References and Pointers

Question 1

Compound / Composite Data Types

Answer 1

data types that can be constructed from fundamental data types or other compound data types

Question 2

Value category of an expression

Answer 2

this indicates whether the expression resolves to a value, a function, or an object of some kind

Question 3

lvalue

Answer 3

an expression that evaluates to a function or an object that has an identity (e.g. an identifier or an identifiable memory address)

Question 4

two subtypes of lvalues

Answer 4

modifiable and non-modifiable

Question 5

rvalue

Answer 5

an expression which is not an lvalue. Includes literals (except string literals) and return values of functions or operators when returned by value

Question 6

reference

Answer 6

an alias for an existing object

once the reference has been defined, any operation on the reference is applied to the object being referenced

Question 7

Two types of references in C++

Answer 7

lvalue references and rvalue references

Question 8

lvalue reference

Answer 8

commonly called a reference

acts as an alias for an existing lvalue (such as a variable)

Question 9

term for when a reference is initialized with an object or function

Answer 9

bound to it

Question 10

referent

Answer 10

object or function being referenced by a reference

Question 11

why are lvalue references occasionally called lvalue references to non-const

Answer 11

Lvalue references can’t be bound to non-modifiable lvalues or rvalues (otherwise you’d be able to change those values through the reference, which would be a violation of their const-ness)

Question 12

references: reseated

Answer 12

Once initialized, a reference in C++ cannot be reseated, meaning it can not be changed to reference another object.

Question 13

dangling reference

Answer 13

When an object being referenced is destroyed before a reference to it, the reference is left referencing an object that no longer exists.

Accessing a dangling reference leads to undefined behavior.

Question 14

lvalue reference to a const value aka reference to const aka const reference

Answer 14

By using the const keyword when declaring an lvalue reference, we tell an lvalue reference to treat the object it is referencing as const.

Const references can bind to modifiable lvalues, non-modifiable lvalues, and rvalues.

Question 15

temporary object / unnamed object / anonymous object

Answer 15

an object that is created for temporary use (and then destroyed) within a single expression.

Question 16

pass by reference

Answer 16

declare a function parameter as a reference (or const reference) rather than as a normal variable. When the function is called, each reference parameter is bound to the appropriate argument.

Because the reference acts as an alias for the argument, no copy of the argument is made.

Question 17

address-of operator

Answer 17

&

returns the memory address of its operand

Question 18

dereference operator

Answer 18

*

Dereferences a pointer by returning the value at a given memory address as an lvalue

int value {10};
int *ptr { &value }; // ptr hold address of value

int dereferencedValue { *ptr };

Question 19

pointer

Answer 19

is an object that holds a memory address (typically of another variable) as its value. This allows us to store the address of some other object to use later. Like normal variables, pointers are not initialized by default.

Question 20

wild pointer

Answer 20

A pointer that has not been initialized

Question 21

dangling pointer

Answer 21

is a pointer that is holding the address of an object that is no longer valid (e.g. because it has been destroyed).

Question 22

nullptr

Answer 22

Besides a memory address, there is one additional value that a pointer can hold: a null value. When a pointer is holding a null value, it means the pointer is not pointing at anything.

represents a null pointer literal

Question 23

Rules for working with pointers

Answer 23

A pointer should either hold the address of a valid object, or be set to nullptr. That way we only need to test pointers for null, and can assume any non-null pointer is valid.

Question 24

pointer to a const value

Answer 24

(sometimes called a pointer to const for short) is a (non-const) pointer that points to a constant value.

Question 25

const pointer

Answer 25

is a pointer whose address can not be changed after initialization.

Question 26

const pointer to a const value

Answer 26

can not have its address changed, nor can the value it is pointing to be changed through the pointer

Question 27

pass by address

Answer 27

instead of providing an object as an argument, the caller provides an object’s address (via a pointer). This pointer (holding the address of the object) is copied into a pointer parameter of the called function (which now also holds the address of the object). The function can then dereference that pointer to access the object whose address was passed.

Question 28

Return by reference

Answer 28

returns a reference that is bound to the object being returned, which avoids making a copy of the return value.

Using return by reference has one major caveat: the programmer must be sure that the object being referenced outlives the function returning the reference. Otherwise, the reference being returned will be left dangling (referencing an object that has been destroyed), and use of that reference will result in undefined behavior.

If a parameter is passed into a function by reference, it’s safe to return that parameter by reference.

Question 29

If a function returns a reference, and that reference is used to initialize or assign to a non-reference variable…

Answer 29

…the return value will be copied (as if it had been returned by value).

Question 30

auto keyword for variables

Answer 30

Type deduction for variables (via the auto keyword) will drop any reference or top-level const qualifiers from the deduced type. These can be reapplied as part of the variable declaration if desired.

Question 31

Return by address

Answer 31

works almost identically to return by reference, except a pointer to an object is returned instead of a reference to an object