Synapse india complain sharing info on chapter 8 operator overloading

1
Chapter 8 - Operator Overloading
Outline
8.1 Introduction
8.2 Fundamentals of Operator Overloading
8.3 Restrictions on Operator Overloading
8.4 Operator Functions as Class Members vs. as friend Functions
8.5 Overloading Stream-Insertion and Stream-Extraction Operators
8.6 Overloading Unary Operators
8.7 Overloading Binary Operators
8.8 Case Study: Array Class
8.9 Converting between Types
8.10 Case Study: A String Class
8.11 Overloading ++ and --
8.12 Case Study: A Date Class
8.13 Standard Library Classes string and vector

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8.1 Introduction
 Use operators with objects (operator
overloading)
- Clearer than function calls for certain classes
- Operator sensitive to context
 Examples
– <<
 Stream insertion, bitwise left-shift
– +
 Performs arithmetic on multiple types (integers, floats,
etc.)
 Will discuss when to use operator overloading

3
8.2 Fundamentals of Operator
Overloading
 Types
- Built in (int, char) or user-defined
- Can use existing operators with user-defined types
 Cannot create new operators
 Overloading operators
- Create a function for the class
- Name function operator followed by symbol
• Operator+ for the addition operator +

4
8.2 Fundamentals of Operator
Overloading
 Using operators on a class object
- It must be overloaded for that class
 Exceptions:
 Assignment operator, =
- Memberwise assignment between objects
 Address operator, &
- Returns address of object
 Both can be overloaded
 Overloading provides concise notation
– object2 = object1.add(object2);
– object2 = object2 + object1;

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8.3 Restrictions on Operator
Overloading
 Cannot change
- How operators act on built-in data types
 I.e., cannot change integer addition
- Precedence of operator (order of evaluation)
 Use parentheses to force order-of-operations
- Associativity (left-to-right or right-to-left)
- Number of operands
• & is unitary, only acts on one operand
 Cannot create new operators
 Operators must be overloaded explicitly
- Overloading + does not overload +=

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8.3 Restrictions on Operator
Overloading
Operators that can be overloaded
+ - * / % ^ & |
~ ! = < > += -= *=
/= %= ^= &= |= << >> >>=
<<= == != <= >= && || ++
-- ->* , -> [] () new delete
new[] delete[]
Operators that cannot be overloaded
. .* :: ?: sizeof

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8.4 Operator Functions As Class
Members Vs. As Friend Functions
 Operator functions
- Member functions
 Use this keyword to implicitly get argument
 Gets left operand for binary operators (like +)
 Leftmost object must be of same class as operator
- Non member functions
 Need parameters for both operands
 Can have object of different class than operator
 Must be a friend to access private or
protected data
- Called when
 Left operand of binary operator of same class
 Single operand of unitary operator of same class

8
 Overloaded << operator
- Left operand of type ostream &
 Such as cout object in cout << classObject
- Similarly, overloaded >> needs istream &
- Thus, both must be non-member functions

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 Commutative operators
- May want + to be commutative
 So both “a + b” and “b + a” work
- Suppose we have two different classes
- Overloaded operator can only be member function
when its class is on left
• HugeIntClass + Long int
 Can be member function
- When other way, need a non-member overload
function
• Long int + HugeIntClass

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8.5 Overloading Stream-Insertion and
Stream-Extraction Operators
• << and >>
- Already overloaded to process each built-in type
- Can also process a user-defined class
 Example program
- Class PhoneNumber
 Holds a telephone number
- Print out formatted number automatically
• (123) 456-7890

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fig08_03.cpp
(1 of 3)
1 // Fig. 8.3: fig08_03.cpp
2 // Overloading the stream-insertion
and
3 // stream-extraction operators.
4 #include <iostream>
5
Notice function prototypes for
overloaded operators >> and <<
They must be non-member friend
functions, since the object of class
Phonenumber appears on the right of
the operator.
cin << object
cout >> object
6 using std::cout;
7 using std::cin;
8 using std::endl;
9 using std::ostream;
10 using std::istream;
11
12 #include <iomanip>

