侯捷老师的C++代码：基于对象的类别之二带指针的成员函数 Mystring实现

//makefile
cc = g++
prom = mystring
obj = mystring.o
$(prom):$(obj)
    rm -rf *.exe;
    $(cc) -o $(prom) $(obj)

//头文件
#ifndef __MYSTRING__
#define __MYSTRING__


class String{
    public:
        String(char* cstr = nullptr);
        String(const String& str);
        String& operator=(const String& str);
        ~String();
        char* get_c_str() const {return m_data;}
    private:
        char* m_data;
};

#include<iostream>
#include<cstring>
using namespace std;
inline String::String(char* cstr)
{
    if(cstr){
        m_data = new char[strlen(cstr) + 1];
        strcpy(m_data, cstr);
    }
    else{
        m_data = new char[1];
        *cstr = '';
    }

    
}

inline String::~String()
{
    delete[] m_data;
}


inline String::String(const String& str)
{
    m_data = new char[strlen(str.m_data) + 1];
    strcpy(m_data, str.m_data);
}

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


ostream& operator<<(ostream& os, const String& str)
{
    os << str.get_c_str();
    return os;
}

#endif

//定义文件
#include"mystring.h"

int main()
{
    String s1((char*)("Hello "));
    cout << s1 << endl;
    String s2(s1) ;
    cout << s2 << endl;
    String s3(s1);
    s3 = s2;
    cout << s3 << endl;
    return 0;
}