c++面试题string类的具体实现

#include<iostream>
//#include<ostream>
//class ostream;
class string
{
public:
    //constructor
    string(const char* str=nullptr);
    //copy constructor
    string(const string&);
    //assign operator
    string& operator=(const string& rhs);
    //deconstructor
    ~string();
    
    friend std::ostream& operator<<(std::ostream & os, string &str);    //友元函数可以访问私有成员
private:
    char* m_data;
};
//构造函数的实现
string::string(const char* str)
{
    std::cout << "构造函数被调用\n";
    if (nullptr == str) {
        m_data = new char[1];
        m_data[0] = '\0';
    }
    else
    {
        m_data = new char[strlen(str) + 1];
        strcpy(m_data, str);
    }
}
//拷贝构造函数的实现
string::string(const string& another) {
    std::cout << "拷贝构造函数被调用：\n";
    m_data = new char[strlen(another.m_data) + 1];
    strcpy(m_data, another.m_data);
}
// 赋值运算
string& string::operator=(const string& rhs) {
    std::cout << "赋值运算符被调用：\n";
    if (this == &rhs) return *this;
    delete[]m_data;
    m_data = new char[strlen(rhs.m_data) + 1];
    strcpy(m_data, rhs.m_data);
    return *this;
}
string::~string()
{
    std::cout << "析构函数被调用：\n";
    delete[]m_data;
    m_data = nullptr;
}
std::ostream& operator<<(std::ostream & os, string& str) {
    os << str.m_data;
    return os;
}
int main() {
    string str1("jibisheng");
    string str2("zhangjie");
    string str3(str1);
    string str4;
    str4 = str3;
    std::cout << str1 << "\n"<<str2<<std::endl<<str3<<std::endl<<str4<<std::endl;
    return 0;    
}