default constructor 是分为 trivial default constructor(平凡默认构造函数,即不进行任何构造动作)和 non trivial default constructor(非平凡默认构造函数) 什么情况下 default constructor 是 trivial 的呢?cppreference 中说明了这一点: 当下列各项全部为真时,类 T 的默认构造函数为平凡的(平凡默认构造函数是不进行任...
我們發現以上程式compile沒問題,執行也沒問題,唯一遺憾的是getI()的private int i是個亂數,因為synthesized default Constructor只會對class中的class Type加以初始化,對於built-in type則不會初始化,所以int i還是亂數,但string s因為是library type,非built-in type,所以已經初始化成空字串。這告訴我們,若data ...
三、对于defualt constructor,当一个class内显式地存在constructor(包括default constructor)时,编译器不会再生成它,但如果这个class满足以上4种情况至少一种时,编译器就需要负责执行相关的初始化:对于(1)要调用成员对象的default constructor;对于(2)要调用基类的default constructor;对于(3)要设定虚函数表的指针;对于(...
in the case of the subobject being a variant member, selects a non-trivial function. If no user-defined constructors are present and the implicitly-declared default constructor is not trivial, the user may still inhibit the automatic generation of an implicitly-defined default constructor by the...
Referencingcppreference.com, If no user-declared constructors of any kind are provided for a class type (struct, class, or union), the compiler will always declare a default constructor as an inline public member of its class. If some user-declared constructors are present, the user may sti...
Yes, a special member function can be default-defined out-of-line in a .cpp file. Realize that by doing so, some of the properties of an inline-defaulted function will not apply to your class. For example, if your copy constructor is default-defined out-of-line, your class will not ...
First, let us learn about the default constructor in C++. The default constructor is a special kind of constructor that has no arguments and is used to set default values to the data members of a class. Example: class demo{intage;intid;public:demo(){age=10;id=1;}}; ...
There are two additional cases in which a synthesized default constructor is needed: (1). The class either declares (or inherits) a virtual function (2). The class is derived from an inheritance chain in which one or more base classes are virtual ...
Edit & run on cpp.sh What the hell, then? Objects get default-constructed but primitives don't? Sep 4, 2009 at 9:23pm jsmith(5804) The default constructor for int does nothing. In the above, on line 5 you are not (even though it looks that way) default constructing a. ...
If a class type has a default constructor, both value initialization and default initialization will call the default constructor. Thus, for such a class such as the Foo class in the example above, the following are essentially equivalent: Foo foo{}; // value initialization, calls Foo() defau...