程序代码：

#pragma once
#ifndef STRING0_H_
#define STRING0_H_
#include<iostream>

class String {
private:
    char *str;//存储数据
    int len;  //记录数据长度
    static int num_strings;  //静态成员变量，计算类对象的数量
     static const int CINLIM = 80; //静态常量  重载输入函数时用来做char数组的常量
public:
    String();  //默认构造函数
    String(const char *c);  //用字符串常量初始化的构造函数
    ~String();   //析构函数
    String(const String &s);   //复制构造函数
    int length() { return len; }//返回长度
    String& operator=(const String &s);//重载运算符=，提高效率
    String& operator=(const char *c);  //重载运算符=，提高效率，不需要临时创建和删除对象
    friend std::ostream& operator<<(std::ostream &os,const String &s);//输出函数
    friend std::istream& operator>>(std::istream &is, String &s);//输入函数
    bool operator<(const String &s)const {
        return(std::strcmp(str, s.str) < 0);
    }//比较函数，推荐用  friend bool operator<(const String &s1,const String &2){return (std::strcmp(s1.str,s2.str)<0);} 代替
    bool operator>(const String &s)const {
        return(std::strcmp(str, s.str) > 0);
    }//比较函数
    friend bool operator==(const String &s1, const String &s2)
    {
        return (std::strcmp(s1.str, s2.str) == 0);
    }//比较函数，可以用友元函数来实现
    char & operator[](int i);//如数组一样访问字符的函数，对非const对象使用
    const char& operator[](int i)const;//如数组一样访问字符串的函数，对const对象使用

    static int howmany();//静态成员函数，无法使用对象来调用，只能用类与作用域解析运算式来调用，如 int count = String::howmany();




};
#endif // !STRING0_H_

程序代码：

#include "stdafx.h"
#include"String0.h"
#include<cstring>
#include<cstdlib>
using std::cout;

int String::num_strings = 0;

String::String() {
    len = 4;
    str = new char[4];
    strcpy_s(str,4, "C++");//strcpy函数不在这里定义，所以需要std作用域，char* strcpy(char*,const char*);
    num_strings++;
    cout << num_strings << ":\"" << str << "\"default object created\n";
}
String::String(const char* c){
    len = std::strlen(c);
    str = new char[len + 1];
    strcpy_s(str,len+1, c);
    num_strings++;
    cout << num_strings << ":\"" << str << "\"default object created\n";
}
String::String(const String &s) {
    len = s.len;
    str = new char[len + 1];
    strcpy_s(str,len+1, s.str);
    num_strings++;
    cout << num_strings << ":\"" << str << "\"default object created\n";
}
String::~String() {
    cout << "\"" << str << "\"object deleted,";
    num_strings--;
    cout << num_strings << "left\n";
    delete[] str;
}
String& String::operator=(const String &s) {
    if (this == &s)
        return *this;
    else {
        delete[]str;//这一步必不可少，必须先释放里面的内存，在为其分配足够的内存
        len = s.len;
        str = new char[len + 1];
        strcpy_s(str,len+1,s.str);
        num_strings++;
        cout << num_strings << ":\"" << str << "\"default object created\n";
    }
    return *this;
}
String& String::operator=(const char* c) {
    delete[]str;
    len = std::strlen(c);
    str = new char[len + 1];
    strcpy_s(str, len + 1, str);
    num_strings++;
    cout << num_strings << ":\"" << str << "\"default object created\n";

    return *this;
}
std::ostream& operator<<(std::ostream & os, const String &s) {
    os << s.str;
    return os;
}
std::istream& operator>>(std::istream & is, String &s) {
    char temp[String::CINLIM];
    is.get(temp, String::CINLIM);
    if (is) {
        s = temp;//重载赋值函数实现
    }
    while (is&&is.get() != '\n')continue;
    return is;
}
char& String::operator[](int i) {
    return str[i];
}
const char& String::operator[](int i)const {
    return str[i];
}

int String::howmany()
{
    return num_strings;
}
// TODO: 在 STDAFX.H 中引用任何所需的附加头文件，
//而不是在此文件中引用

程序代码：

// String(类和动态内存分配笔记）.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>
#include"String0.h"
const int NUM = 10;
using namespace std;

int main()
{
    String name;
    cout << "Hi,what's your name?\n>>";
    cin >> name;//输入姓名，就是到这一步就跳出了这个窗口
    cout << "Misty Gutz,please enter up to 10 short sayings <empty line to quit>:";
    
    char*temp=NULL;
    int i = 1;
    String *sayings[NUM];//创建一个指针数组
    while(cin>>temp){
        sayings[i] = new String(temp);
        cout << String::howmany()<< ":" << *sayings[i];
    }

    cout << "Here are your sayings:";
    for (int i = 0; i < String::howmany(); i++) {
        cout << sayings[i][0] << ":" << *sayings[i] << endl;
    }
    String first = *sayings[0];
    String Short;
    int j,k=0;
    for (j = 1; j <String::howmany(); j++) {
        if (sayings[j]->length() < sayings[j - 1]->length())
            k = j;
    }//求最短的String对象
    
    cout << "Shortest saying:";
    cout << *sayings[j];
    cout << "First alphabetically:" << endl;
    cout << first[0];

    cout << "This program used " << String::howmany() << "String objects.Bye";
    return 0;
}

程序代码：

String& String::operator=(const char* c) {
    delete[]str;
    len = std::strlen(c);
    str = new char[len + 1];
    strcpy_s(str, len + 1, str);//该句有错，应该为strcpy_s(str, len + 1, c);
    num_strings++;
    cout << num_strings << ":\"" << str << "\"default object created\n";

    return *this;
}