The expression:
cout << phone;
is interpreted as the function call:
operator<<(cout, phone);
output is an alias for cout.
This allows objects to be cascaded.
cout << phone1 << phone2;
first calls
operator<<(cout, phone1), and
returns cout.
Next, cout << phone2 executes.
12
fig08_03.cpp
(2 of 3)
27
28 // overloaded stream-insertion
operator; cannot be
29 // a member function if we would
like to invoke it with
30 // cout << somePhoneNumber;
ignore() skips specified
number of characters from
31 ostream &operator<<( input (1 by default).
ostream
&output, const PhoneNumber &num )
32 {
Stream manipulator setw
restricts number of characters
read. setw(4) allows 3
characters to be read, leaving
room for the null character.
33 output << "(" <<
num.areaCode << ") "
34 << num.exchange << "-"

13
fig08_03.cpp
(3 of 3)
fig08_03.cpp
output (1 of 1)
53
54 } // end function operator>>
55
56 int main()
57 {
58 PhoneNumber phone; // create
object phone
59
Enter phone number in the form (123) 456-7890:
(800) 555-1212
The phone number entered was: (800) 555-1212
60 cout << "Enter phone number
in the form (123) 456-7890:n";
61
62 // cin >> phone invokes

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 Overloading unary operators
- Non-static member function, no arguments
- Non-member function, one argument
 Argument must be class object or reference to class
object
- Remember, static functions only access static
data

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 Upcoming example (8.10)
- Overload ! to test for empty string
- If non-static member function, needs no
arguments
• !s becomes s.operator!()
class String {
public:
bool operator!() const;
...
};
- If non-member function, needs one argument
• s! becomes operator!(s)
class String {
friend bool operator!( const String & )
...
}

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 Overloading binary operators
- Non-static member function, one argument
- Non-member function, two arguments
 One argument must be class object or reference
 Upcoming example
- If non-static member function, needs one
argument
class String {
public:
const String &operator+=( const String & );
...
};
– y += z equivalent to y.operator+=( z )

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 Upcoming example
- If non-member function, needs two arguments
- Example:
class String {
friend const String &operator+=(
String &, const String & );
...
};
– y += z equivalent to operator+=( y, z )

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8.8 Case Study: Array class
 Arrays in C++
- No range checking
- Cannot be compared meaningfully with ==
- No array assignment (array names const pointers)
- Cannot input/output entire arrays at once
 One element at a time
 Example:Implement an Array class with
- Range checking
- Array assignment
- Arrays that know their size
- Outputting/inputting entire arrays with << and >>
- Array comparisons with == and !=

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8.8 Case Study: Array class
 Copy constructor
- Used whenever copy of object needed
 Passing by value (return value or parameter)
 Initializing an object with a copy of another
– Array newArray( oldArray );
– newArray copy of oldArray
- Prototype for class Array
• Array( const Array & );
 Must take reference
- Otherwise, pass by value
- Tries to make copy by calling copy constructor…
- Infinite loop

array1.h (1 of 2)
20
1 // Fig. 8.4: array1.h
2 // Array class for storing arrays
of integers.
3 #ifndef ARRAY1_H
4 #define ARRAY1_H
5
Most operators overloaded as
member functions (except <<
and >>, which must be non-member
7
functions).
10
Prototype for copy constructor.
11 class Array {
12 friend ostream

array1.h (2 of 2)
21
27 // inequality operator; returns
opposite of == operator
28 bool operator!=( const Array
&right ) const
!= operator simply returns
opposite of == operator.
Thus, only need to define the
== operator.
29 {
30 return ! ( *this == right ); //
invokes Array::operator==
31
32 } // end function operator!=
33
34 // subscript operator for non-const

array1.cpp (1 of 7)
22
1 // Fig 8.5: array1.cpp
2 // Member function definitions for
class Array
4
5 using std::cout;
6 using std::cin;
7 using std::endl;
8
10
11 using std::setw;
12

array1.cpp (2 of 7)
23
27 for ( int i = 0; i < size; i++ )
28 ptr[ i ] = 0; // initialize
array
29
We must declare a new integer array so
the objects do not point to the same
memory.
30 } // end Array default constructor
31
32 // copy constructor for class
Array;
33 // must receive a reference to
prevent infinite recursion
34 Array::Array( const Array
&arrayToCopy )
35 : size( arrayToCopy.size )
36 {

