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//string???????????????????????????//??????String::String(const char *str) {    if (str == NULL) {        //???????????????'\0'???        m_data = new char[1];        *m_data = '\0';    } else {        int length = strlen(str);        m_data = new char[length + 1];        //??? NULL ?????        if (m_data == nullptr) {            cout << "out of space!";            //???????????        }    }}//??????String::String(const String &other) {    //???????    m_data = new char(other.length() + 1);    memcpy(m_data, other.m_data, other.length());    m_data[other.length()] = '\0';}//????String::~String() {    //?????????    delete[] m_data;}//???????String &String::operator=(const String &other) {    //???????????????????    if (this == &other) {        return *this;    }    //?????????    delete[] m_data;    //?????????    m_data = new char(other.length() + 1);    memcpy(m_data, other.m_data, other.length());    m_data[other.length()] = '\0';    return *this;}

//?????//1. ?????????????????????????????//2. ???????????????//3. ????????????????//4. ???new?delete??????????????//5. ??????memcpy???????????//6. ????????????????unique_ptr???RAII??

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