{"id":934,"date":"2024-08-09T20:27:30","date_gmt":"2024-08-09T20:27:30","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=934"},"modified":"2025-01-24T20:33:51","modified_gmt":"2025-01-24T20:33:51","slug":"multiple-inheritance","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/multiple-inheritance\/","title":{"rendered":"Multiple Inheritance"},"content":{"rendered":"\n

<\/span>Multiple Inheritance<\/span><\/h2>\n\n\n\n

<\/span>What is Multiple Inheritance?<\/span><\/h3>\n\n\n\n

So far, we have seen only single inheritance<\/em>:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n
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A reminder: the arrows in an inheritance diagram point from a derived class<\/em> to its base class<\/em>.<\/p>\n<\/blockquote>\n\n\n\n

But a class may be derived from more than one base class:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Other examples might be:<\/p>\n\n\n\n

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\"\"<\/figure>\n<\/div>\n\n\n\n
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\"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n

<\/span>From Tree to DAG<\/span><\/h3>\n\n\n\n
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Note that multiple inheritance moves us away from a simple tree structure:<\/p>\n\n\n\n

\"\"<\/figure>\n<\/div>\n\n\n\n
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towards a Directed Acyclic Graph<\/em> — the dreaded DAG, or diamond shape:<\/p>\n\n\n\n

\"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n

<\/span>Example of Multiple Inheritance<\/span><\/h3>\n\n\n\n

A class indicates that it derives from more than one class by listing multiple classes in its inheritance list:<\/p>\n\n\n\n

class ToyTruck : public Toy, public Truck<\/strong>\n{\n   \/\/ ...\n}<\/code><\/pre>\n\n\n\n
Here’s an example of an implementation of a ‘toy’ multiple inheritance hierarchy, consisting of classes Toy, Barbie, Truck,<\/strong> and ToyTruck<\/strong>:<\/p>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Toy.h<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Toy_h<\/span><\/span>\n#define<\/span> Toy_h<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Toy<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>enum<\/span> <\/span>ToyType<\/span> { <\/span>Doll<\/span>, <\/span>ActionFigure<\/span>, <\/span>Vehicle<\/span> };<\/span><\/span>\n  <\/span><\/span>\n  <\/span>Toy<\/span>(<\/span>ToyType<\/span> <\/span>type<\/span>) : <\/span>m_type<\/span>(type) {}<\/span><\/span>\n  <\/span><\/span>\n  <\/span>ToyType<\/span> <\/span>GetType<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_type; }<\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\nprivate:<\/span><\/span>\n  ToyType m_type;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Toy_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Toy.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Toy.h"<\/span><\/span>\n<\/span>\nstatic<\/span> <\/span>std<\/span>::string toyType[] =<\/span><\/span>\n  { <\/span>"Doll"<\/span>, <\/span>"Action figure"<\/span>, <\/span>"Vehicle"<\/span> };<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Toy<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"Toy "<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>" Toy type: "<\/span> << <\/span>toyType<\/span>[m_type]<\/span><\/span>\n            << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Barbie.h<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Barbie_h<\/span><\/span>\n#define<\/span> Barbie_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"Toy.h"<\/span><\/span>\n<\/span>\n\/\/ Barbie.h<\/span><\/span>\nclass<\/span> <\/span>Barbie<\/span> : <\/span>public<\/span> <\/span>Toy<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>enum<\/span> <\/span>HairColor<\/span> { <\/span>Blond<\/span>, <\/span>Brunette<\/span>, <\/span>Redhead<\/span> };<\/span><\/span>\n  <\/span><\/span>\n  <\/span>Barbie<\/span>(<\/span>HairColor<\/span> <\/span>color<\/span>)<\/span><\/span>\n    : <\/span>Toy<\/span>(Doll), <\/span>m_hairColor<\/span>(color) {}<\/span><\/span>\n  <\/span>HairColor<\/span> <\/span>GetHairColor<\/span>() { <\/span>return<\/span> m_hairColor; }<\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\nprivate:<\/span><\/span>\n  HairColor m_hairColor;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Barbie_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Barbie.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Barbie.