Chapter 15-Virtual Functions

Example-parent1.cpp, Page no-618

class Father:
    __name=[chr]*20
    def __init__(self, fname):
        self.__name=fname
    def show(self):
        print "Father name:", self.__name
class Son(Father):
    __name=[chr]*20
    def __init__(self, sname, fname):
        Father.__init__(self, fname)
        self.__name=sname
    def show(self):
        print "Son name:", self.__name
fp=[Father]
f1=Father("Eshwarappa")
fp=f1
fp.show()
s1=Son("Rajkumar", "Eshwarappa")
fp=s1
Father.show(fp)

Father name: Eshwarappa
Father name: Eshwarappa

Example-parent1.cpp, Page no-619

class Father():
    __name=[chr]*20
    def __init__(self, fname):
        self.__name=fname
    def show(self):
        print "Father name:", self.__name
class Son(Father):
    __name=[chr]*20
    def __init__(self, sname, fname):
        Father.__init__(self, fname)
        self.__name=sname
    def show(self):
        print "Son name:", self.__name
fp=[Father]
f1=Father("Eshwarappa")
fp=f1
fp.show()
s1=Son("Rajkumar", "Eshwarappa")
fp=s1
fp.show()

Father name: Eshwarappa
Son name: Rajkumar

Example-family1.cpp, Page no-622

class Father():
    __f_age=int
    def __init__(self, n):
        self.__f_age=n
    def GetAge(self):
        return self.__f_age
class Son(Father):
    __s_age=int
    def __init__(self, n, m):
        Father.__init__(self, n)
        self.__s_age=m
    def GetAge(self):
        return self.__s_age
    def son_func(self):
        print "son's own function"
basep=[Father]
basep=Father(45)
print "basep points to base object..."
print "Father's Age:",
print basep.GetAge()
del basep
basep=[Son(45, 20)]
print "basep points to derived object..."
print "Son's Age:",
print Father.GetAge(basep[0])
print "By typecasting, ((Son*) basep)..."
print "Son's age:",basep[0].GetAge()
del basep
son1=Son(45, 20)
derivedp=[son1]
print "accessing through derived class pointer..."
print "Son's Age:",
print derivedp[0].GetAge()

basep points to base object...
Father's Age: 45
basep points to derived object...
Son's Age: 45
By typecasting, ((Son*) basep)...
Son's age: 20
accessing through derived class pointer...
Son's Age: 20

Example-family2.cpp, Page no-626

class Father():
    __f_age=int
    def __init__(self, n):
        self.__f_age=n
    def GetAge(self):
        return self.__f_age
class Son(Father):
    __s_age=int
    def __init__(self, n, m):
        Father.__init__(self, n)
        self.__s_age=m
    def GetAge(self):
        return self.__s_age
basep=[Father]
basep=Father(45)
print "Father's Age:",
print basep.GetAge()
del basep
basep=[Son(45, 20)]
print "Son's Age:",
print basep[0].GetAge()
del basep

Father's Age: 45
Son's Age: 20

Example-draw.cpp, Page no-629

class graphics:
    def draw(self):
        print "point"
class line(graphics):
    def draw(self):
        print "line"
class triangle(graphics):
    def draw(self):
        print "triangle"
class rectangle(graphics):
    def draw(self):
        print "rectangle"
class circle(graphics):
    def draw(self):
        print "circle"
point_obj=graphics()
line_obj=line()
tri_obj=triangle()
rect_obj=rectangle()
circle_obj=circle()
basep=[]
basep.append(point_obj)
basep.append(line_obj)
basep.append(tri_obj)
basep.append(rect_obj)
basep.append(circle_obj)
print "Following figures are drawn with basep[i]->draw()..."
for i in range(5):
    basep[i].draw()

Following figures are drawn with basep[i]->draw()...
point
line
triangle
rectangle
circle

Example-pure.cpp, Page no-632

class AbsPerson:
    def Service1(self, n):
        self.Service2(n)
    def Service2(self, n): #pure virtual function
        pass
class Person(AbsPerson):
    def Service2(self, n):
        print "The number of years of service:", 58-n
Father=Person()
Son=Person()
Father.Service1(50)
Son.Service2(20)

