string类实现（C++）

 class CMyString
 {
         friend std::ostream& operator<<( std::ostream& os, const CMyString& str);
         private:
                 char* m_pData; //  私有变量保存字符串
         public:
                 CMyString( const char* str = NULL ); // 构造函数
                 CMyString( const CMyString& str ); // 拷贝构造函数
                 ~CMyString( void ); // 析构函数
                 CMyString& operator=( const CMyString& str ); // 赋值运算符
                 CMyString operator+( const CMyString& str ); // 字符串连接
                 bool operator==( const CMyString& str ); // 判断相等
                 char operator[]( int idx ); // 数组索引
                 int getLength(); // 返回长度
 };

 CMyString::CMyString( const char* str )
 {
         if ( !str )
         {
                 this->m_pData = ;
         }
         else
         {
                 this->m_pData = new char[ strlen( str ) +  ];
                 strcpy( this->m_pData, str );
         }
 }

 CMyString::CMyString( const CMyString& str )
 {
         if ( !str.m_pData )
         {
                 this->m_pData = ;
         }
         else
         {
                 this->m_pData = new char[ strlen( str.m_pData ) +  ];
                 strcpy( this->m_pData, str.m_pData );
         }
 }

 CMyString::~CMyString( void )
 {
         if ( this->m_pData)
         {
                 delete[] this->m_pData;
                 this->m_pData = ;
         }
 }

 CMyString& CMyString::operator=( const CMyString& str)
 {
         if ( this != &str )
         {
                 delete[] this->m_pData;
                 if ( !str.m_pData )
                 {
                         this->m_pData = ;
                 }
                 else
                 {
                         this->m_pData = new char[ strlen( str.m_pData ) +  ];
                         strcpy( this->m_pData, str.m_pData );
                 }
         }
         return *this;
 }

 CMyString CMyString::operator+( const CMyString& str )
 {
         CMyString newString;
         if ( !str.m_pData )
         {
                 newString = *this;
         }
         else if ( !this->m_pData )
         {
                 newString = str;
         }
         else
         {
                 newString.m_pData = new char[ strlen( this->m_pData ) + strlen( str.m_pData ) +  ];
                 strcpy( newString.m_pData, this->m_pData );
                 strcat( newString.m_pData, str.m_pData );
         }

         return newString;

 }

 bool CMyString::operator==( const CMyString& str )
 {
         if ( strlen(this->m_pData) != strlen( str.m_pData ) )
         {
                 return false;
         }
         else
         {
                 return strcmp( this->m_pData, str.m_pData ) ? false : true;
         }
 }

 char CMyString::operator[]( int idx)
 {
         if ( idx >  && idx < strlen( this->m_pData ) )
         return this->m_pData[idx];
 }

 int CMyString::getLength()
 {
         return strlen(this->m_pData);
 }

 std::ostream& operator<<( std::ostream& os, const CMyString& str )
 {
         os<< str.m_pData;
         return os;
 }