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Barbie<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n  <\/span>static<\/span> <\/span>std<\/span>::string hairType[] =<\/span><\/span>\n    { <\/span>"Blond"<\/span>, <\/span>"Brunette"<\/span>, <\/span>"Redhead"<\/span> };<\/span><\/span>\n  <\/span>Toy<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>" Hair color: "<\/span><\/span>\n            << <\/span>hairType<\/span>[m_hairColor]<\/span><\/span>\n            << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Truck.h<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Truck_h<\/span><\/span>\n#define<\/span> Truck_h<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Truck<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Truck<\/span>(<\/span>double<\/span> <\/span>hp<\/span>, <\/span>bool<\/span> <\/span>isFwd<\/span>)<\/span><\/span>\n    : <\/span>m_hp<\/span>(hp), <\/span>m_is_fwd<\/span>(isFwd) {}<\/span><\/span>\n  <\/span><\/span>\n  <\/span>double<\/span> <\/span>GetHorsePower<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_hp; }<\/span><\/span>\n  <\/span>bool<\/span> <\/span>IsFourWheelDrive<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_is_fwd; }<\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\nprivate:<\/span><\/span>\n  <\/span>double<\/span> m_hp;<\/span>  \/\/ Horsepower<\/span><\/span>\n  <\/span>bool<\/span>   m_is_fwd;<\/span>  \/\/ Is 4-wheel drive<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Truck_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  Truck.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Truck.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Truck<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"Truck:"<\/span> << <\/span>std<\/span>::endl<\/span><\/span>\n            << <\/span>" Horsepower: "<\/span> << m_hp << <\/span>std<\/span>::endl<\/span><\/span>\n            << <\/span>" Four wheel drive: "<\/span><\/span>\n            << ((m_is_fwd)? <\/span>"Yes"<\/span> : <\/span>"No"<\/span>)<\/span><\/span>\n            << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  ToyTruck.h<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> ToyTruck_h<\/span><\/span>\n#define<\/span> ToyTruck_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"Toy.h"<\/span><\/span>\n#include<\/span> <\/span>"Truck.h"<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>ToyTruck<\/span> : <\/span>public<\/span> <\/span>Toy<\/span>, <\/span>public<\/span> <\/span>Truck<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>ToyTruck<\/span>() : <\/span>Toy<\/span>(Vehicle), <\/span>Truck<\/span>(<\/span>0<\/span>, <\/span>false<\/span>) {}<\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* ToyTruck_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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\/\/<\/span><\/span>\n\/\/  ToyTruck.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"ToyTruck.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>ToyTruck<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"ToyTruck: "<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>Toy<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>Truck<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
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Here’s the main program:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Toy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Barbie.h"<\/span><\/span>\n#include<\/span> <\/span>"Truck.h"<\/span><\/span>\n#include<\/span> <\/span>"ToyTruck.h"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  Barbie <\/span>barbie<\/span>(<\/span>Barbie<\/span>::Blond);<\/span><\/span>\n  Truck  <\/span>truck<\/span>(<\/span>450<\/span>, <\/span>true<\/span>);<\/span><\/span>\n  ToyTruck toyTruck;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"barbie is "<\/span>;<\/span><\/span>\n  <\/span>barbie<\/span>.<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"truck is "<\/span>;<\/span><\/span>\n  <\/span>truck<\/span>.<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"toyTruck is "<\/span>;<\/span><\/span>\n  <\/span>toyTruck<\/span>.<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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Which outputs:<\/p>\n\n\n\n
barbie is Toy \n Toy type: Doll\n Hair color: Blond\ntruck is Truck:\n Horsepower: 450\n Four wheel drive: Yes\ntoyTruck is ToyTruck: \nToy \n Toy type: Vehicle\nTruck:\n Horsepower: 0\n Four wheel drive: No\nProgram ended with exit code: 0<\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Multiple Inheritance Concepts<\/span><\/h3>\n\n\n\n
The order of derivation is not important, except for constructor initialization, destructor cleanup, and possibly storage layout.<\/p>\n\n\n\n
A class listed in the base class list is a direct base class<\/em> of the derived class.<\/p>\n\n\n\n
An indirect base class <\/em>is one which is not a direct base class, but is a base class of one of the direct base classes. <\/p>\n\n\n\n
