抽象
封装和数据隐藏
多态
继承
代码复用
以上是面向对象编程很重要的特点，class可以集合上述特征，class简单来说是关于user定义类型的抽象，包括数据表示和数据操作两大内容
定义一个class需要两部分
首先是class声明，数据成员用于描述数据构成，还有方法，或者说成员函数，公开接口
其次是class方法定义，说明成员函数怎么用
一般将声明放在头文件中，将方法放在源文件中
方法和数据分开就是数据隐藏
把实现细节放在一起并和公用接口分开就是封装
listing10_1_to_10_3_stock // listing 10.1 stock00.h -- Stock class interface // version 00 #ifndef STOCK00_H_ #define STOCK00_H_ #includeclass Stock // class declaration { private: std::string company; long shares; double share_val; double total_val; void set_tot() { total_val = shares * share_val; } public: void acquire(const std::string & co, long n, double pr); void buy(long num, double price); void sell(long num, double price); void update(double price); void show(); }; // note semicolon at the end #endif // listing 10.2 stock00.cpp -- implementing the Stock class // version 00 #include #include "stock00.h" void Stock::acquire(const std::string & co, long n, double pr) { company = co; if (n < 0) { std::cout << "Number of shares can't be negative; " << company << " shares set to 0.n"; shares = 0; } else shares = n; share_val = pr; set_tot(); } void Stock::buy(long num, double price) { if (num < 0) { std::cout << "Number of shares purchased can't be negative. Transaction is aborted.n"; } else { shares += num; share_val = price; set_tot(); } } void Stock::sell(long num, double price) { using std::cout; if (num < 0) { cout << "Number of shares sold can't be negative. Transaction is aborted.n"; } else if (num > shares) { cout << "You can’t sell more than you have! Transaction is aborted.n"; } else { shares -= num; share_val = price; set_tot(); } } void Stock::update(double price) { share_val = price; set_tot(); } void Stock::show() { std::cout << "Company: " << company << " Shares: " << shares << 'n' << " Share Price: $" << share_val << " Total Worth: $" << total_val << 'n'; } // listing 10.3 usestck0.cpp -- the client program // compile with stock00.cpp #include #include "stock00.h" int main() { Stock fluffy_the_cat; fluffy_the_cat.acquire("NanoSmart", 20, 12.50); fluffy_the_cat.show(); fluffy_the_cat.buy(15, 18.125); fluffy_the_cat.show(); fluffy_the_cat.sell(400, 20.00); fluffy_the_cat.show(); fluffy_the_cat.buy(300000, 40.125); fluffy_the_cat.show(); fluffy_the_cat.sell(300000, 0.125); fluffy_the_cat.show(); return 0; }
一般用m_前缀或者_后缀来为类成员命名
// listing10_4_to_10_6_stock // lisitng 10.4 stock10.h -- Stock class declaration with constructors, destructor added #ifndef STOCK10_H_ #define STOCK01_H_ #includeclass Stock { private: std::string company; long shares; double share_val; double total_val; void set_tot() { total_val = shares * share_val; } public: // two constructors Stock(); // default constructor Stock(const std::string & co, long n = 0, double pr = 0.0); ~Stock(); // noisy destructor void buy(long num, double price); void sell(long num, double price); void update(double price); void show(); }; #endif // listing 10.5 stock10.cpp -- Stock class with constructors, destructor added #include #include "stock10.h" // constructors (verbose versions) Stock::Stock() // default constructor { std::cout << "Default constructor calledn"; company = "no name"; shares = 0; share_val = 0.0; total_val = 0.0; } Stock::Stock(const std::string & co, long n, double pr) { std::cout << "Constructor using " << co << " calledn"; company = co; if (n < 0) { std::cout << "Number of shares can't be negative; " << company << " shares set to 0.n"; shares = 0; } else shares = n; share_val = pr; set_tot(); } // class destructor Stock::~Stock() // verbose class destructor { std::cout << "Bye, " << company << "!n"; } // other methods void Stock::buy(long num, double price) { if (num < 0) { std::cout << "Number of shares purchased can't be negative. " << "Transaction is aborted.n"; } else { shares += num; share_val = price; set_tot(); } } void Stock::sell(long num, double price) { using std::cout; if (num < 0) { cout << "Number of shares sold can't be negative. Transaction is aborted.n"; } else if (num > shares) { cout << "You can't sell more than you have! Transaction is aborted.n"; } else { shares -= num; share_val = price; set_tot(); } } void Stock::update(double price) { share_val = price; set_tot(); } void Stock::show() { using std::cout; using std::ios_base; // set format to #.### ios_base::fmtflags orig = cout.setf(ios_base::fixed, ios_base::floatfield); std::streamsize prec = cout.precision(3); cout << "Company: " << company << " Shares: " << shares << 'n'; cout << " Share Price: $" << share_val; // set format to #.## cout.precision(2); cout << " Total Worth: $" << total_val << 'n'; // restore original format cout.setf(orig, ios_base::floatfield); cout.precision(prec); } // listing 10.6 usestok1.cpp -- using the Stock class // compile with stock10.cpp #include #include "stock10.h" int main() { { using std::cout; cout << "Using constructors to create new objectsn"; Stock stock1("NanoSmart", 12, 20.0); // syntax 1 stock1.show(); Stock stock2 = Stock("Boffo Objects", 2, 2.0); // syntax 2 stock2.show(); cout << "Assigning stock1 to stock2:n"; stock2 = stock1; cout << "Listing stock1 and stock2:n"; stock1.show(); stock2.show(); cout << "Using a constructor to reset an objectn"; stock1 = Stock("Nifty Foods", 10, 50.0); // temp object cout << "Revised stock1:n"; stock1.show(); cout << "Donen"; } return 0; }
