C++ object-oriented programming 020: MyString inherited from string ---- (Peking University Mooc) (with comments)

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Original title

#include <cstdlib>
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
class MyString:public string
{
    
    
// 在此处补充你的代码
};


int main()
{
    
    
	MyString s1("abcd-"),s2,s3("efgh-"),s4(s1);
	MyString SArray[4] = {
    
    "big","me","about","take"};
	cout << "1. " << s1 << s2 << s3<< s4<< endl;
	s4 = s3;
	s3 = s1 + s3;
	cout << "2. " << s1 << endl;
	cout << "3. " << s2 << endl;
	cout << "4. " << s3 << endl;
	cout << "5. " << s4 << endl;
	cout << "6. " << s1[2] << endl;
	s2 = s1;
	s1 = "ijkl-";
	s1[2] = 'A' ;
	cout << "7. " << s2 << endl;
	cout << "8. " << s1 << endl;
	s1 += "mnop";
	cout << "9. " << s1 << endl;
	s4 = "qrst-" + s2;
	cout << "10. " << s4 << endl;
	s1 = s2 + s4 + " uvw " + "xyz";
	cout << "11. " << s1 << endl;
        sort(SArray,SArray+4);
	for( int i = 0;i < 4;i ++ )
	cout << SArray[i] << endl;
	//s1的从下标0开始长度为4的子串
	cout << s1(0,4) << endl;
	//s1的从下标5开始长度为10的子串
	cout << s1(5,10) << endl;
	return 0;
}

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prompt

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Code

public:
    MyString():string(){
    
    }
    MyString(const char* s):string(s){
    
    } //给基类成员赋值
    MyString(const MyString& a):string(a){
    
    } //派生类给基类成员赋值
    MyString(const string& a):string(a){
    
    } /*对于+号 那些 基类含+号函数 默认对基类的字符串相加 之后的出来的值 再用类型转换函数
                                          将 相加所返回的字符串再做类型转换函数 转换为MYString类型*/
    friend ostream & operator<<(ostream& os,const string& a) //用派生类实参 输出基类成员
    {
    
    
        os<<a;
        return os;
    }

    MyString operator()(int start,int length)
    {
    
    
        MyString ret(substr(start,length));
        return ret;
    }