File I/O and Classes in C++
Chapter 12
1. What
capability does the fstream data type provide that the ifstream and ofstream
data type do not?
The fstream data type allows both
reading and writing, while the ifstream data type allows only for reading, and
the ofstream data type allows only for writing.
2. Which
file access flag do you use to open a file when you want all output written to
the end of the file’s existing contents?
ios::app
3. Assume that the file data.txt already exists, and the following statement executes. What happens to the file?
fstream file (“data.txt”, ios::out);
Its contents are erased. (In other words, the file is truncated.)
4. How do
you combine multiple file access flags when opening a file?
By using the | operator.
5. Should
file stream objects be passed to functions by value or by reference? Why?
By reference because the internal state
of file stream objects changes with most every operation. They should always be
passed to functions by reference to ensure internal consistency.
6. Under
what circumstances is a file stream object’s ios::hardfail bit set? What member
function reports the state of this bit?
When an unrecoverable error has
occurred.
7. Under
what circumstances is a file stream object’s ios::eofbit bit set? What member
function reports the state of this bit?
When the end of the file has been
encountered. The eof member function reports the state of this bit.
8. Under
what circumstances is a file stream object’s ios::badbit bit set? What member
function reports the state of this bit?
When an invalid operation has been
attempted.
9. How do
you read the contents of a text file that contains whitespace characters as
part of its data?
By using the getline member function.
10. What
arguments do you pass to a file stream object’s write member function?
Two arguments: The starting address of
the section of memory that is to be written to the file, and the number of
bytes that are to be written.
11. What
arguments do you pass to a file stream object’s read member function?
Two arguments: The starting address of
the section of memory where the data will be stored, and the number of bytes to
read.
12. What
type cast do you use to convert a pointer from one type to another?
reinterpret_cast
13. What is
the difference between the seekg and seekp member functions?
The seekg function moves a file’s write
position, and the seekp function moves a file’s read position.
14. How do
you get the byte number of a file’s current read position? How do you get the
byte number of a file’s current write position?
Use tellg to get the byte number of the
current read position and use tellp to get the byte number of the current write
position.
15. If a
program has read to the end of a file, what must you do before using either the
seekg or seekp member functions?
Call the file object’s clear member
function.
16. How do
you determine the number of bytes that a file contains?
First use the seekg member function to
move the read position to the last byte in the file. Then use the tellg
function to get the current byte number of the read position.
17. How do
you rewind a sequential-access file?
Use the seekg member function to move
the read position back to the beginning of the file.
18. The ____
file stream data type is for output files, input files, or files that perform
both input and output.
fstream
19. If a
files fails to open, the file stream object will be set to ____
0
20. The same
formatting techniques used with ____ may also be used when writing data to a
file.
cout
21. The ____
function reads a line of text from a file.
getline
22. The ____
member function reads a single character from a file.
get
23. The ____
member function writes a single character from a file.
put
24. ____
files contain data that is unformatted and not necessarily stored as ASCII
text.
Binary
25. ____
files contain data formatted as ____
Text, ASCII text
26. A(n)
____ is a complete set of data about a single item and is made up of ____
Record, fields
27. In C++,
____ provide a convenient way to organize data into fields and records.
Structures
28. The ____
member function writes “raw” binary data to a file.
write
29. The ____
member function reads “raw” binary data from a file.
read
30. The ____
operator is necessary if you pass anything other than a pointer-to-char as the
first argument of the two functions mentioned in questions 26 and 27.
Typecast
31. In ____
file access, the contents of the file are read in the order they appear in the
file, from the file’s start to its end.
Sequential
32. In ____
file access, the contents of a file may be read in any order.
Random
33. The ____
member function moves a file’s read position to a specified byte in the file.
seekg
34. The ____
member function moves a file’s write position to a specified byte in the file.
seekp
35. The ____
member function returns a file’s current read position.
tellg
36. The ____
member function returns a file’s current write position.
tellp
37. The ____
mode flag causes an offset to be calculated from the beginning of a file.
ios::beg
38. The ____
mode flag causes an offset to be calculated from the end of a file.
ios::end
39. The ____
mode flag causes an offset to be calculated from the current position in the
file.
ios::cur
40. A
negative offset causes the file’s read or write position to be moved ____ in
the file from the position specified by the mode.
