Operator overloading

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

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

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 +

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;

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 +=

8. 3 Restrictions on Operator Overloading

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

8.4 Operator Functions As Class Members Vs. As Friend Functions 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

8.4 Operator Functions As Class Members Vs. As Friend Functions 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

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

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 6 using std::cout; 7 using std::cin; 8 using std::endl; 9 using std::ostream; 10 using std::istream; 11 12 #include <iomanip> 13 14 using std::setw; 15 16 // PhoneNumber class definition 17 class PhoneNumber { 18 friend ostream & operator <<( ostream&, const PhoneNumber & ); 19 friend istream & operator >>( istream&, PhoneNumber & ); 20 21 private : 22 char areaCode[ 4 ]; // 3-digit area code and null 23 char exchange[ 4 ]; // 3-digit exchange and null 24 char line[ 5 ]; // 4-digit line and null 25 26 }; // end class PhoneNumber 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

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; 31 ostream & operator <<( ostream &output, const PhoneNumber &num ) 32 { 33 output << "(" << num.areaCode << ") " 34 << num.exchange << "-" << num.line; 35 36 return output; // enables cout << a << b << c; 37 38 } // end function operator<< 39 40 // overloaded stream-extraction operator; cannot be 41 // a member function if we would like to invoke it with 42 // cin >> somePhoneNumber; 43 istream & operator >>( istream &input, PhoneNumber &num ) 44 { 45 input.ignore(); // skip ( 46 input >> setw( 4 ) >> num.areaCode; // input area code 47 input.ignore( 2 ); // skip ) and space 48 input >> setw( 4 ) >> num.exchange; // input exchange 49 input.ignore(); // skip dash (-) 50 input >> setw( 5 ) >> num.line; // input line 51 52 return input; // enables cin >> a >> b >> c; 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. ignore() skips specified number of characters from input (1 by default). Stream manipulator setw restricts number of characters read. setw(4) allows 3 characters to be read, leaving room for the null character.

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 60 cout << "Enter phone number in the form (123) 456-7890:\n" ; 61 62 // cin >> phone invokes operator>> by implicitly issuing 63 // the non-member function call operator>>( cin, phone ) 64 cin >> phone; 65 66 cout << "The phone number entered was: " ; 67 68 // cout << phone invokes operator<< by implicitly issuing 69 // the non-member function call operator<<( cout, phone ) 70 cout << phone << endl; 71 72 return 0 ; 73 74 } // end main Enter phone number in the form (123) 456-7890: (800) 555-1212 The phone number entered was: (800) 555-1212

8.6 Overloading Unary Operators 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

8.6 Overloading Unary Operators 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 & ) ... }

8.7 Overloading Binary Operators 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 )

8.7 Overloading Binary Operators 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 )

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 !=

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) 1 // Fig. 8.4: array1.h 2 // Array class for storing arrays of integers. 3 #ifndef ARRAY1_H 4 #define ARRAY1_H 5 6 #include <iostream> 7 8 using std::ostream; 9 using std::istream; 10 11 class Array { 12 friend ostream & operator <<( ostream &, const Array & ); 13 friend istream & operator >>( istream &, Array & ); 14 15 public : 16 Array( int = 10 ); // default constructor 17 Array( const Array & ); // copy constructor 18 ~Array(); // destructor 19 int getSize() const ; // return size 20 21 // assignment operator 22 const Array & operator =( const Array & ); 23 24 // equality operator 25 bool operator ==( const Array & ) const ; 26 Most operators overloaded as member functions (except << and >> , which must be non-member functions). Prototype for copy constructor.

array1.h (2 of 2) 27 // inequality operator; returns opposite of == operator 28 bool operator !=( const Array &right ) const 29 { 30 return ! ( * this == right ); // invokes Array::operator== 31 32 } // end function operator!= 33 34 // subscript operator for non-const objects returns lvalue 35 int & operator []( int ); 36 37 // subscript operator for const objects returns rvalue 38 const int & operator []( int ) const ; 39 40 private : 41 int size; // array size 42 int *ptr; // pointer to first element of array 43 44 }; // end class Array 45 46 #endif != operator simply returns opposite of == operator. Thus, only need to define the == operator.

array1.cpp (1 of 7) 1 // Fig 8.5: array1.cpp 2 // Member function definitions for class Array 3 #include <iostream> 4 5 using std::cout; 6 using std::cin; 7 using std::endl; 8 9 #include <iomanip> 10 11 using std::setw; 12 13 #include <new> // C++ standard "new" operator 14 15 #include <cstdlib> // exit function prototype 16 17 #include "array1.h" // Array class definition 18 19 // default constructor for class Array (default size 10) 20 Array::Array( int arraySize ) 21 { 22 // validate arraySize 23 size = ( arraySize > 0 ? arraySize : 10 ); 24 25 ptr = new int[ size ]; // create space for array 26

array1.cpp (2 of 7) 27 for ( int i = 0 ; i < size; i++ ) 28 ptr[ i ] = 0 ; // initialize array 29 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 { 37 ptr = new int[ size ]; // create space for array 38 39 for ( int i = 0 ; i < size; i++ ) 40 ptr[ i ] = arrayToCopy.ptr[ i ]; // copy into object 41 42 } // end Array copy constructor 43 44 // destructor for class Array 45 Array::~Array() 46 { 47 delete [] ptr; // reclaim array space 48 49 } // end destructor 50 We must declare a new integer array so the objects do not point to the same memory.