The number of years of service: 8
The number of years of service: 38

Example-number.cpp, Page no-633

class number:
    __num=int
    def getdata(self):
        self.__num=int(raw_input("Enter an integer number: "))
    def show(self): #pure virtual function
        pass
class octnum(number):
    def show(self):
        print "Octal equivalent of", self._number__num,"=",oct(self._number__num)
class hexnum(number):
    def show(self):
        print "Hexadecimal equivalent of", self._number__num,"=",hex(self._number__num)
o1=octnum()
h1=hexnum()
o1.getdata()
o1.show()
h1.getdata()
h1.show()

Enter an integer number: 11
Octal equivalent of 11 = 013
Enter an integer number: 11
Hexadecimal equivalent of 11 = 0xb

Example-family3.cpp, Page no-637

class Father():
    __f_name=str
    def __init__(self, fname):
        self.__f_name=fname
    def __del__(self):
        del self.__f_name
        print "~Father() is invoked"
    def show(self):
        print "Father's name:", self.__f_name
class Son(Father):
    __s_name=str
    def __init__(self, sname, fname):
        Father.__init__(self, fname)
        self.__s_name=sname
    def __del__(self):
        del self.__s_name
        print "~Son() is invoked"
        Father.__del__(self)
    def show(self):
        print "Father's name:", self._Father__f_name
        print "Son's name:", self.__s_name
basep=[Father]
basep=Father("Eshwarappa")
print "basep points to base object..."
basep.show()
del basep
basep=Son("Rajkumar", "Eshwarappa")
print "basep points to derived object..."
basep.show()
del basep

basep points to base object...
Father's name: Eshwarappa
~Father() is invoked
basep points to derived object...
Father's name: Eshwarappa
Son's name: Rajkumar
~Son() is invoked
~Father() is invoked

Example-vptrsize.cpp, Page no-640

from ctypes import Structure, c_int, sizeof
class nonvirtual(Structure):
    _fields_=[('x', c_int)]
    def func(self):
        pass
class withvirtual(Structure):
    _fields_=[('x', c_int)]
    def func(self):
        pass
print "sizeof( nonvirtual ) =",sizeof(nonvirtual())
print "sizeof( withvirtual ) =",sizeof(withvirtual())

sizeof( nonvirtual ) = 4
sizeof( withvirtual ) = 4

Example-shapes.cpp, Page no-640

class description:
    __information=str
    def __init__(self, info):
        self.__information=info
    def show(self):
        print self.__information,
class sphere(description):
    __radius=float
    def __init__(self, info, rad):
        description.__init__(self, info)
        self.__radius=rad
    def show(self):
        print self._description__information,
        print "Radius = %g" %self.__radius
class cube(description):
    __edge_length=float
    def __init__(self, info, edg_len):
        description.__init__(self, info)
        self.__edge_length=edg_len
    def show(self):
        print self._description__information,
        print "Edge Length = %g" %self.__edge_length
small_ball=sphere("mine", 1.0)
beach_ball=sphere("plane", 24.0)
plan_toid=sphere("moon", 1e24)
crystal=cube("carbon", 1e-24)
ice=cube("party", 1.0)
box=cube("card borad", 16.0)
shapes=[]
shapes.append(small_ball)
shapes.append(beach_ball)
shapes.append(plan_toid)
shapes.append(crystal)
shapes.append(ice)
shapes.append(box)
small_ball.show()
beach_ball.show()
plan_toid.show()
crystal.show()
ice.show()
box.show()
print "Dynamic Invocation of show()..."
for i in range(len(shapes)):
    shapes[i].show()

mine Radius = 1
plane Radius = 24
moon Radius = 1e+24
carbon Edge Length = 1e-24
party Edge Length = 1
card borad Edge Length = 16
Dynamic Invocation of show()...
mine Radius = 1
plane Radius = 24
moon Radius = 1e+24
carbon Edge Length = 1e-24
party Edge Length = 1
card borad Edge Length = 16

Example, Page no-643

class shape:
    __val1=float
    __val2=float
    def getdata(self, a, b):
        self.__val1=a
        self.__val2=b
    def display_area(self):
        pass
class triangle(shape):
    def display_area(self):
        print "Area of trianle =", 0.5*self._shape__val1*self._shape__val2
class rectangle(shape):
    def display_area(self):
        print "Area of rectanle =", self._shape__val1*self._shape__val2
sptr=[shape]
sptr=triangle()
sptr.getdata(4.5, 2.2)
sptr.display_area()
sptr=rectangle()
sptr.getdata(4.5, 2.2)
sptr.display_area()

Area of trianle = 4.95
Area of rectanle = 9.9