C++专题(三)

16.使用this指针复制数据.

头文件:

#include <iostream>

using namespace std;

class Obj
{
    int a, b;

public:
    Obj(int x = 0, int y = 0)
    {
        a = x;
        b = y;
    }

    void copy(Obj &);
    void display()
    {
        cout << "a = " << a << ", b = " << b << endl;
    }
};

void Obj::copy(Obj &aObj)
{
    if (this == &aObj)
        return;
    this->a = aObj.a;
    this->b = aObj.b;
}

源文件:

#include "obj.h"

void main(void)
{
    Obj x1(22, 25), x2(33, 46);

    cout << "x1: ";
    x1.display();
    cout << "x2: ";
    x2.display();
    x1.copy(x2);
    cout << "x1: ";
    x1.display();
}

结果:

x1: a = 22, b = 25

x2: a = 33, b = 46

x1: a = 33, b = 46

Mark:

　　当一个对象调用成员函数时,系统先将该对象的地址赋给this指针,然后调用成员函数,成员函数对成员数据进行操作时,隐含使用了this指针.

17.完整实现str类的例子.

头文件:

#ifndef _STR_H
#define _STR_H

#include <iostream>
#include <cstring>

using namespace std;

class str
{
private:
    char *st;

public:
    str(char *s);
    str(str &s);
    str & operator = (str &a);
    str & operator = (char *s);
    void print()
    {
        cout << st << endl;
    }

    ~str()
    {
        delete st;
    }
};

str::str(char *s)
{
    st = new char[strlen(s) + 1];
    strcpy(st, s);
}

str::str(str &a)
{
    st = new char[strlen(a.st) + 1];
    strcpy(st, a.st);
}

str & str::operator = (str &a)
{
    if (this == &a)
        return *this;
    delete st;
    st = new char[strlen(a.st) + 1];
    strcpy(st, a.st);
    return *this;
}

str & str::operator = (char *s)
{
    delete st;
    st = new char[strlen(s) + 1];
    strcpy(st, s);
    return *this;
}

#endif

源文件:

#include "str.h"

void main(void)
{
    str s1("We"), s2("They"), s3(s1);

    s1.print();
    s2.print();
    s3.print();

    s2 = s1 = s3;
    s3 = "Go home!";
    s3 = s3;
    s1.print();
    s2.print();
    s3.print();
}

结果:

We

They

We

We

We

Go home!

18.求4个数的最大值的类模板程序.

头文件:

#ifndef _MAX4_H
#define _MAX4_H

#include <iostream>

using namespace std;

template <class T>
class Max4
{
    T a, b, c, d;
    T Max(T a, T b)
    {
        return (a > b) ? a : b;
    }

public:
    Max4(T, T, T, T);
    T Max(void);
};

template <class T>
Max4<T>::Max4(T x1, T x2, T x3, T x4):a(x1),b(x2),c(x3),d(x4) 
{
}

template <class T>
T Max4<T>::Max(void)
{
    return Max(Max(a, b), Max(c, d));
}

#endif

源文件:

#include "max4.h"

void main(void)
{
    Max4<char> C('W', 'w', 'a', 'A');
    Max4<int> A(-25, -67, -66, -256);
    Max4<double> B(1.25, 4.3, -8.6, 3.5);
    cout << C.Max() << " " << A.Max() << " " << B.Max() << endl;
}

结果:

w -25 4.3

19.演示对4个数字求和的类模板程序.

头文件:

#ifndef _SUM_H
#define _SUM_H

template <class T, int size = 4>
class Sum
{
private:
    T m[size];

public:
    Sum(T a, T b, T c, T d)
    {
        m[0] = a;
        m[1] = b;
        m[2] = c;
        m[3] = d;
    }

    T S()
    {
        return m[0] + m[1] + m[2] + m[3];
    }
};

#endif

源文件:

#include <iostream>
#include "sum.h"

using namespace std;

void main(void)
{
    Sum<int, 4> num1(-23, 5, 8, -2);
    Sum<float, 4> f1(3.5f, -8.5f, 8.8f, 9.7f);
    Sum<double, 4> d1(355.4, 253.8, 456.7, -67.8);
    Sum<char, 4> c1('W', -2, -1, -1);            //字符减,等效于'W','U','T','S'
    cout << num1.S() << ", " << f1.S() << ", " << d1.S() << ", " << c1.S() << endl;
}

结果:

-12, 13.5, 998.1, S

20.使用缺省内联函数实现单一继承

头文件:

#include <iostream>

using namespace std;

class Point
{
private:
    int X, Y;

public:
    Point(int a, int b)
    {
        X = a;
        Y = b;
        cout << "Point..." << endl;
    }

    void Showxy()
    {
        cout << "X = " << X << ", Y = " << Y << endl;
    }

    ~Point()
    {
        cout << "Delete Point" << endl;
    }
};

class Rectangle:public Point
{
private:
    int H, W;

public:
    Rectangle(int a, int b, int h, int w):Point(a, b)
    {
        H = h;
        W = w;
        cout << "Rectangle..." << endl;
    }

    void Show()
    {
        cout << "H = " << H << ", W = " << W << endl;
    }

    ~Rectangle()
    {
        cout << "Delete Rectangle" << endl;
    }
};

源文件:

#include "rectangle.h"

void main(void)
{
    Rectangle r1(3, 4, 5, 6);
    r1.Showxy();
    r1.Show();
}

结果:

Point...

Rectangle...

X = 3, Y = 4

H = 5, W = 6

Delete Rectangle

Delete Point

Mark:

　　当定义派生类的一个对象时,首先调用基类的构造函数,对基类成员进行初始化,然后执行派生类的构造函数,如果某个基类仍是一个派生类,则这个过程递归进行.