#include<iostream>
using namespace std;
class String
{
private:
    char * m_data;
public:
    String(char *data);
    ~String();
    String(const String& str);
    String& operator =(const String& str);
};
String::String(char *data)
{
    if(data==NULL)
    {
        m_data=new char;
        *m_data='\0';
    }
    else
    {
        int n=strlen(data);
        m_data=new char[n+1];
        strcpy(m_data,data);
    }
}
String::~String()
{
    delete []m_data;
}
String::String(const String &str)
{
    delete [] m_data;
    int n=strlen(str.m_data);
    m_data=new char[n+1];
    strcpy(m_data,str.m_data);
}
String& String::operator=(const String &str)
{
    if(&str==this)
    {
        return *this;
    }
    else
    {
        int n=strlen(str.m_data);
        delete []m_data;
        m_data=new char[n+1];
        strcpy(m_data,str.m_data);
        return *this;
    }
}
int main()
{
    char * a="hello world";
    string b=a;
    string c="hh";
    b=c;
}