String 类的函数实现

#include<iostream>
//#include<string>
using namespace std;

class Strings
{
public:
    Strings(const char * str=NULL);
    
    Strings(const Strings &another);
    ~Strings();
    Strings & operator=(const Strings &ths);
private:
    char *m_data;
};
Strings::Strings(const char *str)
{
     if(str==NULL)
     {
      m_data=new char[1];
      m_data[0]='\0';
     }
     else
     {
      m_data=new char[strlen(str)+1];
      strcpy(m_data,str);
     }

}
Strings::Strings(const Strings &another)
{
  m_data=new char[strlen(another.m_data)+1];
  strcpy(m_data,another.m_data );
}
Strings::~Strings()
{
delete [] m_data;
}

Strings &Strings::operator=(const Strings &ths)
{
  if(this==&ths)
      return *this;
  delete[]m_data;
  m_data=new char[strlen(ths.m_data)+1];
  strcpy(m_data,ths.m_data);
  return *this;
}
int main()
{
  Strings a("abcdefg");
  printf("%s\n",a);
  Strings b(a);
  printf("%s\n",b);
  Strings c=b;
  printf("%s\n",c);
  system("pause");
  return 0;

}