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IBM Research – Zurich
Process Management Technologies
C++ (3. Vorlesung)
Inheritance
Thomas Gschwind <[email protected]...>
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Agenda
Constants and Constant Expressions
Object Oriented Programming
–
–
–
–
–
–
–
2
Object Model
Code and Type Inheritance
Binding: Static vs Dynamic
Abstract Classes and Interfaces
Multiple Inheritance
Casts
Implementation
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C/C++ const vs Java final
C/C++ const specifies that a given variable or object a variable
points to is constant
Java final specifies that the value of a variable cannot be
changed
3
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C/C++ const vs Java final
C++
Java
const int a=17;
final int a=17;
vector<string> v1;
v1.push_back("Hello");
Vector v1=new Vector();
v1.add("Hello");
const vector<string> v2;
v2.push_back("Hello");
final Vector v2=new Vector();
v2.add("Hello");
const vector<string> *vp=&v2; final Vector vp=v2;
vp=&v1;
vp=v1;
Vp->bush_back("Hello");
vp.add("Hello");
vector<string> *const vq=&v2;
vq=&v1;
vq.bush_back("Hello");
vector<string> *vr=&v2;
4
Vector vr=v2;
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C/C++ const vs Java final
C++
Java
OK const int a=17;
final int a=17;
OK
OK vector<string> v1;
OK v1.push_back("Hello");
Vector v1=new Vector();
v1.add("Hello");
OK
OK
OK const vector<string> v2;
======================
v2.push_back("Hello");
OK int sz=v2.size();
final Vector v2=new Vector(); OK
v2.add("Hello");
OK
int sz=v2.size();
OK
OK const vector<string> *vp=&v2; final Vector vp=v2;
OK vp=&v1;
======
vp=v1;
======================
vp.bush_back("Hello");
vp.add("Hello");
OK
OK
============================
vector<string> *const vq=&v2;
======
vq=&v1;
OK vq.bush_back("Hello");
======================
vector<string> *vr=&v2;
5
Vector vr=v2;
Th. Gschwind. Fortgeschrittene Programmierung in C++.
OK
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C/C++ const (cont’d)
OK const vector<string> v2;
======================
v2.push_back("Hello");
OK int sz=v2.size();
v2.push_back is NOT OK
BUT v2.size is OK?
How can the compiler tell the difference?
The secret is the declaration of the member…
… class vector {
public:
void push_back(T elem);
int size() const;
}
6
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C++11: Constant Expressions
Certain initializers require a constant expression
– Arrays stored on the stack (e.g., char buf[256])
– Switch expressions (same in Java)
– Functions may not be used in such constant expressions
(again, same in Java)
C++11 allows to use functions in such expressions
– Must be marked as constexpr
– Must be possible to evaluate them at compile time
Useful in combination with static_assert
constexpr int min(int a, int b) { return a<b? a : b; }
int numbers[min(consta, constb)];
7
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
C++11: static_assert
Allows to assert that a given condition is met at compile time
Alternatives
– The assert statement is evaluated at run-time
(not desirable if condition can be evaluated at compile time)
– The #error directive by the C++ preprocessor
(cannot deal properly with template instatiations)
template<typename T, int N>
class Buffer {
static_assert(N>16, "Buffer size too small");
…
};
8
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Agenda
Constants and Constant Expressions
Object Oriented Programming
–
–
–
–
–
–
–
9
Object Model
Code and Type Inheritance
Binding: Static vs Dynamic
Abstract Classes and Interfaces
Multiple Inheritance
Casts
Implementation
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Inheritance
Definition of a class on the basis of another
Derived, sub, or child class
– Inherits the implementation of the base or parent class
– May add new methods
– May replace existing methods
Kinds of inheritance
– Code inheritance
– Interface inheritance
10
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Object Model: C++ vs. Java
Java
– Every object inherits from the class Object
– All objects are stored on the heap and accessed through pointers
– Primitive types (byte, int, long, float, double, etc) are not objects
C++