array1.cpp (3 of 7)
24
51 // return size of array
52 int Array::getSize() const
53 {
Want to avoid self-assignment.
54 return size;
55
56 } // end function getSize
57
58 // overloaded assignment
operator;
59 // const return avoids: ( a1 = a2 )
= a3
60 const Array
&Array::operator=( const Array
&right )

array1.cpp (4 of 7)
25
77
78 return *this; // enables x = y =
z, for example
79
80 } // end function operator=
81
82 // determine if two arrays are
equal and
83 // return true, otherwise return
false
84 bool Array::operator==( const
Array &right ) const
85 {
86 if ( size != right.size )

array1.cpp (5 of 7)
26
98 // overloaded subscript operator
for non-const Arrays
99 // reference return creates an
lvalue
integers1[5] calls
integers1.operator[]( 5 )
100 int &Array::operator[]( int
exit() (header <cstdlib>) ends
the program.
subscript )
101 {
102 // check for subscript out of
range error
103 if ( subscript < 0 || subscript >=
size ) {
104 cout << "nError: Subscript "
<< subscript
105 << " out of range" <<

array1.cpp (6 of 7)
27
115 // overloaded subscript operator
for const Arrays
116 // const reference return creates
an rvalue
117 const int &Array::operator[]( int
subscript ) const
118 {
119 // check for subscript out of
range error
size ) {
121 cout << "nError: Subscript "
<< subscript

array1.cpp (7 of 7)
28
142
143 // overloaded output operator for
class Array
144 ostream &operator<<( ostream
&output, const Array &a )
145 {
146 int i;
147
148 // output private ptr-based
array
149 for ( i = 0; i < a.size; i++ ) {
150 output << setw( 12 ) << a.ptr[
i ];
151

29
fig08_06.cpp
(1 of 3)
1 // Fig. 8.6: fig08_06.cpp
2 // Array class test program.
4
5 using std::cout;
6 using std::cin;
7 using std::endl;
8
9 #include "array1.h"
10
11 int main()
12 {
13 Array integers1( 7 ); // seven-element

30
fig08_06.cpp
(2 of 3)
26 // input and print integers1 and
integers2
27 cout << "nInput 17
integers:n";
28 cin >> integers1 >> integers2;
29
30 cout << "nAfter input, the
arrays contain:n"
31 << "integers1:n" <<
integers1
integers2;
33
34 // use overloaded inequality (!

31
fig08_06.cpp
(3 of 3)
48 // use overloaded assignment
(=) operator
49 cout << "nAssigning integers2
to integers1:n";
50 integers1 = integers2; // note
target is smaller
51
52 cout << "integers1:n" <<
integers1
integers2;
54
55 // use overloaded equality (==)
operator

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fig08_06.cpp
output (1 of 3)
Size of array integers1 is 7
Array after initialization:
0 0 0 0
0 0 0
0 0 0 0
0 0 0 0
0 0
Input 17 integers:

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fig08_06.cpp
output (2 of 3)
Evaluating: integers1 != integers2
integers1 and integers2 are not equal
1 2 3 4
5 6 7
Assigning integers2 to integers1:
integers1:
8 9 10 11
12 13 14 15
16 17

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fig08_06.cpp
output (3 of 3)
Assigning 1000 to integers1[5]
integers1:
8 9 10 11
12 1000 14 15
16 17
Attempt to assign 1000 to
integers1[15]
Error: Subscript 15 out of range

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 Casting
- Traditionally, cast integers to floats, etc.
- May need to convert between user-defined types
 Cast operator (conversion operator)
- Convert from
 One class to another
 Class to built-in type (int, char, etc.)
- Must be non-static member function
 Cannot be friend
- Do not specify return type
 Implicitly returns type to which you are converting

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 Example
- Prototype
A::operator char *() const;
 Casts class A to a temporary char *
• (char *)s calls s.operator char*()
- Also
• A::operator int() const;
• A::operator OtherClass() const;

