CS31 Discussion 1E Spring 17: week 10 TA: Bo-Jhang Ho - PowerPoint PPT Presentation

CS31 Discussion 1E Spring 17’: week 10 TA: Bo-Jhang Ho bojhang@cs.ucla.edu Credit to former TA Chelsea Ju

What is “new” } Dynamically allocate memory } Step 1: allocate memory } Step 2: return the memory address } Don ’ t forget to return the memory } delete operator } Don’t lose the pointer, otherwise you will never be able to recycle the allocated memory!

Stack / heap

Stack / heap Local variables go here! Dynamic memory allocations go here!

Local variable v.s. dynamic allocation } Local variables are easier to manage } The last showing up variable is going recycled first } Dynamic memory allocation } A more flexible way to get available memory! } There is no way to determine when an allocated memory piece is going to be freed. Developers need to explicitly say which memory have to be recycled. } Memory fragmentation problem

An array of pointers } Scorpion* objects[10];

Accessing member operator } Dot (.) operator } Scorpion scor; scor.m_row = 3; } Arrow (->) operator } Scorpion *ptr = new Scorpion; ptr->m_row = 3; } Just treat dot (.) and arrow (->) operator as ‘s

Constructor / destructor } Constructor is for class (structure) initialization } Destructor gives the victim a chance to say good bye to the main program before it gets recycled } Usually we don’t need to override the default destructor, but if you dynamically allocate memory in constructor, this is the only chance you can free the allocated memory.

Constructor / destructor class Pit { public: Scorpion *sa; Scorpion *sb; int thirdVal; Pit() { sa = new Scorpion; sb = new Scorpion; thirdVal = 10; } ~Pit() { delete sa; delete sb; } };

Constructor / destructor class Pit { public: Scorpion *sa; Scorpion *sb; int thirdVal; Pit(); ~Pit(); }; Pit::Pit() { sa = new Scorpion; sb = new Scorpion; thirdVal = 10; } ~Pit::Pit() { delete sa; delete sb; }

Toward object-oriented } Treat things as objects, capture interaction of objects } Consider variables in a class as states } Usually variables are declared as private } Which means beyond the scope of the class, nobody can arbitrarily change the state } Consider methods as ways to change states } To enforce users to change states in a certain ways } Maintain the states, keep them valid } A method is a function in a class

What is this } this is a built-in keyword } this can only be used in a method } this means the owner of the method } this is a pointer } Why do we need to have the keyword this ? } Distinguish local variable from instance variable } Pass myself to others

What is this class Test { public: int score; Test(); saveScore(); }; Test::Test() { score = 60; } Test::saveScore(int score) { score = score; }

What is this class Test { public: int score; Test(); saveScore(); }; Test::Test() { score = 60; } Test::saveScore(int score) { this->score = score; }

What is this Player::Player(Pit* pp, int r, int c) { ... m_pit = pp; ... } bool Pit::addPlayer(int r, int c) { ... // Dynamically allocate a new Player and add it to the pit m_player = new Player(this, r, c); return true; }