– There is no Object class (i.e., there is no common base class)
– Objects can be anywhere and passed using whatever mechanism
– Primitive types (byte, int, long, float, double, etc) are not objects
11
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Types of Inheritance
public
– To define an is-a relationship
– Public and protected members will be inherited as defined in the base
class
protected, private
– To define a has-a relationship (style-wise, frequently it is better to define
the base class as attribute in the derived class)
– Public and protected members become protected, respectively private,
members of the derived class
– Avoid this type of inheritance
12
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Code and Type Inheritance
–
–
–
–
find
toupper
tolower
…
String.h
Extend a string class with new functions
class String2: public String {
// type definition
public:
void tolower() {
int n=length();
for(int i=0;i<n;++i) {
(*this)[i]=tolower(*this[i]);
}
}
// …
}
13
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
“public” Derived Classes
They are polymorph
– They have the type of both the derived class
– They inherit the type of the base class(es)
=> May be used wherever the base class can be used
In the base context
– Only those attributes which are defined in the base class may be used
14
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Access
The derived class may access the public members of the
base class
No access to private members
Additionally, members may be declared protected
=> These members may be used by the class itself
=> These members may be used in derived classes
Essentially, this is the same as in Java except that package
does not exist
15
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
String2.h
String.h
String2
class String {
// type declaration+definition
protected:
char *strg; unsigned int len;
public:
…
}
Style! In this case I would not consider
this useful. Our previous
implementation is not slower almost
as readable and encapsulates the
// type definition
implementation of the string class.
class String2: public String {
public:
void tolower() {
for(int i=0;i<len;++i) { strg[i]=tolower(strg[i]); }
}
// …
}
16
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Type Compatibility (“public” Sub Classes)
type-comp-1.cc
void foo(String2 s2) {
s2.tolower();
cout << s2 << endl;
}
int main(int argc, char
String s1="Hello ";
String2 s2="World!";
String &s3=s2;
cout << s1[0];
cout << s2[0];
cout << s3[0];
foo(s1);
foo(s2);
foo(s3);
*argv[]) {
//
//
//
//
ok,
ok,
ok,
ok,
every String2 is a String
String implements operator[]
String2 inherits operator[]
String implements operator[]
// error s1 is a String
// ok, s2 is of type String2
// error, type of s3 is String
}
17
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Type Compatibility
(“private” & “protected” Sub Classes)
type-comp.cc
class parent { // … };
class priv_inh: private parent { // … public: void priv(…); };
class prot_inh: protected parent { // … public: void prot(); };
int main(int argc, char *argv[]) { Good for code-inheritance! Avoid!
parent p1(1,2);
If you need another class’s code,
priv_inh pri(1,2);
define it as attribute of your class
prot_inh pro(1,2);
(Aggregation).
parent &p2=pri;
parent &p3=pro;
// error, private base
// error, protected base
}
void priv_inh::priv(parent &p) {
priv_inh pri(1,2);
if(…) priv(pri);
// ok, inheritance visible to ourself
}
18
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Overriding Members
In C++, members of the base class can be overridden
Simply define the same member again in the sub class
Like in Java
19
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Inheritance – An Example
Stack_with_Count.cc
Stack.cc
class Stack {
int buf[256], sp;
20
public:
Stack() { sp=256; }
void push(int i) { s[--sp]=i; }
int pop() { return s[sp++]; }
int empty() { return sp==256; }
};
class Stack_with_Count: public Stack {
int cnt;
public:
Stack_with_Count() { cnt=0; }
void push(int i) { Stack::push(i); ++cnt; }
int pop() { --cnt; return Stack::pop(); }
int elements() { return cnt; } };
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Inheritance and Binding
This is extra
dangerous, we’ll
come back to it.
