FAQ about C + + constructors

[1] What is a constructor used for?

Constructors construct objects of classes, initialize class variables, allocate resources (memory, files, semaphores, socket interfaces, and so on)

[2] list x; and list x (); What's the difference ?

The previous one is an object that defines the list, and the latter is a function that returns a list value

[3] is it possible for a class constructor to invoke another constructor to initialize itself?

To give an example of this problem:

class Foo {public:  foo (char  x);  Foo (charint  y);  ...}; Foo::foo (char  x) {  ...   0);  // This line does does help initialize the this object!!   ...}

Statement:

Just initializes a temporary object, not the This object, so the statement does not have the desired effect.

[4] Whether the default function function of the Fred class must be fred::fred ()?

Not necessarily, the default constructor refers to a constructor without parameters, for example: a::a (int x = 3, int y = 5)

Therefore, a class can not have a default constructor , which is important to note!

[5] If you want to create an Fred pair like an array, what number of constructor functions will be called?

For Fred a[10]; or Fred *a = new Fred (); If the class Fred has a default constructor, the default constructor is called 10 times, and if the class Fred does not have a default constructor, the compilation error occurs;

For Fred A[10] = {fred (5,7)}; The Fred (int, int) constructor is called;

[6] When a constructor initializes a member variable, should it use an "initialization list" or "assignment"?

initialization list;

Advantages: 1) Improve performance; 2)

[7] Is there a problem with the this pointer in the constructor?

[8] What is a "name constructor" (Named Constructor Idiom)?

[9] "value back" means an extra copy?

[10] Why can't we initialize a static member variable in the constructor initialization list?

[11] Why would a class with a static member variable have a link error?

[12] What is "static initialization order Fiasco"?

[13] should I avoid "static initialization order Fiasco"?

[14] Why construct-on-first-use static variables instead of pointers?

[15] How can I avoid "static initialization order fiasco" in statically members?

[16] Do I have to worry about the built-in type of "static initialization order Fiasco"?

[17] What if something goes wrong with the constructor?

[18] What is a "named parameter idiom" (Named Parameter Idiom)?

[19] Why do I get an error by declaring a Foo object with foo x (Bar ()) ?

FAQ about C + + constructors