（2）基于对象 —class without pointer members — Complex

相关知识点

class template (模板) 简介

constructor (ctor, 构造函数)

 

一个变量或对象的数值的设定有两阶段：

• 初始化（initialization），创建新对象的时候执行
• 赋值（assignments）, 对象已经存在，时间点晚一些，效率差一些（对象已经存在，空间已经存在）

 

构造函数初始化列表赋值： 初始化阶段

大括号函数体内赋值： 赋值阶段（非初始化阶段） 

 

所以对于class中的 object data member、const data member、reference data member 等必须放在初始化列表中。

 

 ctor (构造函数) 可以有很多個 – overloading (重载)

 constructor (ctor, 构造函数) 被放在 private （单例设计模式）

 参数传递  pass by value vs. pass by reference （引用）(to const)

返回值传递：return by value vs. return by reference (to const)

参数和返回值的传递尽量传引用   （是在可以的情况下）

friend（友元）函数：

打破了 C++ 的封装的大门，类的友元函数能直接拿到该类对象的私有数据，而其他的普通函数只能通过接口访问对象的私有数据。

相同class的各个 objects 互为 friends（友员）

class complex {...// 相同class的各个 objects 互为 friends（友员）int func(const complex &param) {return param.re + param.im; // 可直接访问 私有数据}private:double re, im;
};

reference（引用） ：

本质就是指针（指针常量，不允许被改变，即引用必须初始化，且一旦初始化完成后不可更改，不能再指向其它类型），但是形式很漂亮。

reference 的主要两个应用就是（出于效率考虑）：

• 参数传递
• 返回值传递

Q：参数传递，什么时候用引用传递？ 
A：传递引用的效率和传递指针的效率一样，所传递的是指针的大小（4字节或8字节），所以一般对于内建类型来说：by value 和 by reference 都可，效率相差不大；但是如果要传递结构体或object的话：尽量 by reference，而且，如果不改变所传递的reference，就在 reference前面加上 const。
Q：返回值传递，什么时候传递引用？ 
A：需要返回或传递出去的东西（object）已经存在空间，且其生命期在此函数之外，即函数执行完后，需要传递出去的东西还存在，那么就可以 return by reference。对于 local object，即其生命期只局限于在该函数执行期，函数执行完后，该 local object 也就死亡了，对于这样的东西，就不能 return by reference。传出者无需知道接收者是否以 reference 形式接收。 
Tips：传递参数和返回值传递的时候，首先考虑能否用 reference，能的话就尽量用引用来传递，另外在传递参数的时候，如果不修改传进来的引用，就最好加上 const。

 

operator overloading(操作符重载)

操作符可重载为以下两种函数：

• 成员函数 
  • 任何的 non-ststic 成员函数都有一个隐藏的 this 指针
• 非成员函数（global函数） 
  • << 只能重载为非成员函数（友元或非友元都可）

操作符重載-1, 成員函數（有this）

操作符重載-2, 非成員函數  (無 this)

temp obbject（临时对象）：typename(); 

临时对象没有名称，生命期到下一行就结束，标准库中应用的较多。

complex operator + (const complex &x, const complex &y) {return complex(x.real() + y.real(), x.imag() + y.imag()); // 临时对象
}

 