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 Casting can prevent need for overloading
- Suppose class String can be cast to char *
– cout << s; // s is a String
• Compiler implicitly converts s to char *
• Do not have to overload <<
- Compiler can only do 1 cast

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8.10 Case Study: A String Class
 Build class String
- String creation, manipulation
- Class string in standard library (more Chapter
15)
 Conversion constructor
- Single-argument constructor
- Turns objects of other types into class objects
• String s1(“hi”);
 Creates a String from a char *
- Any single-argument constructor is a conversion
constructor

string1.h (1 of 3)
39
1 // Fig. 8.7: string1.h
2 // String class definition.
3 #ifndef STRING1_H
4 #define STRING1_H
5
Conversion constructor to
make a String from a char
*.
7
s1 += s2 interpreted as
s1.operator+=(s2)
Can also concatenate a String
and a char * because the
compiler will cast the char *
argument to a String.
However, it can only do 1 level
of casting.
10
11 class String {
12 friend ostream
&operator<<( ostream &, const String

string1.h (2 of 3)
40
27 // test s1 != s2
28 bool operator!=( const String &
right ) const
29 {
30 return !( *this == right );
31
32 } // end function operator!=
33
34 // test s1 > s2
35 bool operator>( const String
&right ) const

string1.h (3 of 3)
41
54
Two overloaded subscript
operators, for const and
non-const objects.
55 char &operator[]
( int ); // subscript operator
56 const char &operator[]( int )
Overload the function call
operator () to return a
substring. This operator can
have any amount of operands.
const; // subscript operator
57
58 String operator()( int,
int ); // return a substring
59
60 int getLength()
const; // return string length
61
62 private:
63 int length; // string length

string1.cpp (1 of 8)
42
1 // Fig. 8.8: string1.cpp
2 // Member function definitions for
class String.
4
5 using std::cout;
6 using std::endl;
7
9
10 using std::setw;
11
12 #include <new> // C++

43
27
28 // copy constructor
29 String::String( const String
&copy )
30 : length( copy.length )
31 {
32 cout << "Copy constructor: "
<< copy.sPtr << 'n';
33 setString( copy.sPtr ); // call
utility function
34
35 } // end String copy constructor
36

44
55
56 else
57 cout << "Attempted
assignment of a String to itselfn";
58
59 return *this; // enables
cascaded assignments
60
61 } // end function operator=
62
63 // concatenate right operand to
this object and
64 // store in this object.

45
81 // is this String empty?
82 bool String::operator!() const
83 {
84 return length == 0;
85
86 } // end function operator!
87
88 // is this String equal to right
String?
89 bool String::operator==( const
String &right ) const
90 {
91 return strcmp( sPtr, right.sPtr )

46
102 // return reference to character
in String as lvalue
103 char &String::operator[]( int
subscript )
104 {
105 // test for subscript out of
range
length ) {
107 cout << "Error: Subscript "
<< subscript
endl;
109

47
131
132 // return a substring beginning at
index and
133 // of length subLength
134 String String::operator()( int
index, int subLength )
135 {
136 // if index is out of range or
substring length < 0,
137 // return an empty String object
138 if ( index < 0 || index >= length
|| subLength < 0 )
139 return ""; // converted to a
String object automatically

48
156
157 // create temporary String
object containing the substring
158 String tempString( tempPtr );
159 delete [] tempPtr; // delete
temporary array
160
161 return tempString; // return
copy of the temporary String
162
163 } // end function operator()
164
165 // return string length

49
179
180 // overloaded output operator
&output, const String &s )
182 {
183 output << s.sPtr;
184
185 return output; // enables
cascading
186
187 } // end function operator<<
188
189 // overloaded input operator

50
fig08_09.cpp
(1 of 4)
1 // Fig. 8.9: fig08_09.cpp
2 // String class test program.
4
5 using std::cout;
6 using std::endl;
7
8 #include "string1.h"
9
10 int main()
11 {
12 String s1( "happy" );
13 String s2( " birthday" );

