String类中构造函数、拷贝构造函数、赋值函数的实现

class String{public:String(const char *str = NULL);String(const String &rhs);String &operator=(const String &rhs);~String();private:char *m_str;}String::String(const char *str){if(str == NULL){m_str = new char[1];m_str[0] = '\0';}else{m_str = new char[strlen(str)+1];strcpy(m_str, str);}}String::String(const String &rhs){m_str = new char[strlen(rhs.m_str)+1];strcpy(m_str, rhs.m_str);}String &String::operator=(const String &rhs){if(this == &rhs)return *this;delete []m_str;m_str = new char[strlen(rhs.m_str)+1];strcpy(m_str, rhs.m_str);return *this;}String::~String(){delete []m_str;}