void fill1(Stack s) { s.push(1); s.push(2); }
void fill2(Stack &s) { s.push(1); s.push(2); }
test-Stack.cc
void fill3(Stack *s) { s->push(1); s->push(2); }
int main(int argc, char *argv[]) {
Stack s;
Stack_with_Count sc;
sc.push(2); sc.push(4);
fill1(s); fill1(sc);
cout << sc.elements() << endl;
fill2(s); fill2(sc);
cout << sc.elements() << endl;
fill3(&s); fill3(&sc);
cout << sc.elements() << endl; }
21
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Binding
Binding refers to the process of binding different entities to a
specific symbol
– For instance a value to a variable
– An implementation of a function to a function name
– …
22
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Static Binding
Member function to be executed is determined on the basis of
the variable’s static type
– Used in our current example
– Member may be inlined
– Faster code
In object-oriented programming frequently not desired
23
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Dynamic Binding
Member function to be executed is determined on the basis of the object’s
runtime type (“dynamic binding”)
Member functions where dynamic binding is to be used need to be declared
as virtual
– A member function declared virtual will stay virtual for all subclasses
– Style: repeat the virtual keyword in all the subclasses
Member function to be executed determined via virtual method table
– No inlining
– A bit slower (generally, don’t worry about this)
24
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Dynamic Binding (cont’d)
Stack.cc
class Stack {
int s[256], sp;
public:
Stack()
virtual
virtual
virtual
: sp(256) {}
void push(int i) { s[--sp]=i; }
int pop() { return s[sp++]; }
int empty() { return sp==256; }
Stack_with_Count.cc
};
25
class Stack_with_Count: public Stack {
int cnt; Not necessary to repeat virtual
here, but it’s a good style!
public:
Stack_with_Count() : cnt(0) {}
virtual void push(int i) { Stack::push(i); ++cnt; }
virtual int pop() { --cnt; return Stack::pop(); }
virtual int elements() { return cnt; } };
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Dynamic Binding: C++11 Features
override
A member function may be marked as override to signify it
overrides a non-final virtual member function of the base class
final
A member function or class may be marked final to indicate it
may not be overridden
class Stack_with_Count: public Stack {
...
virtual void push(int i) override;
}
class Stack final {
...
};
class Stack {
...
int empty() final { return sp==256; }
};
26
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Where are Virtual Members Useful?
Default implementations
Callbacks and hooks
In abstract classes or interfaces
Never implement a member that only returns an error
– Use abstract methods
27
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Dynamic Binding and Overriding Methods
In C++
Arguments are fixed
– void push(int x) cannot be replaced with
void push(long x) in the subclass.
Return value of a function can be restricted
– Stack Stack::clone() can be replaced with
Stack_wc Stack_wc::clone() in the subclass.
– Again it can be preferable to return a pointer or a reference to the
Stack/Stack_wc object
28
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
foo_client.cc
Callbacks and Hooks
class foo_client {
protected:
// callback
virtual foo *get_foo_from_cache(int i) { return NULL; }
// default implementation
virtual foo *get_foo_from_server(int i) { // … }
public:
virtual foo *get_foo(int i) {
foo *f=get_foo_from_cache(i);
if (f==NULL) f=get_foo_from_server(i);
return f;
}
// …
};
29
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Abstract Classes
Express a concept
Define an interface
Cannot be instantiated
Can use pointers and references to such classes
Examples
– Article data base
– A hash map that can store any data type
30
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Article Database – Class Hierarchy
ArticleDB
inherits
ArticleDBFactory
creates
LocalArticleDB
RemoteArticleDB
CachingRemoteArticleDB
31
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
ArticleDBFactory
class ArticleDBFactory {
Preferences p;
public:
ArticleDBFactory(const char *config_file) {
// …
}
ArticleDB *getArticleDB(const char *group) {
// determine the database to be used for
// group
if (caching_enabled)
return new CachingRemoteArticleDB(…);
else
return new RemoteArticleDB(…);
}
}
32
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Article Database
class ArticleDB {
public:
virtual Article *getArticle(int nbr)=0;
virtual void postArticle(int nbr, Article *a)=0;
};
=0 after the member indicates that it is abstract
If one or methods are abstract, the entire class is abstract
Abstract classes cannot be instantiated