51
fig08_09.cpp
(2 of 4)
26 << "ns2 < s1 yields "
27 << ( s2 < s1 ? "true" :
"false" )
28 << "ns2 >= s1 yields "
29 << ( s2 >= s1 ? "true" :
"false" )
30 << "ns2 <= s1 yields "
31 << ( s2 <= s1 ? "true" :
"false" );
32
33 // test overloaded String empty
(!) operator
34 cout << "nnTesting !s3:n";
35

52
fig08_09.cpp
(3 of 4)
51
52 // test overloaded function call
operator () for substring
53 cout << "The substring of s1
starting atn"
54 << "location 0 for 14
characters, s1(0, 14), is:n"
55 << s1( 0, 14 ) << "nn";
56
57 // test substring "to-end-of-
String" option
starting atn"
59 << "location 15, s1(15, 0),

53
fig08_09.cpp
(4 of 4)
74 // test using subscript operator
to create lvalue
75 s1[ 0 ] = 'H';
76 s1[ 6 ] = 'B';
77 cout << "ns1 after s1[0] = 'H'
and s1[6] = 'B' is: "
78 << s1 << "nn";
79
80 // test subscript out of range
81 cout << "Attempt to assign 'd'

54
fig08_09.cpp
(1 of 3)
Conversion constructor: happy
Conversion constructor: birthday
Conversion constructor:
s1 is "happy"; s2 is " birthday"; s3 is
""
The results of comparing s2 and s1:
s2 == s1 yields false
s2 != s1 yields true
s2 > s1 yields false
s2 < s1 yields true
s2 >= s1 yields false
s2 <= s1 yields true
The constructor and
destructor are called for the
temporary String
(converted from the char *
“to you”).

55
fig08_09.cpp
(2 of 3)
Conversion constructor: happy
birthday
Copy constructor: happy birthday
Destructor: happy birthday
The substring of s1 starting at
location 0 for 14 characters, s1(0,
14), is:
happy birthday
Destructor: happy birthday
Conversion constructor: to you
Copy constructor: to you
Destructor: to you

56
fig08_09.cpp
(3 of 3)
s1 after s1[0] = 'H' and s1[6] = 'B' is:
Happy Birthday to you
Attempt to assign 'd' to s1[30] yields:
Error: Subscript 30 out of range

57
 Increment/decrement operators can be
overloaded
- Add 1 to a Date object, d1
- Prototype (member function)
• Date &operator++();
• ++d1 same as d1.operator++()
- Prototype (non-member)
• Friend Date &operator++( Date &);
• ++d1 same as operator++( d1 )

58
 To distinguish pre/post increment
- Post increment has a dummy parameter
• int of 0
- Prototype (member function)
• Date operator++( int );
• d1++ same as d1.operator++( 0 )
- Prototype (non-member)
• friend Date operator++( Data &, int );
• d1++ same as operator++( d1, 0 )
- Integer parameter does not have a name
 Not even in function definition

59
 Return values
- Preincrement
 Returns by reference (Date &)
 lvalue (can be assigned)
- Postincrement
 Returns by value
 Returns temporary object with old value
 rvalue (cannot be on left side of assignment)
 Decrement operator analogous

60
8.12 Case Study: A Date Class
 Example Date class
- Overloaded increment operator
 Change day, month and year
- Overloaded += operator
- Function to test for leap years
- Function to determine if day is last of month

61
date1.h (1 of 2)
1 // Fig. 8.10: date1.h
2 // Date class definition.
3 #ifndef DATE1_H
4 #define DATE1_H
6
8
9 class Date {
10 friend ostream
&operator<<( ostream &, const Date
& );
11
Note difference between pre
and post increment.