Got that?<\/strong><\/p>\n\n\n\n
A direct base class may not be specified in the base class list more than once:<\/p>\n\n\n\n
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class<\/span> <\/span>X<\/span> : <\/span>public<\/span> <\/span>A<\/span>, <\/span>public<\/span> <\/span>B<\/span>, <\/span>public<\/span> <\/span>A<\/span> \/\/ compile-time error\u00a0<\/span><\/span>\n{<\/span><\/span>\n\u00a0\u00a0\u00a0\/\/ ...<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
<\/div>\n<\/div>\n\n\n\n
However, a class may be an indirect base class more than once<\/em>:<\/p>\n\n\n\n
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class<\/span> <\/span>A<\/span> : { ... };<\/span><\/span>\nclass<\/span> <\/span>B<\/span> : <\/span>public<\/span> <\/span>A<\/span> { ... };<\/span><\/span>\nclass<\/span> <\/span>C<\/span> : <\/span>public<\/span> <\/span>A<\/span> { ... };<\/span><\/span>\nclass<\/span> <\/span>X<\/span> : <\/span>public<\/span> <\/span>A<\/span>, <\/span>public<\/span> <\/span>B<\/span><\/span>\n{<\/span><\/span>\n\t\/\/ ...<\/span><\/span>\n};<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
<\/div>\n<\/div>\n\n\n\n
<\/span>Multiple Inheritance and Constructors<\/span><\/h3>\n\n\n\n
The order of constructor execution is:<\/p>\n\n\n\n
    \n
  1. Base class constructor(s)<\/em>, in declaration order (independent of initializer list order)<\/li>\n\n\n\n
  2. Derived class member constructor(s)<\/em>, in declaration order (independent of initializer list order) <\/li>\n\n\n\n
  3. The body of the derived class constructor<\/em>.<\/li>\n<\/ol>\n\n\n\n
    Virtual base classes<\/em> are a special case (see later).<\/p>\n\n\n\n
    <\/span>Multiple Inheritance and Destructors<\/span><\/h3>\n\n\n\n
    The order of destructor execution is:<\/p>\n\n\n\n
      \n
    1. The body of the derived class destructor<\/em>.<\/li>\n\n\n\n
    2. Derived class member destructor(s)<\/em>, in reverse declaration order<\/li>\n\n\n\n
    3. Base class destructor(s)<\/em>, in reverse declaration order<\/li>\n<\/ol>\n\n\n\n
      In other words, the exact opposite of constructor execution order<\/em>.<\/p>\n\n\n\n
      Again, virtual base classes<\/em> are a special case (see later).<\/p>\n\n\n\n
      <\/span>Mixins<\/span><\/h3>\n\n\n\n
      A common use of multiple inheritance is the addition of service protocols to class hierarchies:<\/p>\n\n\n\n
      class Person : public Persistant, public Sortable\n{ ... };\n\nclass Shape : public Persistant, public Listable\n{ ... };<\/strong>\n<\/code><\/pre>\n\n\n\n
      This is called mixin<\/em> inheritance — apparently from a common practice among ice cream stores of mixing candies, etc., into ice cream:<\/p>\n\n\n\n
      class Scoop : public Jimmies, public M_and_Ms\n{ ... };<\/strong><\/code><\/pre>\n\n\n\n
      <\/span>Member Access under Multiple Inheritance<\/span><\/h3>\n\n\n\n
      Access to base class members must be unambiguous<\/em>.<\/p>\n\n\n\n
      The check for ambiguity takes place before access control<\/em>:<\/p>\n\n\n\n
      \n
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      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Ambiguous Member Access<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>One<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>int<\/span> i;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Two<\/span><\/span>\n{<\/span><\/span>\nprivate:<\/span><\/span>\n  <\/span>int<\/span> i;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>OneTwo<\/span> : <\/span>public<\/span> <\/span>One<\/span>, <\/span>public<\/span> <\/span>Two<\/span><\/span>\n{<\/span><\/span>\n  \/\/ no additional members<\/span><\/span>\n};<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  OneTwo ot;<\/span><\/span>\n  <\/span>ot<\/span>.<\/span>i<\/span> = <\/span>10<\/span>;<\/span>       \/\/ ERROR: ambiguous<\/span><\/span>\n  <\/span>ot<\/span>.<\/span>One<\/span>::i = <\/span>11<\/span>;<\/span>  \/\/ OK<\/span><\/span>\n  <\/span>ot<\/span>.<\/span>Two<\/span>::i = <\/span>12<\/span>;<\/span>  \/\/ ERROR: no access<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
      \n
      main.cpp:28:6 Member 'i' found in multiple base classes of different types\n\nmain.cpp:30:11 'i' is a private member of 'Two'\n<\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
      <\/span>Further Exploration<\/span><\/h3>\n\n\n\n
      Let’s implement our Person \/ Student \/ Employee \/ TeachingAssistant<\/strong> example:<\/p>\n\n\n\n
      \n
      \n