Backward
41. Write a
statement that defines a file stream object named places. The object will be
used for both output and input.
fstream places (“places.dat”, ios::in |
ios::out);
42. Write two statements that use a file stream object named people to open a file named people.dat. (Show how to open the file with a member function and at the definition of the file stream object.) The file should be opened for output.
ofstream people (“people.dat”,
ios::out);
people.open (“people.dat”, ios::out);
43. Write two statements that use a file stream object named pets to open a file named pets.dat. (Show how to open the file with a member function and at the definition of the file stream object.) The file should be opened for input.
pets.open (“pets.dat”, ios::in);
fstream pets (“pets.dat”, ios::in);
44. Write two statements that use a file stream object named places to open a file named places.dat. (Show how to open the file with a member function and at the definition of the file stream object.) The file should be opened for both input and output.
fstream places (“places.dat”, ios::in
| ios::out);
places.open (“places.dat”, ios::in | ios::out);
45. Write a program segment that defines a file stream object named employees. The file should be opened for both input and output (in binary mode). If the file fails to open, the program segment should display an error message.
fstream employees;
employees.open (“emp.dat”, ios::in | ios::out | ios::binary);
if (!employees)
cout
46. Write code that opens the file data.txt for both input and output, but first determines if the file exists. If the file does not exist, the code should create it, then open it for both input and output.
fstream dataFile;
// Determine whether the file exists.
dataFile.open (“data.txt”, ios::in);
if (dataFile.fail () )
{
// The file does not exist, so
create it.
dataFile.open (“data.txt”,
ios::out);
dataFile.close();
}
// Now open the file for processing.
dataFile.open (“data.txt”, ios::in | ios::out);
47. Write code the determines the number of bytes contained in the file associated with the file stream object datafile.
dataFile.seekg (0L, ios::end);
numBytes = dataFile.tellg();
cout
48. The infoFile file stream object is used to sequentially access data. The program has already read to the end of the file. Write code that rewinds the file.
infoFile.clear();// Clear the eof
flag.
infoFile.seekg (0L, ios::beg);//
Rewind the read position.
49.
Different operating systems have different rules for naming files.
True
50. fstream
objects are only capable of performing file output operations.
False
51. ofstream
objects, by default, delete the contents of a file if it already exists when
opened.
True
52. ifstream
objects, by default, create a file if it doesn’t exist when opened.
False
53. Several
file access flags may be joined by using the | operator.
True
54. A file
may be opened in the definition of the file stream object.
True
55. A file
may be opened in the definition of the file stream object, no mode flags may be
specified.
False
56. A file
stream object’s fail member function may be used to determine if the file was
successfully opened.
True
57. The same
output formatting techniques used with cout may also be used with file stream
objects.
True
58. The
>> operator expects data to be delimited by whitespace characters.
True
59. The
getline member function can be used to read text that contains whitespaces.
True
60. It is
not possible to have more than one file open at once in a program.
False
61. Binary
files contain unformatted data, not necessarily stored as text.
True
62. Binary
is the default mode in which files are opened.
False
63. The
tellp member function tells a file stream object which byte to move its write
position to.
False
64. It is
possible to open a file for both input and output.
True
65. fstream
file (ios::in | ios::out);
file.open (“info.dat”);
if
(!file)
{
cout
}
File should be opened as:
fstream file (“info.dat”, ios:in | ios:out);
or
fstream file;
file.open (“info.dat”, ios::in | ios::out);
66. ofstream
file;
file.open (“info.dat”, ios::in);
if (file)
{
cout
}
Should not specify ios::in with an ofstream object. Also, the if statement should read: if (!file)
67. fstream
file (“info.dat”);
if (!file)
{
cout
}
File access flags must be specified with fstream objects.