Complex

#ifndef __MYCOMPLEX__
#define __MYCOMPLEX__class complex; 
complex&__doapl (complex* ths, const complex& r);
complex&__doami (complex* ths, const complex& r);
complex&__doaml (complex* ths, const complex& r);class complex
{
public:complex (double r = 0, double i = 0): re (r), im (i) { }complex& operator += (const complex&);complex& operator -= (const complex&);complex& operator *= (const complex&);complex& operator /= (const complex&);double real () const { return re; }double imag () const { return im; }
private:double re, im;friend complex& __doapl (complex *, const complex&);friend complex& __doami (complex *, const complex&);friend complex& __doaml (complex *, const complex&);
};inline complex&
__doapl (complex* ths, const complex& r)
{ths->re += r.re;ths->im += r.im;return *ths;
}inline complex&
complex::operator += (const complex& r)
{return __doapl (this, r);
}inline complex&
__doami (complex* ths, const complex& r)
{ths->re -= r.re;ths->im -= r.im;return *ths;
}inline complex&
complex::operator -= (const complex& r)
{return __doami (this, r);
}inline complex&
__doaml (complex* ths, const complex& r)
{double f = ths->re * r.re - ths->im * r.im;ths->im = ths->re * r.im + ths->im * r.re;ths->re = f;return *ths;
}inline complex&
complex::operator *= (const complex& r)
{return __doaml (this, r);
}inline double
imag (const complex& x)
{return x.imag ();
}inline double
real (const complex& x)
{return x.real ();
}inline complex
operator + (const complex& x, const complex& y)
{return complex (real (x) + real (y), imag (x) + imag (y));
}inline complex
operator + (const complex& x, double y)
{return complex (real (x) + y, imag (x));
}inline complex
operator + (double x, const complex& y)
{return complex (x + real (y), imag (y));
}inline complex
operator - (const complex& x, const complex& y)
{return complex (real (x) - real (y), imag (x) - imag (y));
}inline complex
operator - (const complex& x, double y)
{return complex (real (x) - y, imag (x));
}inline complex
operator - (double x, const complex& y)
{return complex (x - real (y), - imag (y));
}inline complex
operator * (const complex& x, const complex& y)
{return complex (real (x) * real (y) - imag (x) * imag (y),real (x) * imag (y) + imag (x) * real (y));
}inline complex
operator * (const complex& x, double y)
{return complex (real (x) * y, imag (x) * y);
}inline complex
operator * (double x, const complex& y)
{return complex (x * real (y), x * imag (y));
}complex
operator / (const complex& x, double y)
{return complex (real (x) / y, imag (x) / y);
}inline complex
operator + (const complex& x)
{return x;
}inline complex
operator - (const complex& x)
{return complex (-real (x), -imag (x));
}inline bool
operator == (const complex& x, const complex& y)
{return real (x) == real (y) && imag (x) == imag (y);
}inline bool
operator == (const complex& x, double y)
{return real (x) == y && imag (x) == 0;
}inline bool
operator == (double x, const complex& y)
{return x == real (y) && imag (y) == 0;
}inline bool
operator != (const complex& x, const complex& y)
{return real (x) != real (y) || imag (x) != imag (y);
}inline bool
operator != (const complex& x, double y)
{return real (x) != y || imag (x) != 0;
}inline bool
operator != (double x, const complex& y)
{return x != real (y) || imag (y) != 0;
}#include <cmath>inline complex
polar (double r, double t)
{return complex (r * cos (t), r * sin (t));
}inline complex
conj (const complex& x) 
{return complex (real (x), -imag (x));
}inline double
norm (const complex& x)
{return real (x) * real (x) + imag (x) * imag (x);
}#endif   //__MYCOMPLEX__

 

 

#include <iostream>
#include "complex.h"using namespace std;ostream&
operator << (ostream& os, const complex& x)
{return os << '(' << real (x) << ',' << imag (x) << ')';
}int main()
{complex c1(2, 1);complex c2(4, 0);cout << c1 << endl;cout << c2 << endl;cout << c1+c2 << endl;cout << c1-c2 << endl;cout << c1*c2 << endl;cout << c1 / 2 << endl;cout << conj(c1) << endl;cout << norm(c1) << endl;cout << polar(10,4) << endl;cout << (c1 += c2) << endl;cout << (c1 == c2) << endl;cout << (c1 != c2) << endl;cout << +c2 << endl;cout << -c2 << endl;cout << (c2 - 2) << endl;cout << (5 + c2) << endl;return 0;
}