Classes and Objects Instructor: 小黑

Files and StreamsFiles and Streamsin C++, we can do like this:in C :

Files and StreamsFiles and Streamsin C : in C++, we can do like this:

Files and StreamsFiles and Streams

http://www.cplusplus.com/

More IOstream library

function you can use:getgetlinereadungetread/writeseekg/seekpflush

Structures V.S. ClassesStructures V.S. Classes

The class is a foundation of OOP. It is very similar to the expanded structures that group related data and functions together.

C++ provides three ways of accessing class members：Public: can be accessed by members of its class as well as members of any other class and non-member functions, including main()Private: can only be accessed by other members of the same class. Protected: when dealing with inheritance

class Employee {

public:

Employee() {}

Employee(char *name) {}

~Employee() {}

char * getName() {}

...

private:

char _name[10];

int _salary;

float _height;

};

Classes and Objects Classes and Objects

Classes and Objects Classes and Objects

When an object of the class is declared, the constructor is automatically called.Employee em1; Employee em2(“John”);

class Employee {

public:

Employee() {}

Employee(char *name) {}

~Employee() {}

char * getName() {}

...

private:

char _name[10];

int _salary;

float _height;

};

Define methodsDefine methodsFollowing is a sample class:class XYZCoord { public: XYZCoord( int x, int y, int z) {

_x = x, _y=y, _z=z;

}

int getX() { return _x; }

void output() {

cout << “( ” << _x << “,” << _y << “,” << _z << “ )”<< endl;

}

private: int _x, _y, _z;};

The constructor is a simple and automatic way to initialize the objects.

int main() {

Employee myemployee;

myemployee.init();

return 0;

}

Purpose of ConstructorsPurpose of Constructors

class Employee {public:

void init() {...}...

private:char _name[10];int _salary;float _height;

};

Use of ConstructorsUse of Constructors

We can define a default constructor separately or by providing default arguments for all parameters.

class Employee {

public:

Employee();

Employee(char *name = “Blackie”, int salary = 100,

float height = 170.5);

…

private:

char _name[10];

int _salary;

float _height;

};

DestructorsDestructors

There can be only have one Destructor. Destructor has no parameter and no return type. It’s usually used to release resource.

class Player {public:

Player( ) {char *name = new

char[strlen(name)+1];strcpy ( _name,

name);}~Player() {

delete [] _name;}

private:char *_name;

}

Today’s practiceToday’s practice Define a class Pet

Data member: _name, _level; Default values of _name and _level are “Lucky” and 1,

respectively. User can pass name and level when constructing a Pet

object.

Define a class Player Data member: _name, _level, _pet; Default values of _name and _level are “player” and 1,

respectively. User can pass player’s name, player’s level, pet’s name

and pet’s level when constructing a Player object.

Create an input.txt file that as follow:

Each line contains four attributes: player’s name, player’s level, pet’s name, pet’s level.

Create an output.txt file that save your data before exit.

Today’s practice ( contd.)Today’s practice ( contd.)

Ann 50 Molly 46Tom 8 Max 7Sam 20 Rocky 13Ted 5 pepe 1

Today’s practice ( contd.)Today’s practice ( contd.)

Provide a simple UI as follow: 1. Add new player

Input player’s name. ( No need to input level, pet’s name and pet’s level )

2. Show all players Print all player’s name, level and their pet.

3. Save & Leave Save all information in output.txt file like input.txt’s

format.