Introduction to Classes

Question 1

What is the focus in procedural programming?

Answer 1

To create functions that implement our program logic. We pass data objects to these functions, those functions perform operations on the data and potentially return a result

Question 2

What is the focus in object-oriented programming?

Answer 2

To create program defined data types that contain properties and well defined behaviours

Question 3

class invariant

Answer 3

a condition that must be true for the lifetime of an object for the object to remain in a valid state

Question 4

invalid state

Answer 4

an object that has a violated class invariant. Unexpected or undefined behaviour may result from further use of that object

Question 5

class

Answer 5

program defined compound type with data, and functions which work on that data

Question 6

member functions

Answer 6

functions that belong to a class type

Question 7

implicit object

Answer 7

the object that a member function is called on

Question 8

non member functions

Answer 8

name for functions that are not member functions

Question 9

what should you do if your class has no data members

Answer 9

use a namespace instead

Question 10

const member functions

Answer 10

member function that guarantees it will not modify the object or call any non-const member functions (as they may modify the object)

a member function that does not (and will not ever) modify the state of the object should be made const, so that it can be called on both non-const and const objects

Question 11

access level

Answer 11

each member of a class has an access level that determines who can access that member.

access levels are defined on a per class basis not a per object basis

Question 12

access controls

Answer 12

access level system informally called this

Question 13

public members

Answer 13

members of a class type that do not have any restrictions on how they can be accessed. Public members can be accessed by anyone (as long as they are in scope). This includes other members of the same class or code outside of the class

Question 14

the public

Answer 14

code that exists outside the members of a given class type

includes:
non-member functions
members of other class types

Question 15

What is the default access level for all members of a struct?

Answer 15

public

Question 16

private members

Answer 16

members of a class type that can only be accessed by other members of the same class

Question 17

What is the default access level for all members of a class?

Answer 17

private

Question 18

is a class with private members an aggregate?

Answer 18

no and therefore it cannot use aggregate initialisation

Question 19

how should you name private members?

Answer 19

starting with a m_ prefix. his helps distinguih them from the names of local variables, function parameters and member functions

Question 20

access specifier

Answer 20

allows you to explicitly set the access level of our members

Question 21

should structs use access specifiers?

Answer 21

they should avoid them, therefore all their members default to public

Question 22

access function

Answer 22

a trivial public member function whose job is to retrieve or change the value of a private member variable. Access function come in two flavours: getters and setters

Question 23

Getters

Answer 23

sometimes called accessors, are public member functions that return the value of a private member variable

Question 24

setters

Answer 24

sometimes called mutators, are public member fucntions that set the value of a private member variable.

Question 25

interface

Answer 25

this determines how a user of the class type will interact with objects of the class type. Because only public members can be accessed from outside of the class type, the public members of a class type form its interface.

Question 26

public interface

Answer 26

an interface composed of only public members

Question 27

implementation of a class type

Answer 27

the code that actually makes the class behave as intended. This includes both the member variables that store data, and the bodies of the member functions that contain the program logic and manipulate the member variables

Question 28

data hiding / information hiding / data abstraction

Answer 28

technique used to enforcethe separation of the interface and implementation by hiding the implementation of a program defined data type from users

Question 29

encapsulation

Answer 29

sometimes used to refer to data hiding or to refer to the bundling of data and functions together (without regard for access controls) so its use can be ambiguous

Question 30

What order should you define the members in your class and why?

Answer 30

Prefer to declare your public members first and your private members last. This spotlights the public interface and de-emphasises implementation details

Question 31

constructor

Answer 31

a special member function that is used to initialise class type objects. A matching constructor must be found in order to create a non-aggregate class type object

Question 32

member initialiser list

Answer 32

allows you to initialise your member variables from within a constructor. Member variables in a member initialiser should be listed in the order that they are defined in the class. Prefer using the member initialiser list to initialise your members over assigning values in the body of the constructor

Question 33

default constructor

Answer 33

a constructor that takes no parameters (or has all default parameters). The default constructor is used if no initialisation values are provided.

Question 34

implicit default constructor

Answer 34

If a non-aggregate class type object has no user-declared constructors, the compiler will generate a default constructor (so that the class can be value or default initialised)

Question 35

constructor chaining

Answer 35

when a constructor delegates construction to another constructor

Question 36

delegating constructors

Answer 36

a constructor that delegates using constructor chaining

Question 37

can constructors delegate and initialise

Answer 37

no only one or the other

Question 38

temporary / unamed / anonymous object

Answer 38

an object that has no name and exists only for the duration of a single expression

Question 39

copy constructor

Answer 39

a constructor you use to initialise an object with an existing object of the same type

Question 40

implicit copy constructor

Answer 40

if you do not provide a copy constructor for your class c++ will create a public one for you that does memberwise initialisation

Question 41

as-if rule

Answer 41

the compiler can modify a program however it likes in order to produce more optimised code, so long as those modifications do not affect a program’s observable behaviour

One exception to the rule is copy elision

Question 42

copy elision

Answer 42

a compiler optimization technique that allows the compiler to remove unnecessary copying of objects

Question 43

elided

Answer 43

we say the constructor has been elided when the compiler optimised away a call to the copy constructor

Question 44

user defined conversion

Answer 44

a function written to convert a value to or from a program defined type

Question 45

converting constructor

Answer 45

constructor that can be used to perform an implicit conversion

Question 46

are all constructors converting constructors?

Answer 46

they are in their default state

Question 47

explicit

Answer 47

we use this keyword to tell the compiler a constructor should not be used as a converting constructor

Question 48

what can explicit constructors not be used for?

Answer 48

copy initialisation
copy list initialisation
implcit conversions

Question 49

what constructors should you mark as explicit

Answer 49

any constructor that takes a single argument

Question 50

what constructors should you leave as implicit?

Answer 50

copy or move constructors (as these do not perform conversions)

cases where the conversion between types is both semantically equivalent and performant

Question 51

are constexpr member functions const?

Answer 51

not implicitly