The constructor of the "C + + Learning path" derived class (i)

The constructor of a simple derived class:

1. The so-called simple derived class refers to derived classes that do not contain inline objects of the base class.

2. In general, the constructor of such a derived class is in the form of:

int string int sid): Person (i, nam) {stuid = SID;}

Person (is the base class's initialization list )

3. Use of initialization lists for constructors

3.1 All constructors can take an initialization table of parameters to construct data members that belong to them entirely , such as:

1#include <iostream>2 using namespacestd;3 classA4 {5  Public:6AintA):d Ataa (a) {cout <<"call A's constructor"<<Endl;}7 Private:8     intDataa;9 };Ten voidMain () One { AA A (2); -}

　　

3.2 However, it is important to note that derived classes cannot directly use the initialization table of a parameter when constructing a base class component

    B (intint" call B's constructor " << Endl;} Error!!

3.3 It is not possible to write other statements such as output statements:

B (intint" call B's constructor " << endl{}//Error!!!!)

　　

3.4 It is possible to call the constructor of the base class and the initialization table of the data member at the same time

1#include <iostream>2 using namespacestd;3 classA4 {5  Public:6AintA):d Ataa (a) {cout <<"call A's constructor"<<Endl;}7 Private:8     intDataa;9 };Ten classB: PublicA One { A     intDatab; -  Public: -BintBintA): A (a), Datab (b) {cout <<"Call B's constructor"<<Endl;} the }; - voidMain () - { -b b (2,5); +}

 -     B (intint" call B's constructor " << Endl;}

This is the line of code, Datab (b) refers to the initialization list to write, a (a) is the base class constructor, which is very concise.

and the order of the code is independent of the position of Datab (b), which is to initialize a (a) first, then initialize the Datab, and finally execute the function body.

　　

3.5 Such writing is however not possible:

14 B ( int b, int a): A (a) { datab (b); cout << call B's constructor "

B (intint" call B's constructor " << Endl;} Error!!

This is the correct wording:

B (intint" call B's constructor " << Endl;}

　　

The constructor of the "C + + Learning path" derived class (i)