// listing10_7_to_10_9_stock // listing 10.7 stock20.h -- augmented version #ifndef STOCK20_H_ #define STOCK20_H_ #includeclass Stock { private: std::string company; int shares; double share_val; double total_val; void set_tot() { total_val = shares * share_val; } public: Stock(); // default constructor Stock(const std::string & co, long n = 0, double pr = 0.0); ~Stock(); // do-nothing destructor void buy(long num, double price); void sell(long num, double price); void update(double price); void show()const; const Stock & topval(const Stock & s) const; }; #endif // listing 10.8 stock20.cpp -- augmented version #include #include "stock20.h" // constructors Stock::Stock() // default constructor { company = "no name"; shares = 0; share_val = 0.0; total_val = 0.0; } Stock::Stock(const std::string & co, long n, double pr) { company = co; if (n < 0) { std::cout << "Number of shares can't be negative; "<< company << " shares set to 0.n"; shares = 0; } else shares = n; share_val = pr; set_tot(); } // class destructor Stock::~Stock() // quiet class destructor {} // other methods void Stock::buy(long num, double price) { if (num < 0) { std::cout << "Number of shares purchased can't be negative. Transaction is aborted.n"; } else { shares += num; share_val = price; set_tot(); } } void Stock::sell(long num, double price) { using std::cout; if (num < 0) { cout << "Number of shares sold can’t be negative. Transaction is aborted.n"; } else if (num > shares) { cout << "You can’t sell more than you have! Transaction is aborted.n"; } else { shares -= num; share_val = price; set_tot(); } } void Stock::update(double price) { share_val = price; set_tot(); } void Stock::show() const { using std::cout; using std::ios_base; // set format to #.### ios_base::fmtflags orig = cout.setf(ios_base::fixed, ios_base::floatfield); std::streamsize prec = cout.precision(3); cout << "Company: " << company << " Shares: " << shares << 'n'; cout << " Share Price: $" << share_val; // set format to #.## cout.precision(2); cout << " Total Worth: $" << total_val << 'n'; // restore original format cout.setf(orig, ios_base::floatfield); cout.precision(prec); } const Stock & Stock::topval(const Stock & s) const { if (s.total_val > total_val) return s; else return *this; } // listing 10.9 usestok2.cpp -- using the Stock class // compile with stock20.cpp #include #include "stock20.h" const int STKS = 4; int main() { // create an array of initialized objects Stock stocks[STKS] = { Stock("NanoSmart", 12, 20.0), Stock("Boffo Objects", 200, 2.0), Stock("Monolithic Obelisks", 130, 3.25), Stock("Fleep Enterprises", 60, 6.5) }; std::cout << "Stock holdings:n"; int st; for (st = 0; st < STKS; st++) stocks[st].show(); // set pointer to first element const Stock * top = &stocks[0]; for (st = 1; st < STKS; st++) top = &top->topval(stocks[st]); // now top points to the most valuable holding std::cout << "nMost valuable holding:n"; top->show(); return 0; }
// listing10_10_to_10_12_stack
// listing 10.10 stack.h -- class definition for the stack ADT
#ifndef STACK_H_
#define STACK_H_
typedef unsigned long Item;
class Stack
{
private:
enum { MAX = 10 }; // constant specific to class
Item items[MAX]; // holds stack items
int top; // index for top stack item
public:
Stack();
bool isempty() const;
bool isfull() const;
// push() returns false if stack already is full, true otherwise
bool push(const Item & item); // add item to stack
// pop() returns false if stack already is empty, true otherwise
bool pop(Item & item); // pop top into item
};
#endif
// listing 10.11 stack.cpp -- Stack member functions
#include "stack.h"
Stack::Stack() // create an empty stack
{
top = 0;
}
bool Stack::isempty() const
{
return top == 0;
}
bool Stack::isfull() const
{
return top == MAX;
}
bool Stack::push(const Item & item)
{
if (top < MAX)
{
items[top++] = item;
return true;
}
else
return false;
}
bool Stack::pop(Item & item)
{
if (top > 0)
{
item = items[--top];
return true;
}
else
return false;
}
// stacker.cpp -- testing the Stack class
#include
#include // or ctype.h
#include "stack.h"
int main()
{
using namespace std;
Stack st; // create an empty stack
char ch;
unsigned long po;
std::cout << "Please enter A to add a purchase order,n P to process a PO, or Q to quit.n";
while (cin >> ch && toupper(ch) != 'Q')
{
while (cin.get() != 'n')
continue;
if (!isalpha(ch))
{
std::cout << 'a';
continue;
}
switch (ch)
{
case 'A':
case 'a': std::cout << "Enter a PO number to add: ";
cin >> po;
if (st.isfull())
std::cout << "stack already fulln";
else
st.push(po);
break;
case 'P':
case 'p': if (st.isempty())
std::cout << "stack already emptyn";
else
{
st.pop(po);
std::cout << "PO #" << po << " poppedn";
}
break;
}
std::cout << "Please enter A to add a purchase order,n P to process a PO, or Q to quit.n";
}
std::cout << "Byen";
return 0;
}
