"C + +" various member variables

From: Huang Bongyong Handsome

Const Constant Object:

The object is declared as a constant, that is, const hyong m, a const object cannot invoke a function that might alter the value of an object, so a const object can only invoke the constants constant function in the class , because a function that is not const can change the value of an object.

A const object can invoke a public member of a class, such as M.A, if it is public.

The public member of a const object cannot be re-assigned, as M.a=3 is wrong. However, you can reassign a public static member variable in a class because the static member is not part of the constant object, and he belongs to the entire class.

Object array:

An array of objects, each member of an array, is an object, such as Hyong A[3], where a[0],a[1],a[2] is an object of the Hyong type.

Initializes the object array, and if there is a default constructor the statement Hyong A[3] will invoke the default constructor to initialize 3 objects;

If the object array has a constructor with a parameter, you can initialize Hyong a[3]={1,2,3} like this.

If the object array has constructors with multiple parameters, the initialization method is Hyong A[3]={hyong, Hyong (3,4), Hyong (4,5)}.

Object members in the class:

That is, the object is a member of another class. such as class B{public:a X;}

If you want to initialize X with a constructor with parameters, you must initialize it with an initialization list .

Example:

#include <iostream>using namespacestd;classa{ Public:    intA, B; A () {a= B =0; cout<<"A Default constructor"<<Endl; } A (inti) {a= B =i; cout<<"A constructor for a parameter"<<Endl; } A (intIintj) {a=i; b=J; cout<<"a two constructor for a parameter"<<Endl; }};classb{ Public:    intA, B;    A x; B () {a= B =2; cout<<"B Default constructor"<<Endl; } B (inti) {a= B =i; cout<<"B constructor for one parameter"<<Endl; } B (intIintj);}; B::b (intIintJ): A (i), B (j), X (A (3,4)){}//Initializes a member with a constructor with parameters, with an initialization listintMain () {A m; cout<<"---------------"<<Endl;    B N; cout<<"---------------"<<Endl; B N1 (4,5); cout<<"---------------"<<Endl; N.x= A (6,7); cout<<"---------------"<<Endl; cout<< n.x.a << n.x.b <<Endl; return 0;}

If you do not have to initialize the list, in the constructor with two variables of the constructor to assign x value, the result is

#include <iostream>using namespacestd;classa{ Public:    intA, B; A () {a= B =0; cout<<"A Default constructor"<<Endl; } A (intIintj) {a=i; b=J; cout<<"a two constructor for a parameter"<<Endl; }};classb{ Public:    intA, B;    A x; B () {a= B =2; X= A (1,2);//This is no longer initialized.                     Instead, the value is re-assigned. //The x is generated with the default constructor of a, and a temporary variable is constructed with a, which assigns the temporary variable to x through the assignment function.cout <<"B Default constructor"<<Endl; }};intMain () {B n; return 0;}

Class member pointers

1. Declare the class member pointer in the following way: int hyong::* P1 declares a pointer to an integer member in the class P1. Int (hyong::* p2) () Note the parentheses, declaring a pointer to a parameterless function that has an inverse type of int P2

2. A pointer to a member of a class refers to pointers to members in the classes, rather than pointers to a member of the object, which is not the same as pointer p=&m.a.

　　 The class member pointer provides the offset of the member's object in the class, not a true pointer.

Because it is not a real pointer, you cannot access the members of the class through pointers , but only through special operators. * or->* to access the members pointed to by the pointer.

For example, *p1=2, Hyong::* p1=2 is wrong and cannot be assigned directly to a class member that the class member pointer points to. Cout<<*p1<

"C + +" various member variables