zoukankan      html  css  js  c++  java
  • Effective C++ 笔记 —— Item 5: Know what functions C++ silently writes and calls

    For an enpty class, if you don't declare them yourself, compilers will declare their own versions of a copy constructor, a copy assignment operator, and a destructor. Furthermore, if you declare no constructors at all, compilers will also declare a default constructor for you.

    These functions are generated only if they are needed.

    Note that the generated destructor is non-virtual unless it's for a class inheriting from a base class that itself declares a virtual destructor (in which case the function's virtualness comes from the base class).

    If you want to support copy assignment in a class containing a reference member, you must define the copy assignment operator yourself.

    Compilers behave similarly for classes containing const members (such as objectValue in the modified class above). It's not legal to modify const members, so compilers are unsure how to treat them during an implicitly generated assignment function.

    Finally, compilers reject implicit copy assignment operators in derived classes that inherit from base classes declaring the copy assignment operator private.

    template<typename T>
    class NamedObject {
    public:
        // this ctor no longer takes a const name, because nameValue
        // is now a reference-to-non-const string. The char* constructor
        // is gone, because we must have a string to refer to.
        NamedObject(std::string& name, const T& value);
        //... // as above, assume no
        // operator= is declared
    private:
        std::string& nameValue; // this is now a reference
        const T objectValue; // this is now const
    };
    
    //Now consider what should happen here :
    std::string newDog("Persephone");
    std::string oldDog("Satch");
    
    NamedObject<int> p(newDog, 2); // when I originally wrote this, our dog Persephone was about to have her second birthday
    
    NamedObject<int> s(oldDog, 36); // the family dog Satch (from my childhood) would be 36 if she were still alive
    
    p = s; // what should happen to the data members in p?
  • 相关阅读:
    腾讯2016年实习生笔试题-蛇形数组-循环枚举遍历
    直接插入排序的加强版
    scanner 在java中的输入
    一种排序
    将string str中的str转换成字符数组
    呜呜呜
    ansible-playbook 实战案例 全网备份 实时备份
    Rsync服务实战
    TCP三次握手与四次握手
    centos 6.9修改系统默认字符集
  • 原文地址:https://www.cnblogs.com/zoneofmine/p/14921810.html
Copyright © 2011-2022 走看看