A method without state and all members being virtual defines a
pure virtual class and is equivalent to a Java interface
33
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
RemoteArticleDB
class RemoteArticleDB: public ArticleDB {
string h; int p; // …
public:
RemoteArticleDB(const char *host, int port)
: h(host), p(port) { // … }
virtual Article getArticle(int nbr) {
Article a;
// connect to server, if not already connected
// retrieve article
return a;
}
// …
~RemoteArticleDB() { // close connection, if still open }
};
34
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
CachingRemoteArticleDB
class CachingRemoteArticleDB: public RemoteArticleDB {
string h; int p; // …
Map<int,Article> cache;
public:
RemoteArticleDB(const char *host, int port)
: h(host), p(port) { // … }
virtual Article getArticle(int nbr) {
Article a;
try { a=cache.get(nbr) }
catch (NotFoundException) {
cache[nbr]=a=RemoteArticleDB::getArticle(nbr);
}
return a;
}
// …
35
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Using the Article Database
int main(int argc, char *argv[]) {
ArticleDBFactory f("…/.config");
const char *grp;
while(grp=getselectionfromuser()) {
ArticleDB *db=f.getArticleDB(grp);
// interact with database db
// …
delete db;
//
//
//
//
only calls the destructor of
class ArticleDB!
the connection to our server won’t
be closed
}
}
36
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Solution
Define a virtual destructor in the base class
virtual ~ArticleDB() {}
Now the virtual destructor is called and the derived class has a
chance to free its resources
Hint: As soon as you have a virtual
member function, implement a
virtual destructor
37
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Virtual or not Virtual?
If possible/useful, define an interface
– In C++ a pure virtual class defines an interface
– C++ does not need special interface
C++ has multiple inheritance
Not Virtual
– If not useful to derive a class from your class
– Performance *is* important (unlikely)
38
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Multiple Inheritance: Interfaces
Unlike Java, C++ does not provide an interface concept
Multiple inheritance provides the same functionality
Multiple inheritance is more powerful
C++ provides multiple inheritance
struct Car {
struct Player {
virtual void draw() = 0;
}
virtual void play() = 0;
}
class CarPlayer: public Car, public Player {
// …
}
39
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Multiple Inheritance: Name Collisions
Two base classes/interfaces provide the “same” function
– Members have different semantics, needs to be looked at individually
– Interfaces and same semantics of the members, no problem
– Classes with implementation, resolve explicitly
Let’s assume, both Car and Player provide each a to_string()
member function, each with an implementation
class CarPlayer: public Car, public Player {
string to_string() {
return "("+Car::to_string()+","+
Player::to_string()+")";
}
}
40
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Multiple Inheritance: “Diamond Shape” Inheritance
If Base has no state, there is no problem
class Base;
class A: public Base;
class B: public Base;
class Child: public A, public B;
If Base has a state, this becomes tricky (generally, avoid)
– Shall Base be inherited twice: no change necessary to the above
– Shall Base be shared among the sub-classes: inherit virtually
• class A: public virtual Base;
class B: public virtual Base;
41
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Casts
Casts allow to “convert” an object of type FOO into a different
type BAR.
static_cast<T>(o)
reinterpret_cast<T>(o)
dynamic_cast<T>(o)
const_cast<T>(o)
(T)o
42
/* C-Cast */
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
static_cast<T>(o)
Converts an Object o into a given type T
Is statically verified (i.e., during compile time)
Pre-defined conversion
User-defined conversion
Example
fraction fr(1,2);
double f=static_cast<double>(fr);
43
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
reinterpret_cast<T>(o)
The value (bit-pattern) of object o will be
interpreted to be of type T
Not verified
Example
char *mem=reinterpret_cast<char*>
malloc(n*sizeof(char));
44
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
dynamic_cast<T>(o)
Checks whether o is of type T (down/crosscast)
Dynamically verified (i.e., during run-time)
Uses Run Time Type Information (RTTI, generated for classes
with a virtual method)
Returns NULL if o is not of type T
Example
child c(…), *c1;
parent *p=&c;
c1=dynamic_cast<child*>p;
45
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Squares and Rectangles
I had a colleague who was unsure whether to derive rectangle
from square or vice-versa. What would you recommend to
him?
