C++ Mini-Course Part 1: Mechanics Part 2: Basics Part 3: References Part 4: Const Part 5: Inheritance Part 6: Libraries Part 7: Conclusion C Rulez! C++ - презентация

1 C++ Mini-Course Part 1: Mechanics Part 2: Basics Part 3: References Part 4: Const Part 5: Inheritance Part 6: Libraries Part 7: Conclusion C Rulez! C++ Rulez!

2 C++ Mini-Course Part 1: Mechanics

3 C++ is a superset of C New Features include –Classes (Object Oriented) –Templates (Standard Template Library) –Operator Overloading –Slightly cleaner memory operations

4 Some C++ code #ifndef __SEGMENT_HEADER__ #define __SEGMENT_HEADER__ class Point; class Segment { public: Segment(); virtual ~Segment(); private: Point *m_p0, *m_p1; }; #endif // __SEGMENT_HEADER__ Segment.h #include Segment.h #include Point.h Segment::Segment() { m_p0 = new Point(0, 0); m_p1 = new Point(1, 1); } Segment::~Segment() { delete m_p0; delete m_p1; } Segment.cpp

5 #include Segment.h #include Insert header file at this point. Use library header.

6 Header Guards #ifndef __SEGMENT_HEADER__ #define __SEGMENT_HEADER__ // contents of Segment.h //... #endif To ensure it is safe to include a file more than once.

7 Header Guards #ifndef __SEGMENT_HEADER__ #define __SEGMENT_HEADER__ // contents of segment.H //... #endif To ensure it is safe to include a file more than once. If this variable is not defined… Define it. End of guarded area.

8 Circular Includes Whats wrong with this picture? How do we fix it? #include controller.h // define gui //... gui.h #include gui.h class Controller { //... private: Gui* myGui; //... }; controller.h

9 Forward Declarations In header files, only include what you must. If only pointers to a class are used, use forward declarations. //Forward Declaration class Controller; // define gui //... gui.h //Forward declaration class Gui; class Controller { //... private: Gui* myGui; //... }; controller.h

10 Compilation Preprocessor Inlines #includes etc. Compiler Translates to machine code Associates calls with functions Linker Associates functions with definitions Object files Executable External Libraries, libc.so, libcs123.so

11 OK, OK. How do I run my Program? > make And if all goes well… >./myprog

12 C++ Mini-Course Part 2: Basics

13 What is a pointer? int x = 10; int *p; p = &x; p gets the address of x in memory. p x10

14 What is a pointer? int x = 10; int *p; p = &x; *p = 20; *p is the value at the address p. p x20

15 What is a pointer? int x = 10; int *p = NULL; p = &x; *p = 20; Declares a pointer to an integer & is address operator gets address of x * dereference operator gets value at p

16 Allocating memory using new Point *p = new Point(5, 5); new can be thought of a function with slightly strange syntax new allocates space to hold the object. new calls the objects constructor. new returns a pointer to that object.

17 Deallocating memory using delete // allocate memory Point *p = new Point(5, 5);... // free the memory delete p; For every call to new, there must be exactly one call to delete.

18 Using new with arrays int x = 10; int* nums1 = new int[10]; // ok int* nums2 = new int[x]; // ok Initializes an array of 10 integers on the heap. C++ equivalent of the following C code int* nums = (int*)malloc(x * sizeof(int));

19 Using new with multidimensional arrays int x = 3, y = 4; int** nums3 = new int[x][4];// ok int** nums4 = new int[x][y];// BAD! Initializes a multidimensional array Only the first dimension can be a variable. The rest must be constants. Use single dimension arrays to fake multidimensional ones

20 Using delete on arrays // allocate memory int* nums1 = new int[10]; int* nums3 = new int[x][4][5];... // free the memory delete[] nums1; delete[] nums3; Have to use delete[].

21 Destructors delete calls the objects destructor. delete frees space occupied by the object. A destructor cleans up after the object. Releases resources such as memory.

22 Destructors – an Example class Segment { public: Segment(); virtual ~Segment(); private: Point *m_p0, *m_p1; };

23 Destructors – an Example Segment::Segment() { m_p0 = new Point(0, 0); m_p1 = new Point(1, 1); } Segment::~Segment() { if (m_p0) delete m_p0; if (m_p1) delete m_p1; }

24 New vs Malloc MallocNew Standard C FunctionOperator (like ==, +=, etc.) Used sparingly in C++; used frequently in C Only in C++ Used for allocating chunks of memory of a given size without respect to what will be stored in that memory Used to allocate instances of classes / structs / arrays and will invoke an objects constructor Returns void* and requires explicit casting Returns the proper type Returns NULL when there is not enough memory Throws an exception when there is not enough memory Every malloc() should be matched with a free() Every new/new[] should be matched with a delete/delete[] Never mix new/delete with malloc/free

25 Classes vs Structs Default access specifier for classes is private; for structs it is public Except for this difference, structs are functionally the same as classes, but the two are typically used differently: structs should be thought of as lightweight classes that contain mostly data and possibly convenience methods to manipulate that data and are hardly ever used polymorphically struct Point { int x; int y; // convenience constructor Point(int a, int b) : x(a), y(b) { } distance to another point double distance(const Point &pnt) { int dx = m_x – pnt.x; int dy = m_y – pnt.y; return math.sqrt(dx*dx + dy*dy); } }; class Segment { public: Segment(); virtual ~Segment(); void setPoints(int x0, int y0, int x1, int y1); protected: Point *m_p0, *m_p1; }; void Segment::setPoints(int x0, int y0, int x1, int y1) { m_p0 = new Point(x0, y0); m_p1 = new Point(x1, y1); }

26 Syntactic Sugar -> Point *p = new Point(5, 5); // Access a member function: (*p).move(10, 10); // Or more simply: p->move(10, 10);

27 Stack vs. Heap On the Heap / Dynamic allocation On the Stack / Automatic allocation drawStuff() { Point *p = new Point(); p->move(10,10); //... } drawStuff() { Point p(); p.move(5,5); //... } What happens when p goes out of scope?