68. fstream
dataFile (“info.dat”, ios::in | ios::binary);
int x;
datafile
The file access flags should be ios::in and ios::binary.
69. fstream
dataFile (“info.dat”, ios:in);
char stuff [81];
dataFile.get (stuff);
The file access flags should be ios::in. Also, the get member function cannot be used to read a string.
70. fstream
dataFile (“info.dat”, ios:in);
char stuff [81] =
“abcdefghijklmnopqrstuvwxyz”;
dataFile.put (stuff);
The file access flag should be ios::in. Also, the put member function cannot be used to write a string.
71. fstream
dataFile (“info.dat”, ios::out);
struct Date
{
int
month;
int day;
int year;
};
Date dt = { 4, 2, 98 };
dataFile.write (&dt, sizeof
(int));
The file access flag should be ios::out. Also, the last line should read: dataFile.write (reinterpret_cast (&dt), sizeof (dt));
72. fstream
inFile (“info.dat”, ios::in);
int x;
inFile.seekp (5);
inFile >> x;
The file access flag should be ios::in. Also, the seekp member function should not be used since the file is opened for input.
Chapter 13
1. What is
the difference between a class and an instance of the class?
A class describe a data type. An
instance of a class is an object of data type that exists in memory.
2. What is the difference between the following Person structure and Person class.
struct
Person
{
string name;
int age;
};
class Person
{
string name;
int age;
};
All members of a struct are public by default. The members of a class, however, are private by default.
3. What is
the default access specification of class members?
private
4. Look at the following function header for a member function.
void Circle::getRadius()
What is the
name of the function?
The function’s name is getRadius.
What class
is the function a member of?
It is a member of the Circle class.
5. A
contractor uses a blueprint to build a set of identical houses. Are classes
analogous to the blueprint or the houses?
A class is analogous to the blueprint.
6. What is a
mutator function? What is an accessor function?
A mutator is a member function that
stores a value in a private member variable, or in some way changes an
attribute. An accessor is a member function that retrieves the value stored in
a private member variable.
7. Is it a
good idea to make member variables private? Why or why not?
Yes it is. This protects the variables
from being directly manipulated by code outside the class, and prevents them
from receiving invalid data.
8. Can you
think of a good reason to avoid writing statements in a class member function
that use cout or cin?
Unless a class is specifically designed
to perform I/O, operations like user input and output are best left to the
person designing the application. Classes should provide member functions for
retrieving any important data without displaying them on the screen. Likewise,
they should provide member functions that store data into private member
variables without using cin. This allows a programmer to use the class without
being locked into a particular method of performing I/O.
9. Under
what circumstances should a member function be private?
When the function is necessary for
internal processing, but not useful to the program outside the class. In some
cases a class may contain member functions that initialize member variables or
destroy their contents. Those functions should not be accessible by an external
part of program because they may be called at the wrong time.
10. What is
a constructor? What is a destructor?
A constructor is a member function that
is automatically called when a class object is created. A destructor is a
member function that is automatically called when a class object is destroyed.
11. What is
a default constructor? Is it possible to have more than one default
constructor?
A default constructor is a constructor
that is called without any arguments. It is not possible to have more than one
constructor.
12. Is it
possible to have more than one constructor? Is it possible to have more than
one destructor?
Yes, it is possible to have more than
one constructor. It is not possible to have more than one destructor.
13. If a
class object is dynamically allocated in memory, does its constructor execute?
If so, when?
Yes, the constructor executes when the
object is created.
14. When
defining an array of class objects, how do you pass arguments to the
constructor for each object in the array?
You specify the arguments for each
object individually in an initialization list.
15. What are
a class’s responsibilities?
A class’s responsibilities are the
things that the class is responsible for knowing and the actions that the class
is responsible for doing.
16. How do
you identify the classes in a problem domain description?
Identify all the nouns (including
pronouns and noun phrases) in the problem domain description. Each of these is
a potential class. Then, refine the list to include only the classes that are
relevant to the problem.
