面试 - 实现string

class string{public:string(const char *str=NULL);string(const string &other);~string(void);string& operator=(const string &other);private:char *m_data;};string::string(const char *str){if (str==NULL){m_data = new char[1];*m_data = '\0';}else{int len = strlen(str);m_data = new char[len+1];strcpy(m_data,str);}}string::string(const string &other){int len = strlen(other.m_data);m_data = new char[len+1];strcpy(m_data,other.m_data);}string::~string(void){delete [] m_data;}string& string::operator=(const string& other){if (this==&other){return *this;}else{delete [] m_data;int len = strlen(other.m_data);m_data = new char[len+1];strcpy(m_data,other.m_data);}return *this;}