      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  Taxonomy.h<\/span><\/span>\n\/\/  Multiple Inheritance - Taxonomy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Taxonomy_h<\/span><\/span>\n#define<\/span> Taxonomy_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><string><\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Person<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getName<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_name; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span> = <\/span>0<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n  <\/span>std<\/span>::string m_name;<\/span>  \/\/ Person name<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class Student<\/span><\/span>\nclass<\/span> <\/span>Student<\/span> : <\/span>public<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Student<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>, <\/span>int<\/span> <\/span>id<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Student<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>int<\/span> <\/span>GetId<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_sid; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>double<\/span> <\/span>GetGpa<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_sgpa; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>SetGpa<\/span>(<\/span>double<\/span> <\/span>gpa<\/span>)<\/span><\/span>\n  { m_sgpa = gpa; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n    <\/span>int<\/span>    m_sid;<\/span>  \/\/ Student ID<\/span><\/span>\n    <\/span>double<\/span> m_sgpa;<\/span>  \/\/ Grade Point Average<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class Employee<\/span><\/span>\nclass<\/span> <\/span>Employee<\/span> : <\/span>public<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Employee<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>, <\/span>double<\/span> <\/span>salary<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Employee<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>double<\/span> <\/span>GetSalary<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_salary; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n    <\/span>double<\/span>  m_salary;<\/span>  \/\/ Employee salary<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class TeachingAssistant<\/span><\/span>\nclass<\/span> <\/span>TeachingAssistant<\/span> : <\/span>public<\/span> <\/span>Student<\/span>,<\/span><\/span>\n                          <\/span>public<\/span> <\/span>Employee<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>TeachingAssistant<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>,<\/span><\/span>\n                    <\/span>int<\/span> <\/span>id<\/span>, <\/span>double<\/span> <\/span>salary<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~TeachingAssistant<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n<\/span>\n#endif<\/span> \/* Taxonomy_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
      \n
      … and we instrument the constructors and destructors, in order to see what’s happening:<\/p>\n\n\n\n
      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  Taxonomy.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Taxonomy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"Taxonomy.h"<\/span><\/span>\n<\/span>\n\/\/ class Person<\/span><\/span>\nPerson<\/span>::<\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name)<\/span><\/span>\n  : <\/span>m_name<\/span>(name)<\/span><\/span>\n{ <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Person()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nPerson<\/span>::~<\/span>Person<\/span>()<\/span><\/span>\n{ <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Person()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Person<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Name: "<\/span> << m_name << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class Student<\/span><\/span>\nStudent<\/span>::<\/span>Student<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name, <\/span>int<\/span> id)<\/span><\/span>\n  : <\/span>Person<\/span>(name), <\/span>m_sid<\/span>(id), <\/span>m_sgpa<\/span>(<\/span>0.0<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Student()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nStudent<\/span>::~<\/span>Student<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Student()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Student<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    <\/span>Person<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Id:  "<\/span> << m_sid << <\/span>std<\/span>::endl<\/span><\/span>\n              << <\/span>"GPA: "<\/span> << m_sgpa << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class Employee<\/span><\/span>\nEmployee<\/span>::<\/span>Employee<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name, <\/span>double<\/span> salary)<\/span><\/span>\n  : <\/span>Person<\/span>(name), <\/span>m_salary<\/span>(salary)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Employee()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nEmployee<\/span>::~<\/span>Employee<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Employee()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Employee<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    <\/span>Person<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Salary: "<\/span> << m_salary << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class TeachingAssistant<\/span><\/span>\nTeachingAssistant<\/span>::<\/span>TeachingAssistant<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name,<\/span><\/span>\n                  <\/span>int<\/span> id, <\/span>double<\/span> salary)<\/span><\/span>\n  : <\/span>Student<\/span>(name, id), <\/span>Employee<\/span>(name, salary)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In TeachingAssistant()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nTeachingAssistant<\/span>::~<\/span>TeachingAssistant<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~TeachingAssistant()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>TeachingAssistant<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    <\/span>Student<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n    <\/span>Employee<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
      \n
      \n
      Here’s a simple main program:<\/p>\n\n\n\n
      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Taxonomy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Taxonomy.h"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  TeachingAssistant <\/span>ta<\/span>(<\/span>"Fred Bloggs"<\/span>,<\/span><\/span>\n                       <\/span>57<\/span>, <\/span>3000.00<\/span>);<\/span><\/span>\n  <\/span>ta<\/span>.<\/span>Print<\/span>();<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
      \n
      … which produces the following output:<\/p>\n\n\n\n
      In Person()<\/strong>\nIn Student()\nIn Person()<\/strong>\nIn Employee()\nIn TeachingAssistant()\nName: Fred Bloggs<\/strong>\nId:  57\nGPA: 0\nName: Fred Bloggs<\/strong>\nSalary: 3000\nIn ~TeachingAssistant()\nIn ~Employee()\nIn ~Person()<\/strong>\nIn ~Student()\nIn ~Person()<\/strong>\nProgram ended with exit code: 0<\/code><\/pre>\n\n\n\n
      Can you explain this?<\/p>\n<\/div>\n<\/div>\n\n\n\n
      \n
      \n
      What we wanted was a hierarchy like:<\/p>\n\n\n\n
      \"\"<\/figure>\n<\/div>\n\n\n\n
      \n
      But what we actually have is a hierarchy like:<\/p>\n\n\n\n
      \"\"<\/figure>\n<\/div>\n<\/div>\n\n\n\n
      How do we fix this?<\/p>\n\n\n\n
      <\/span>Virtual Base Classes<\/span><\/h3>\n\n\n\n
      Because a class can be an indirect base class to a derived class more than once, C++ provides a way to optimize the way such base classes work. Virtual base classes offer a way to save space and avoid ambiguities in class hierarchies that use multiple inheritance.<\/p>\n\n\n\n
      Each nonvirtual object contains a copy of the data members defined in the base class. This duplication wastes space and requires you to specify which copy of the base class members you want whenever you access them.<\/p>\n\n\n\n
      When a base class is specified as a virtual base, it can act as an indirect base more than once without duplication of its data members. A single copy of its data members is shared by all the base classes that use it as a virtual base.<\/p>\n\n\n\n
      When declaring a virtual base class, the virtual<\/code><\/strong> keyword appears in the base lists of the derived classes.<\/p>\n\n\n\n
      \n
      \n
      To user virtual base classes<\/em> in our example, we make the following changes:<\/p>\n\n\n\n
      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  Taxonomy.h<\/span><\/span>\n\/\/  Multiple Inheritance - Taxonomy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Taxonomy_h<\/span><\/span>\n#define<\/span> Taxonomy_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><string><\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Person<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getName<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_name; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span> = <\/span>0<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n  <\/span>std<\/span>::string m_name;<\/span>  \/\/ Person name<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class