28 Summary with Header File begin header guard #ifndef __SEGMENT_HEADER__ #define __SEGMENT_HEADER__ class Point; class Segment { public: Segment(); virtual ~Segment(); protected: Point *m_p0, *m_p1; }; #endif // __SEGMENT_HEADER__ Segment.h header file forward declaration class declaration constructor destructor end header guard member variables need semi-colon

29 C++ Mini-Course Part 3: References

30 Passing by value void Math::square(int i) { i = i*i; } int main() { int i = 5; Math::square(i); cout << i << endl; }

31 Passing by reference void Math::square(int &i) { i = i*i; } int main() { int i = 5; Math::square(i); cout << i << endl; }

32 What is a reference? An alias – another name for an object. int x = 5; int &y = x; // y is a // reference to x y = 10; What happened to x? What happened to y?

33 What is a reference? An alias – another name for an object. int x = 5; int &y = x; // y is a // reference to x y = 10; What happened to x? What happened to y? – y is x.

34 Why are they useful? Unless you know what you are doing, do not pass objects by value; either use a pointer or a reference. Some people find it easier to deal with references rather then pointers, but in the end there is really only a syntactic difference (neither of them pass by value). Can be used to return more than one value (pass multiple parameters by reference)

35 How are references different from Pointers? Reference Pointer int &a; int *a; int a = 10; int b = 20; int &c = a; c = b; int a = 10; int b = 20; int *c = &a; c = &b;

36 C++ Mini-Course Part 4: const

37 Introducing: const void Math::printSquare(const int &i){ i = i*i; cout << i << endl; } int main() { int i = 5; Math::printSquare(i); Math::printCube(i); } Wont compile.

38 Can also pass pointers to const void Math::printSquare(const int *pi) { *pi = (*pi) * (*pi); cout << pi << endl; } int main() { int i = 5; Math::printSquare(&i); Math::printCube(&i); } Still wont compile.

39 Declaring things const const River nile; const River* nilePc; River* const nileCp; const River* const nileCpc

40 Read pointer declarations right to left // A const River const River nile; // A pointer to a const River const River* nilePc; // A const pointer to a River River* const nileCp; // A const pointer to a const River const River* const nileCpc

41 Lets Try References River nile; const River &nileC = nile; // Will this work? River &nile1 = nileC;

42 How does const work here? void Math::printSquares(const int &j, int &k) { k = k*k; // Does this compile? cout << j*j <<, << k << endl; } int main() { int i = 5; Math::printSquares(i, i); }

43 Returning const references is OK class Point { public: const double &getX() const; const double &getY() const; void move(double dx, double dy); protected: double m_x, m_y; }; const double & Point::getX() const { return m_x; } Function wont change *this.

44 C++ Mini-Course Part 5: Inheritance

45 How does inheritance work? #include Segment.h class DottedSegment : public Segment { // DottedSegment declaration }; must include parent header file DottedSegment publicly inherits from Segment

46 virtual In Java every method invocation is dynamically bound, meaning for every method invocation the program checks if a sub-class has overridden the method. You can disable this (somewhat) by using the keyword final in Java In C++ you have to declare the method virtual if you want this functionality. (So, virtual is the same thing as not final) Just like you rarely say things are final in Java, you should rarely not say things are virtual in C++

47 pure virtual functions In Java, the abstract keyword means the function is undefined in the superclass. In C++, we use pure virtual functions: –virtual int mustRedfineMe(char *str) = 0; –This function must be implemented in a subclass.

48 Resolving functions In Java: // Overriding methods public void overloaded(){ println(woohoo); super.overloaded(); } //constructor public Subclass(){ super(); } In C++: // Overriding methods void Subclass::overloaded(){ cout<

49 virtual Basic advice: for now make every method virtual except the constructor Make you declare your destructors virtual; if you do not declare a destructor a non- virtual one will be defined for you Segment(); virtual ~Segment(); this is important

50 C++ Mini-Course Part 6: Libraries

51 Namespaces Namespaces are kind of like packages in Java Reduces naming conflicts Most standard C++ routines and classes and under the std namespace –Any standard C routines (malloc, printf, etc.) are defined in the global namespace because C doesnt have namespaces

52 using namespace #include... std::string question = How do I prevent RSI?; std::cout << question << std::endl; using namespace std; string answer = Type less.; cout << answer << endl; Bad practice to do in header files!

53 STL Standard Template Library Contains well-written, templated implementations of most data structures and algorithms –Templates are similar to generics in Java –Allows you to easily store anything without writing a container yourself Will give you the most hideous compile errors ever if you use them even slightly incorrectly!

54 STL example #include using namespace std; typedef vector PointVector; typedef PointVector::iterator PointVectorIter; PointVector v; v.push_back(Point(3, 5)); PointVectorIter iter; for(iter = v.begin(); iter != v.end(); ++iter){ Point &curPoint = *iter; }

55 C++ Mini-Course Part 7: Conclusion

56 Other Resources The Java To C++ tutorial on the website is probably your best source of information The big thick book by Stroustrop in the back of the Sun Lab is the ultimate C++ reference A CS 123 TA, or specifically your mentor TA if you have been assigned one

57 Question and Answer Session