從一個例子看類的構造函數、析構函數、拷貝構造函數和賦值函數的實現

class String
{
public:
    //普通構造函數
    String(const char *str = NULL);
    //拷貝構造函數
    String(const String &other);
    //析構函數
    ~String(void);
    //賦值函數
    String &operator =(const String &other);
private:
    //用於保存字符串
    char *m_data;
};

String::String(const char *str)
{
    if(str == NULL)
    {
        m_data = new char[1];
        *m_data = '\0';
    }
    else
    {
        int length = strlen(str);
        m_data = new char[length + 1];
        strcpy(m_data, str);
    }
}

String::String(const String &other)
{
    int length = strlen(other.m_data);
    m_data = new char[length + 1];
    strcpy(m_data, other.m_data);
}

String & String::operator =(const String &other)
{
    if(this == &other)//檢查自賦值
        return *this;
    delete []m_data;//釋放原有內存資源
    //分配新的內存資源並複製內容
    int length = strlen(other.m_data);
    m_data = new char[length + 1];
    strcpy(m_data, other.m_data);
    //返回本對象的引用
    return *this;
}

String::~String(void)
{
    delete []m_data;
    //delete m_data;
}