Doe
|
Employee Module
The Employee module accepts the address of
a C-style string containing the department's name through the fourth parameter
of a four-argument constructor. The name of the department may be of
any length. You need to allocate dynamic memory for a copy of the string
and define a copy constructor, assignment operator, and destructor for the
derived class.
Call the base class' copy constructor from the derived class'
copy constructor and the base class' assignment operator from
the derived class' assignment operator. Finally, output
the department name from the display()
member function.
Employee.h
// Derived Class with a Resource
// Employee.h
#include <iostream>
const int MAX_NAME = 20;
class Person {
char name[MAX_NAME + 1];
public:
Person();
Person(const char*);
void display(std::ostream&) const;
};
class Employee : public Person {
int no;
double rate;
public:
Employee();
Employee(int, const char*, double, );
void display(std::ostream&) const;
};
|
Employee.cpp
// Derived Class with a Resource
// Employee.cpp
#include <iomanip>
#include <cstring>
#include "Employee.h"
Person::Person() {
name[0] = '\0';
}
Person::Person(const char* n) {
strncpy(name, n, MAX_NAME);
name[MAX_NAME] = '\0';
}
void Person::display(std::ostream& os) const {
if (name[0] != '\0')
os << name << " ";
}
const int MIN_WAGE = 10.25;
const int SAFE_NUM = 0;
Employee::Employee() {
// safe empty state
no = SAFE_NUM;
rate = MIN_WAGE;
}
Employee::Employee(int n, const char* nm, double r, )
: Person(nm)
{
if (n > SAFE_NUM && r >= MIN_WAGE) {
no = n;
rate = r;
}
else { // safe empty state
Employee temp;
*this = temp;
}
}
void Employee::display(std::ostream& os) const {
if (no != SAFE_NUM) {
Person::display(os);
os << std::fixed << std::setprecision(2);
os << "(" << no << ") $" << rate;
}
else
os << "no data available";
}
|
|
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