62
date1.h (2 of 2)
23
24 private:
25 int month;
26 int day;
27 int year;
28
29 static const int days[]; //
array of days per month
30 void helpIncrement(); //
utility function
31
32 }; // end class Date
33

date1.cpp (1 of 5)
63
1 // Fig. 8.11: date1.cpp
2 // Date class member function
definitions.
4 #include "date1.h"
5
6 // initialize static member at file
scope;
7 // one class-wide copy
8 const int Date::days[] =
9 { 0, 31, 28, 31, 30, 31, 30, 31,
31, 30, 31, 30, 31 };
10

date1.cpp (2 of 5)
64
24 // test for a leap year
25 if ( month == 2 &&
leapYear( year ) )
26 day = ( dd >= 1 && dd <=
29 ) ? dd : 1;
27 else
28 day = ( dd >= 1 && dd <=
Postincrement updates object
and returns a copy of the
original. Do not return a
reference to temp, because it
is a local variable that will be
destroyed.
Also note that the integer
parameter does not have a
name.
days[ month ] ) ? dd : 1;
29
30 } // end function setDate
31
32 // overloaded preincrement
operator
33 Date &Date::operator++()

date1.cpp (3 of 5)
65
52
53 // add specified number of days
to date
54 const Date
&Date::operator+=( int additionalDays
)
55 {
56 for ( int i = 0; i <
additionalDays; i++ )
57 helpIncrement();
58
59 return *this; // enables
cascading
60

date1.cpp (4 of 5)
66
75 // determine whether the day is
the last day of the month
76 bool Date::endOfMonth( int
testDay ) const
77 {
78 if ( month == 2 &&
leapYear( year ) )
79 return testDay == 29; // last
day of Feb. in leap year
80 else
81 return testDay ==
days[ month ];
82
83 } // end function endOfMonth

date1.cpp (5 of 5)
67
100 // last day of year
101 else {
102 ++year;
103 month = 1;
104 day = 1;
105 }
106
107 } // end function helpIncrement
108
109 // overloaded output operator
&output, const Date &d )
111 {

68
fig08_12.cpp
(1 of 2)
1 // Fig. 8.12: fig08_12.cpp
2 // Date class test program.
4
5 using std::cout;
6 using std::endl;
7
8 #include "date1.h" // Date class
definition
9
10 int main()
11 {
12 Date d1; // defaults to January

69
fig08_12.cpp
(2 of 2)
26
27 cout << "nnTesting the
preincrement operator:n"
28 << " d4 is " << d4 << 'n';
29 cout << "++d4 is " << ++d4 <<
'n';
30 cout << " d4 is " << d4;
31
32 cout << "nnTesting the
postincrement operator:n"
33 << " d4 is " << d4 << 'n';

70
fig08_12.cpp
output (1 of 1)
d1 is January 1, 1900
d2 is December 27, 1992
d3 is January 1, 1900
d2 += 7 is January 3, 1993
d3 is February 28, 1992
++d3 is February 29, 1992
Testing the preincrement operator:
d4 is July 13, 2002
++d4 is July 14, 2002
d4 is July 14, 2002

71
8.13Standard Library Classes
string and vector
 Classes built into C++
- Available for anyone to use
– string
 Similar to our String class
– vector
 Dynamically resizable array
 Redo our String and Array examples
- Use string and vector

72
string and vector
 Class string
- Header <string>, namespace std
- Can initialize string s1(“hi”);
- Overloaded <<
• cout << s1
- Overloaded relational operators
• == != >= > <= <
- Assignment operator =
- Concatenation (overloaded +=)

73
string and vector
 Class string
- Substring function substr
• s1.substr(0, 14);
- Starts at location 0, gets 14 characters
• S1.substr(15)
- Substring beginning at location 15
- Overloaded []
 Access one character
 No range checking (if subscript invalid)
– at function
• s1.at(10)
 Character at subscript 10
 Has bounds checking
- Will end program if invalid (learn more in Chapter 13)

74
fig08_13.cpp
(1 of 4)
1 // Fig. 8.13: fig08_13.cpp
2 // Standard library string class
test program.
4
5 using std::cout;
6 using std::endl;
7
8 #include <string>
9
10 using std::string;
11
12 int main()

75
fig08_13.cpp
(2 of 4)
26 << "ns2 > s1 yields "
27 << ( s2 > s1 ? "true" :
"false" )
28 << "ns2 < s1 yields "
29 << ( s2 < s1 ? "true" :
"false" )
30 << "ns2 >= s1 yields "
31 << ( s2 >= s1 ? "true" :
"false" )
32 << "ns2 <= s1 yields "
33 << ( s2 <= s1 ? "true" :
"false" );
34
35 // test string member function

