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[];
       m_data[]='\0';
      }
      else
      {
       m_data=new char[strlen(str)+];
       strcpy(m_data,str);
      }

 }
 Strings::Strings(const Strings &another)
 {
   m_data=new char[strlen(another.m_data)+];
   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)+];
   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 ;

 }