class String{public:  String(const char* = nullptr); //普通構(gòu)造函數(shù)  String(const String& other);  //拷貝構(gòu)造函數(shù)  ~String(void); //析構(gòu)函數(shù)  String& operator = (const String& other);  //賦值函數(shù)  private:  char* m_data;}; //普通構(gòu)造函數(shù)String::String(const char* str){  if(str == nullptr){    m_data = new char[1];  //對空字符自動申請存放結(jié)束標(biāo)志'/0'的空    *m_data = '/0';  }else{    m_data = new char[strlen(str) + 1];  //+1是為了多余一個字符存放'/0'    strcpy(m_data, str);  }} //拷貝構(gòu)造函數(shù)String::String(const String& other){  if(other == nullptr){    m_data = nullptr;  }else{    //注意下面括號里面都是other.m_data    m_data = new char[strlen(other.m_data) + 1];    strcpy(m_data, other.m_data);  }} //析構(gòu)函數(shù)String::~String(void){  if(m_data != nullptr){    delete [] m_data;    m_data = nullptr;  }} //賦值運算符String& String::operator=(const String& other){  //判斷是否是給自己賦值  if(this != other){    delete [] m_data;  //先釋放掉原來的內(nèi)存    if(other == nullptr){      m_data = nullptr;    }else{       m_data = new char[strlen(other.m_data) + 1];      strcpy(m_data, other.m_data);    }  }  return *this;}

String& operator + (String& other){  char* tmp = m_data;  m_data = new char[strlen(m_data) + strlen(other.m_data) + 1];  strcpy(m_data, tmp);  //復(fù)制第一個字符串  strcpy(m_data, other.m_data);  //復(fù)制第二個字符串  delete [] tmp; //記得刪除這個內(nèi)存  return *this;} String& operator = (String& other){  if(this = other){    return *this;  }  if(m_data != nullptr){    delete [] m_data;  //先釋放之前的內(nèi)存  }  m_data = new char [strlen(other.m_data) + 1];  strcpy(m_data, other.m_data);  return *this;}