76
fig08_13.cpp
(3 of 4)
49 // test overloaded string
concatenation operator
50 // with C-style string
51 cout << "nns1 += " to you"
yieldsn";
52 s1 += " to you";
53 cout << "s1 = " << s1 << "nn";
54
55 // test string member function
substr
starting at location 0 forn"
57 << "14 characters,
s1.substr(0, 14), is:n"

77
fig08_13.cpp
(4 of 4)
74 // test destructor
75 delete s4Ptr;
76
77 // test using subscript operator
to create lvalue
78 s1[ 0 ] = 'H';
79 s1[ 6 ] = 'B';
80 cout << "ns1 after s1[0] = 'H'
and s1[6] = 'B' is: "
81 << s1 << "nn";
82
83 // test subscript out of range
with string member function "at"

78
fig08_13.cpp
output (1 of 2)
s1 is "happy"; s2 is " birthday"; s3 is
""
The results of comparing s2 and s1:
s2 == s1 yields false
s2 != s1 yields true
s2 > s1 yields false
s2 < s1 yields true
s2 >= s1 yields false
s2 <= s1 yields true
Testing s3.empty():
s3 is empty; assigning s1 to s3;

79
fig08_13.cpp
output (2 of 2)
The substring of s1 starting at
location 15, s1.substr(15), is:
to you
*s4Ptr = happy birthday to you
assigning *s4Ptr to *s4Ptr
*s4Ptr = happy birthday to you
s1 after s1[0] = 'H' and s1[6] = 'B' is:
Happy Birthday to you
Attempt to assign 'd' to s1.at( 30 )

80
string and vector
 Class vector
- Header <vector>, namespace std
- Store any type
• vector< int > myArray(10)
- Function size ( myArray.size() )
- Overloaded []
 Get specific element, myArray[3]
- Overloaded !=, ==, and =
 Inequality, equality, assignment

81
fig08_14.cpp
(1 of 5)
1 // Fig. 8.14: fig08_14.cpp
2 // Demonstrating standard library
class vector.
4
5 using std::cout;
6 using std::cin;
7 using std::endl;
8
10
11 using std::setw;
12

82
fig08_14.cpp
(2 of 5)
25 // print integers1 size and
contents
26 cout << "Size of vector
integers1 is "
27 << integers1.size()
28 << "nvector after
initialization:n";
29 outputVector( integers1 );
30
31 // print integers2 size and
contents
32 cout << "nSize of vector
integers2 is "
33 << integers2.size()

83
fig08_14.cpp
(3 of 5)
51 if ( integers1 != integers2 )
52 cout << "integers1 and
integers2 are not equaln";
53
54 // create vector integers3 using
integers1 as an
55 // initializer; print size and
contents
56 vector< int >
integers3( integers1 ); // copy
constructor
57
58 cout << "nSize of vector
integers3 is "

84
fig08_14.cpp
(4 of 5)
73 // use overloaded equality (==)
operator
74 cout << "nEvaluating:
integers1 == integers2n";
75
76 if ( integers1 == integers2 )
77 cout << "integers1 and
integers2 are equaln";
78
79 // use overloaded subscript
operator to create rvalue
80 cout << "nintegers1[5] is " <<
integers1[ 5 ];
81

85
fig08_14.cpp
(5 of 5)
97 // output vector contents
98 void outputVector( const vector<
int > &array )
99 {
100 for ( int i = 0; i < array.size(); i+
+ ) {
101 cout << setw( 12 ) << array[ i
];
102
103 if ( ( i + 1 ) % 4 == 0 ) // 4
numbers per row of output
104 cout << endl;
105
106 } // end for

86
fig08_14.cpp
output (1 of 2)
Size of vector integers1 is 7
vector after initialization:
0 0 0 0
0 0 0
0 0 0 0
0 0 0 0
0 0
Input 17 integers:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

87
fig08_14.cpp
output (2 of 2)
1 2 3 4
5 6 7
Assigning integers2 to integers1:
integers1:
8 9 10 11
12 13 14 15
16 17
integers2:
8 9 10 11
12 13 14 15

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