C++ Primer, Fifth Edition: Pointers versus References: Understanding Aliases and Addresses

The Anatomy of Compound Types

C++ compound types are defined by combining a base type with a type modifier. While both references and pointers provide indirection, they are philosophically distinct. A Reference (&) is a permanent alias—a nickname for an existing object. Once bound, it cannot be reseated. Conversely, a Pointer (*) is an independent object in memory that stores a hexadecimal address. It can be redirected to different objects or set to nullptr.

Visualizing the Memory

In the code int *p1, p2;, only p1 is a pointer; p2 is a plain integer. To make both pointers, use int *p1, *p2;. This emphasizes that the modifier belongs to the individual declarator, not the base type.

TERMINAL bash — 80x24

> Ready. Click "Run" to execute.

QUESTION 1

Which of the following creates a reference correctly?

int &r;

int i = 10; int &r = i;

int &r = 10;

int *&r = &i;

QUESTION 2

In the declaration 'int* p1, p2;', what are the types of p1 and p2?

Both are pointers to int.

p1 is an int, p2 is a pointer to int.

p1 is a pointer to int, p2 is a plain int.

Neither are valid C++.

QUESTION 3

Which operator is used to obtain the memory address of an object?

The asterisk (*)

The ampersand (&)

The arrow (->)

The dot (.)

QUESTION 4

What is the result of dereferencing a pointer?

It gives the memory address.

It creates a new reference.

It yields the object to which the pointer points.

It clears the pointer's memory.

QUESTION 5

Which statement about references is FALSE?

A reference is not an object.

A reference can be null.

A reference must be initialized.

A reference cannot be redirected to a new object.

Module Assessment: Pointers, References, and Sales_data

Applying Compound Types and Structs

You are tasked with upgrading a legacy system. You must manage data using custom structures and ensure memory safety through correct pointer and reference usage.

Exercise 2.41: Based on the Sales_data struct (including bookNo, units_sold, and revenue), how would you rewrite a loop to read multiple transactions and update the total? Focus on the main function logic.

Solution:
To implement Exercise 2.41, define the Sales_data struct at the top of the file. In main(), declare a 'total' object. Use a while loop with 'std::cin >> total.bookNo >> total.units_sold >> price' where revenue is calculated as 'units_sold * price'. For subsequent entries, check if 'trans.bookNo == total.bookNo'. If true, update total.units_sold and total.revenue; if false, print the current total and reset it to the new transaction.

Consider the following snippet: 'int i = 42; int *p = &i; *p = *p * *p;'. Explain the final value of 'i' and the role of the asterisk in each part of the second line.

Solution:
The final value of 'i' is 1764 (42 squared). In '*p = *p * *p;', the first and second asterisks are dereference operators used to fetch and store values at the address held by p. The third asterisk is the multiplication operator. This demonstrates how pointers allow indirect modification of the original variable 'i'.