Intermediate C++ Game Programming Tutorial 17

This two-part lesson teaches the basics of inheritance, how it works and what motivates its use, with ample concrete coding examples. Also taught here is the keyword mutable, for some reason.

Topics Covered

Part 1

• How to inherit from a class
• Referencing a child type with a parent reference/ptr
• Inheritance and constructors
• Overriding parent functions
• Invoking overridden versions of functions
• Access specifier protected

Part 2

• Hierarchical inheritance
• Abstract vs. concrete classes
• mutable data members

Video Timestamp Index

Tutorial 17.1

• What is inheritance? Introducing a simple example class B : public A {...};0:15
• Different language used for the same concept 1:45:
  • to "inherit" a class, from "parent" to "child",
  • to "extend" a class, from "base" to "extended",
  • to "derive" a class, from "base" to "derived",
  • to "sub-class" a class, from "superclass" to "subclass" (used in Java)
• Why is inheritance important? no clutter, no repetition of code, no tampering inside deployed classes 2:44
• Fictitious but instructive Smasher and EliteSmasher class example 5:08
• Inheritance creates an "Is-a relationship" 8:15
  • A child class "is-a [kind of]" parent class, so you can pass a child object to functions that expect a reference to a parent object
• WORK-IN-PROGRESS

Tutorial 17.2

• WORK-IN-PROGRESS

Part 2 Class Specification

All of the MemeFighter entities of the system will have the following shared functionality:

• Member data for name (string), hp, speed, and power (int)
• Getters for name, initiative (speed + 2d6), and alive state
• Punch function that takes a different entity and applies damage (str + 2d6) to it
• Tick function where the entity recovers 1d6 hp

Functions should narrate actions / effects when it makes sense. Tests should be made to check whether an entity is alive before an action is performed (dead characters can't punch, recover, etc.)

There are two concrete MemeFighter entites: MemeFrog and MemeStoner

MemeFrog:

• Has 69 hp, 7 speed, and 14 power
• Has a SpecialMove function that takes an entity and has a 1/3 chance of dealing 3d6 + 20 damage
• Takes 1d6 of damage every turn

MemeStoner:

• Has 80 hp, 4 speed, and 10 power
• Has a SpecialMove function that takes no parameters and has a 1/2 chance of adding 3 speed, increasing power by 69/42, adding 10 hp, and adding to the entity's name

Source Code

Inheritance Github Repository

Links

C++ FAQ on protected
Stack Overflow question about inheritance

See also

• Next in series (Tutorial 18)
• Intermediate C++ Game Programming Series