17. The two
common programming methods in practice today are ____ and ____
Procedural programming, object-oriented
programming
18. ____
programming is centered around functions or procedures.
Procedural
19. ____
programming is centered around objects.
Object-oriented
20. ____ is
an object’s ability to contain and manipulate its own data.
Encapsulation
21. In C++
the ____ is the construct primarily used to create objects.
class
22. A class
is very similar to a(n) ____
Structure
23. A(n)
____ is a key word inside a class declaration that establishes a member’s
accessibility.
Access specifier
24. The
default access specification of class members is ____
private
25. The
default access specification of a struct in C++ is ____
public
26. Defining
a class object is often called the ____ of a class.
Instantiation
27. Members
of a class object may be accessed through a pointer to the object by using the
____ operator.
->
28. If you
were writing the declaration of a class named Canine, what would you name the
file it was stored in? ____
canine.h
29. If you
were writing the external definitions ofthe Canine class’s member functions, you would save them in a file named
____
canine.cpp
30. When a
member function’s body is written inside a class declaration, the function is
____
inline
31. A(n)
____ is automatically called when an object is created.
Constructor
32. A(n)
____ is a member function with the same name as the class.
Constructor
33. ____ are
useful for performing initialization or setup routines in a class object.
Constructors
34.
Constructors cannot have a(n) ____ type.
Return
35. A(n)
____ constructor is one that requires no arguments.
Default
36. A(n)
____ is a member function that is automatically called when an object is
destroyed.
Destructor
37. A
destructor has the same name as the class, but is preceded by a(n) ____
character.
~
38. Like
constructors, destructors cannot have a(n) ____ type.
Return
39. A
constructor whose arguments all have default values is a(n) ____ constructor.
Default
40. A class
may have than one constructor, as long as each has a different ____
Parameter list
41. A class
may only have one default ____ and one ____
Constructor, destructor
42. A(n)
____ may be used to pass arguments to the constructors of elements in an object
array.
Initialization list
43. Write a class declaration named Circle with a private member variable named radius. Write set and get functions to access the radius variable, and a function named getArea that returns the area of the circle. The area is calculated as: 3.14159 * radius * radius
class Circle
{
private;
double radius;
public;
void setRadius (double r)
{ radius = r; }
double getRadius()
{ return radius; }
double getArea()
{ return 3.14159 *
radius * radius; }
};
44. Add a default constructor to the Circle class in question 43. The constructor should initialize the radius member to 0.
class Circle
{
private:
double radius;
public:
Circle()
{ radius = 0.0; }
void setRadius (double r)
{ radius = r; }
double getRadius()
{ return radius; }
double getArea()
{ return 3.14159 *
radius * radius; }
};
45. Add an overloaded constructor to the Circle class in question 44. The constructor should accept an argument an assign its value to the radius member variable.
class Circle
{
private:
double radius;
public:
Circle()
{ radius = 0.0; }
Circle (double r)
{ radius = 0.0; }
void setRadius (double r)
{ radius = r; }
double getRadius()
{ return radius; }
double getArea()
{return 3.14159 *
radius * radius; }
};
46. Write a statement that defines an array of five objects of the Circle class in question 45. Let the default constructor execute for each element of the array.
const int SIZE = 5;
Circle collection [SIZE];
47. Write a statement that defines an array of five objects of the Circle class in question 45. Pass the following arguments to the elements’ constructor: 12, 7, 9, 14, and 8.
const int SIZE = 25;
Circle collection [SIZE] = {12, 7, 9, 14, 8 };
48. Write a for loop that displays the radius and area o the circles represented by the array you defined in question 47.
for (int i = 0; i
{
cout cout cout cout
}
49. If the items on the following list appeared in a problem domain description, which would be potential classes?
AnimalMedicationNurse
InoculateOperateAdvertise
DoctorInvoiceMeasure
PatientClientCustomer
The ones that would be potential classes are:
AnimalMedicationNurse
DoctorInvoiceCustomer
PatientClient
50. Look at the following description of a problem domain:
The bank offers the following types of accounts to its customers: savings accounts, checking accounts, and money market accounts. Customers are allowed to deposit money into an account (thereby increasing its balance), withdraw money from an account (thereby decreasing its balance), and earn interest on the account. Each account has an interest rate.