Student<\/span><\/span>\nclass<\/span> <\/span>Student<\/span> : <\/span>public<\/span> <\/span>virtual<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Student<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>, <\/span>int<\/span> <\/span>id<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Student<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>int<\/span> <\/span>GetId<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_sid; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>const<\/span> <\/span>double<\/span> <\/span>GetGpa<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_sgpa; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>SetGpa<\/span>(<\/span>double<\/span> <\/span>gpa<\/span>)<\/span><\/span>\n  { m_sgpa = gpa; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n    <\/span>int<\/span>    m_sid;<\/span>  \/\/ Student ID<\/span><\/span>\n    <\/span>double<\/span> m_sgpa;<\/span>  \/\/ Grade Point Average<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class Employee<\/span><\/span>\nclass<\/span> <\/span>Employee<\/span> : <\/span>public<\/span> <\/span>virtual<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>Employee<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>, <\/span>double<\/span> <\/span>salary<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~Employee<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>double<\/span> <\/span>GetSalary<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_salary; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n  <\/span><\/span>\nprivate:<\/span><\/span>\n    <\/span>double<\/span>  m_salary;<\/span>  \/\/ Employee salary<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ class TeachingAssistant<\/span><\/span>\nclass<\/span> <\/span>TeachingAssistant<\/span> : <\/span>public<\/span> <\/span>Student<\/span>,<\/span><\/span>\n                          <\/span>public<\/span> <\/span>Employee<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>TeachingAssistant<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>name<\/span>,<\/span><\/span>\n                    <\/span>int<\/span> <\/span>id<\/span>, <\/span>double<\/span> <\/span>salary<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>~TeachingAssistant<\/span>();<\/span><\/span>\n  <\/span><\/span>\n  <\/span>virtual<\/span> <\/span>void<\/span> <\/span>Print<\/span>() <\/span>const<\/span>;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n<\/span>\n#endif<\/span> \/* Taxonomy_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
      \n
      … and also make changes here:<\/p>\n\n\n\n
      <\/path><\/path><\/svg><\/span>
      \/\/<\/span><\/span>\n\/\/  Taxonomy.cpp<\/span><\/span>\n\/\/  Multiple Inheritance - Taxonomy<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 8\/30\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"Taxonomy.h"<\/span><\/span>\n<\/span>\n\/\/ class Person<\/span><\/span>\nPerson<\/span>::<\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name)<\/span><\/span>\n  : <\/span>m_name<\/span>(name)<\/span><\/span>\n{ <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Person()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nPerson<\/span>::~<\/span>Person<\/span>()<\/span><\/span>\n{ <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Person()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Person<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Name: "<\/span> << m_name << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class Student<\/span><\/span>\nStudent<\/span>::<\/span>Student<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name, <\/span>int<\/span> id)<\/span><\/span>\n  : <\/span>Person<\/span>(name), <\/span>m_sid<\/span>(id), <\/span>m_sgpa<\/span>(<\/span>0.0<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Student()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nStudent<\/span>::~<\/span>Student<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Student()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Student<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    \/\/ Person::Print(); - Removed<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Id:  "<\/span> << m_sid << <\/span>std<\/span>::endl<\/span><\/span>\n              << <\/span>"GPA: "<\/span> << m_sgpa << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class Employee<\/span><\/span>\nEmployee<\/span>::<\/span>Employee<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name, <\/span>double<\/span> salary)<\/span><\/span>\n  : <\/span>Person<\/span>(name), <\/span>m_salary<\/span>(salary)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In Employee()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nEmployee<\/span>::~<\/span>Employee<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~Employee()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>Employee<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n    \/\/ Person::Print(); - Removed<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"Salary: "<\/span> << m_salary << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ class TeachingAssistant<\/span><\/span>\nTeachingAssistant<\/span>::<\/span>TeachingAssistant<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name,<\/span><\/span>\n                  <\/span>int<\/span> id, <\/span>double<\/span> salary)<\/span><\/span>\n  : <\/span>Person<\/span>(name),<\/span> \/\/ Added<\/span><\/span>\n    <\/span>Student<\/span>(name, id), <\/span>Employee<\/span>(name, salary)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In TeachingAssistant()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nTeachingAssistant<\/span>::~<\/span>TeachingAssistant<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"In ~TeachingAssistant()"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>TeachingAssistant<\/span>::<\/span>Print<\/span>() <\/span>const<\/span><\/span>\n{<\/span><\/span>\n  <\/span>Person<\/span>::<\/span>Print<\/span>();<\/span> \/\/ Added<\/span><\/span>\n  <\/span>Student<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n  <\/span>Employee<\/span>::<\/span>Print<\/span>();<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
      With no further changes, the exact same main program produces:<\/p>\n\n\n\n
      In Person()\nIn Student()\nIn Employee()\nIn TeachingAssistant()\nName: Fred Bloggs\nId:  57\nGPA: 0\nSalary: 3000\nIn ~TeachingAssistant()\nIn ~Employee()\nIn ~Student()\nIn ~Person()\nProgram ended with exit code: 0<\/code><\/pre>\n\n\n\n
      <\/span>Points to note:<\/span><\/h4>\n\n\n\n
      The virtualness of Person<\/strong> is a property of the derivation<\/em>, not a property of Person<\/strong> itself.<\/p>\n\n\n\n
      A class may be both an ordinary class and a virtual base in the same inheritance hierarchy.<\/p>\n\n\n\n
      One may cast from a derived class to a virtual base class, but not from a virtual base class to a derived class<\/em>.<\/p>\n\n\n\n
      <\/span>Constructors and Virtual Base Classes<\/span><\/h3>\n\n\n\n
      Constructors for virtual base classes<\/em> are a special case:<\/p>\n\n\n\n
        \n
      • Virtual bases are constructed before any non-virtual classes<\/em>.<\/li>\n\n\n\n
      • Virtual bases are constructed in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes<\/em>.<\/li>\n\n\n\n
      • ‘Left-to-right’ is the order of appearance of the base class names in the declaration of the derived class.<\/li>\n\n\n\n
      • If a virtual base class does not have a default constructor, it must be explicitly initialized by every derived class<\/em>.<\/li>\n<\/ul>\n\n\n\n
        <\/span>Destructors and Virtual Base Classes<\/span><\/h3>\n\n\n\n
        Destructors for virtual base classes are called in the reverse order of their appearance in a directed acyclic graph (depth-first, left-to-right, postorder traversal). <\/p>\n\n\n\n
        \n
        This area of C++ is definitely arcane! <\/p>\n<\/blockquote>\n\n\n\n
        <\/span>The Complexities of Multiple Inheritance<\/span><\/h2>\n\n\n\n
        Multiple inheritance is much more complex<\/em> than single inheritance.<\/p>\n\n\n\n
          \n
        • There is one case where multiple inheritance is simple: when inheriting from disjoint base classes <\/em>— for example, adding mixins.<\/li>\n\n\n\n
        • Even in the simple case, there is the possibility of name conflicts among the base class members.<\/li>\n\n\n\n
        • When a common single instance of a base class is desired, it is necessary to use virtual base classes<\/em> — which introduces more complexity.<\/li>\n<\/ul>\n\n\n\n
          \n
          Bottom Line: Avoid Multiple Inheritance as far as possible. It’s a quagmire!<\/strong><\/p>\n<\/blockquote>\n\n\n\n
          <\/p>\n","protected":false},"excerpt":{"rendered":"
          Multiple Inheritance What is Multiple Inheritance? So far, we have seen only single inheritance: A reminder: the arrows in an inheritance diagram point from a derived class to its base class. But a class may be derived from more than one base class: Other examples might be: From Tree to DAG Note that multiple inheritance […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":910,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-934","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/934","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/comments?post=934"}],"version-history":[{"count":13,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/934\/revisions"}],"predecessor-version":[{"id":1787,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/934\/revisions\/1787"}],"up":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/910"}],"wp:attachment":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/media?parent=934"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}