string类的基本函数编写

class String
   {
   public:
        String(const char *str=NULL);
        String(const String &otherdata);
        ~String(void);
         String &operator=(const String &otherdata);
         outputString();
   private:
         char *input_data;
   };
   String::~String()
  {
  delete[]input_data;//destructor析构函数，释放地址空间
  }
   String::(const String &otherdata)
   {
   assert(str!=NULL);
   if(str==NULL)
   {
   inputdata=new char[1];
   *inputdata='\0';
   }
   else
   {
   int length=strlen(otherdata.inputdata);
   inputdata=new char[length];
   strcpy(inputdata,otherdata.inputdata);
     }
 }
  String::(const)