Implement a set of sample programs illustrating various options
and your recommendation!
The programs should demonstrate why your solution is better
than the other solutions
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Squares and Rectangles
Shape
inherits
Line
Circle
Triangle
…
Class hierarchy for a vector graphics program
We have an abstract class Shape from which various geometric
shapes are being derived
Task: Add the following classes: Square, Rectangle
47
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Slicing
void fill1(Stack s) { s.push(1); s.push(2); }
void fill2(Stack &s) { s.push(1); s.push(2); }
test-Stack.cc
void fill3(Stack *s) { s->push(1); s->push(2); }
int main(int argc, char *argv[]) {
Stack s;
Stack_with_Count sc;
sc.push(2); sc.push(4);
fill1(s); fill1(sc);
cout << sc.elements() << endl;
The stack will be passed by
value. In order to be able to
do this, it will be “sliced”.
fill2(s); fill2(sc);
cout << sc.elements() << endl;
fill3(&s); fill3(&sc);
cout << sc.elements() << endl; }
48
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Slicing (cont’d)
That is the problem with the fill1(Stack s) function
Using this signature, fill1 allocates enough memory to store
an object of type Stack
Stack_wc uses more memory than Stack!
If Stack_wc is not implemented nicely we may get an
inconsistent object (if the attributes of Stack are not kept in
accordance with the guidelines of Stack)
49
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Dynamic Binding – Implementation
How is dynamic binding implemented?
How do we know which member function to execute?
50
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Stack_wc.cc
Stack.cc
Virtual Method Table
51
class Stack {
virtual void push(int i);
virtual int pop();
virtual int empty();
};
class Stack_wc
: public Stack {
virtual void push(int i);
virtual int pop();
};
vmtab
push
pop
empty
vmtab
push
Adressraum
Stack::push
Stack::pop
Stack::empty
Stack_wc::push
pop
empty
Th. Gschwind. Fortgeschrittene Programmierung in C++.
Stack_wc::pop
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Summary
Constants and Constant Expressions
Object Oriented Programming
–
–
–
–
–
–
–
52
Object Model
Code and Type Inheritance
Binding: Static vs Dynamic
Abstract Classes and Interfaces
Multiple Inheritance
Casts
Implementation
Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Exercise 1
In what order are constructors and destructors being executed
when an object is constructed or destructed respectively.
Show the same in case of multiple inheritance.
In case of multiple inheritance, what we can do in order to avoid
the inheritance of multiple copies from the base class (diamond
inheritance relationship).
Justify your answer with a correct program.
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Exercise 2 – Connect 4 with Inheritance
Implement a simple version of “Vier Gewinnt”
– You have a playing field of 7 columns by 6 rows.
– Player 1 and player 2 in turns type in the column where to throw in their
stone in
– Gravity pulls the stone towards the lowest row
After each turn display the field using ASCII art.
Once a player has 4 of his stones in a row (horizontal, vertical,
diagonal), he has won
Try to implement the game in a modular way as we will extend it
in future classes
Interfaces to be used, to be published
54
© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Exercise 3 – Connect 4 with Inheritance (1st Extension)
Implement a computer player
The computer first checks whether the player can get 4 in a row
and if so tries to stop the player from winning
If the player cannot win in the next turn, the computer throws in
his stone into a random column
You are free to improve your computer player per your liking
Interface to be used, to be published
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© 2014 IBM Corporation
IBM Research – Zurich
Process Management Technologies
Next Lecture
Liskov Substitution Principle
Templates
Have fun solving the examples!
See you next week!
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Th. Gschwind. Fortgeschrittene Programmierung in C++.
© 2014 IBM Corporation
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