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);  //復制第一個字符串
  strcpy(m_data, other.m_data);  //復制第二個字符串
  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;
}