Assume that you are writing an application that will calculate the amount of interest earned for a bank account.
A) Identify
the potential classes in this problem domain.
B) Refine the list to include only the necessary class or classes for this
problem.
C) Identify the responsibilities of the class or classes.
A) After eliminating duplicates,
objects, and primitive values, the potential classes are: bank, account, and customer
B) The only class needed for this particular problem is account.
C) The account class knows its balance and interest rate.
The account can calculate interest
earned.
51. Private
members must be declared before public members.
False
52. Class
members are private by default.
True
53. Members
of a struct are private by default.
False
54. Classes
and structures in C++ are very similar.
True
55. All
private members of a class must be declared together.
False
56. All
public members of a class must be declared together.
False
57. It is
legal to define a pointer to a class object.
True
58. You can
use the new operator to dynamically allocate an instance of a class.
True
59. A
private member function may be called from a statement outside the class, as
long as the statement is in the same program as the class declaration.
False
60.
Constructors do not have to have the same name as the class.
False
61.
Constructors may not have a return type.
True
62.
Constructors cannot take arguments.
False
63.
Destructors cannot take arguments.
True
64.
Destructors may return a value.
False
65.
Constructors may have default arguments.
True
66. Member functions
may be overloaded.
True
67.
Constructors may not be overloaded.
False
68. A class
may not have a constructor with no parameter list, and a constructor whose
arguments all have default values.
True
69. A class
may only have one destructor.
True
70. When an
array of objects is defined, the constructor is only called for the first
element.
False
71. To find
the classes needed for an object-oriented application, you identify all of the
verbs in a description of the problem domain.
False
72. A
class’s responsibilities are the things the class is responsible for knowing,
and actions the class must perform.
True
73. class
Circle;
{
private
double
centerX;
double centerY;
double radius;
public
setCenter (double, double);
setRadius (double);
}
There should not be a colon after the
word Circle.
Colons should appear after the words private and public.
A semicolon should appear after the closing brace.
74. #include using namespace std;
Class Moon;
{
Private
double earthWeight;
double moonWeight;
Public
moonWeight (double ew);
{ earthWeight = ew;
moonWeight = earthWeight / 6; }
double getMoonWeight();
{ return moonWeight; }
}
int main()
{
double earth;
cout >> “What is your
weight? “;
cin Moon lunar (earth);
cout cout return 0;
}
The semicolon should not appear after
the word Moon.
The first character of the words private and public should not be capitalized.
There should be a colon, not a semicolon, following the words private and
public.
Semicolons should not appear in the member function headers.
In function main an argument is passed to a constructor that does not exist in
the Moon class.
The moonWeight member function should have been called prior to getMoonWeight.
75. #include
using namespace std;
class DumbBell;
{
int
weight;
public:
void setWeight (int);
};
void setWeight (int w)
{
weight = w;
}
int main()
{
DumbBell bar;
DumbBell (200);
cout return 0;
}
The semicolon should not appear after
the word DumbBell.
The function header for setWeight should appear as:
void DumbBell::setWeight (int w)
The line that reads:
DumbBell (200);
should read:
bar.setWeight (200);
bar.weight cannot be accessed outside
of the class because no access specifier appeared before it in the class,
making the variable private to the class by default.
This means the cout statement will not work.
76. class
Change
{
public:
int pennies;
int nickels;
int dimes;
int quarters;
Change()
{ pennies = nickels =
dimes = quarters = 0; }
Change (int p = 100, int n = 50,
d = 50, q =25);
};
void Change::Change (int p, int n, d, q)
{
pennies = p;
nickels = n;
dimes = d;
quarters = q;
}
Both constructors are considered the default constructor.
Short Answer Question
Compare text
file with binary file.
Binary file is a more secured file. Binary
file uses less data storage for the same amount of data to be stored.