array1.cpp (3 of 7) 51 // return size of array 52 int Array::getSize() const 53 { 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 ) 61 { 62 if ( &right != this ) { // check for self-assignment 63 64 // for arrays of different sizes, deallocate original 65 // left-side array, then allocate new left-side array 66 if ( size != right.size ) { 67 delete [] ptr; // reclaim space 68 size = right.size; // resize this object 69 ptr = new int [ size ]; // create space for array copy 70 71 } // end inner if 72 73 for ( int i = 0 ; i < size; i++ ) 74 ptr[ i ] = right.ptr[ i ]; // copy array into object 75 76 } // end outer if Want to avoid self-assignment.

array1.cpp (4 of 7) 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 ) 87 return false ; // arrays of different sizes 88 89 for ( int i = 0 ; i < size; i++ ) 90 91 if ( ptr[ i ] != right.ptr[ i ] ) 92 return false ; // arrays are not equal 93 94 return true ; // arrays are equal 95 96 } // end function operator== 97

array1.cpp (5 of 7) 98 // overloaded subscript operator for non-const Arrays 99 // reference return creates an lvalue 100 int &Array:: operator []( int 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" << endl; 106 107 exit( 1 ); // terminate program; subscript out of range 108 109 } // end if 110 111 return ptr[ subscript ]; // reference return 112 113 } // end function operator[] 114 integers1[5] calls integers1.operator[]( 5 ) exit() (header <cstdlib> ) ends the program.

array1.cpp (6 of 7) 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 120 if ( subscript < 0 || subscript >= size ) { 121 cout << "\nError: Subscript " << subscript 122 << " out of range" << endl; 123 124 exit( 1 ); // terminate program; subscript out of range 125 126 } // end if 127 128 return ptr[ subscript ]; // const reference return 129 130 } // end function operator[] 131 132 // overloaded input operator for class Array; 133 // inputs values for entire array 134 istream & operator >>( istream &input, Array &a ) 135 { 136 for ( int i = 0 ; i < a.size; i++ ) 137 input >> a.ptr[ i ]; 138 139 return input; // enables cin >> x >> y; 140 141 } // end function

array1.cpp (7 of 7) 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 ]; 151 152 if ( ( i + 1 ) % 4 == 0 ) // 4 numbers per row of output 153 output << endl; 154 155 } // end for 156 157 if ( i % 4 != 0 ) // end last line of output 158 output << endl; 159 160 return output; // enables cout << x << y; 161 162 } // end function operator<<

fig08_06.cpp (1 of 3) 1 // Fig. 8.6: fig08_06.cpp 2 // Array class test program. 3 #include <iostream> 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 Array 14 Array integers2; // 10-element Array by default 15 16 // print integers1 size and contents 17 cout << "Size of array integers1 is " 18 << integers1.getSize() 19 << "\nArray after initialization:\n" << integers1; 20 21 // print integers2 size and contents 22 cout << "\nSize of array integers2 is " 23 << integers2.getSize() 24 << "\nArray after initialization:\n" << integers2; 25

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 32 << "integers2:\n" << integers2; 33 34 // use overloaded inequality (!=) operator 35 cout << "\nEvaluating: integers1 != integers2\n" ; 36 37 if ( integers1 != integers2 ) 38 cout << "integers1 and integers2 are not equal\n" ; 39 40 // create array integers3 using integers1 as an 41 // initializer; print size and contents 42 Array integers3( integers1 ); // calls copy constructor 43 44 cout << "\nSize of array integers3 is " 45 << integers3.getSize() 46 << "\nArray after initialization:\n" << integers3; 47

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 53 << "integers2:\n" << integers2; 54 55 // use overloaded equality (==) operator 56 cout << "\nEvaluating: integers1 == integers2\n" ; 57 58 if ( integers1 == integers2 ) 59 cout << "integers1 and integers2 are equal\n" ; 60 61 // use overloaded subscript operator to create rvalue 62 cout << "\nintegers1[5] is " << integers1[ 5 ]; 63 64 // use overloaded subscript operator to create lvalue 65 cout << "\n\nAssigning 1000 to integers1[5]\n" ; 66 integers1[ 5 ] = 1000 ; 67 cout << "integers1:\n" << integers1; 68 69 // attempt to use out-of-range subscript 70 cout << "\nAttempt to assign 1000 to integers1[15]" << endl; 71 integers1[ 15 ] = 1000; // ERROR: out of range 72 73 return 0 ; 74 75 } // end main

fig08_06.cpp output (1 of 3) Size of array integers1 is 7 Array after initialization: 0 0 0 0 0 0 0 Size of array integers2 is 10 Array after initialization: 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 16 17 After input, the arrays contain: integers1: 1 2 3 4 5 6 7 integers2: 8 9 10 11 12 13 14 15

fig08_06.cpp output (2 of 3) Evaluating: integers1 != integers2 integers1 and integers2 are not equal Size of array integers3 is 7 Array after initialization: 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 16 17 Evaluating: integers1 == integers2 integers1 and integers2 are equal integers1[5] is 13

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

8.9 Converting between Types 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

8.9 Converting between Types 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;

8.9 Converting between Types 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

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) 1 // Fig. 8.7: string1.h 2 // String class definition. 3 #ifndef STRING1_H 4 #define STRING1_H 5 6 #include <iostream> 7 8 using std::ostream; 9 using std::istream; 10 11 class String { 12 friend ostream & operator <<( ostream &, const String & ); 13 friend istream & operator >>( istream &, String & ); 14 15 public : 16 String( const char * = "" ); // conversion/default ctor 17 String( const String & ); // copy constructor 18 ~String(); // destructor 19 20 const String & operator =( const String & ); // assignment 21 const String & operator +=( const String & ); // concatenation 22 23 bool operator !() const ; // is String empty? 24 bool operator ==( const String & ) const ; // test s1 == s2 25 bool operator <( const String & ) const ; // test s1 < s2 26 Conversion constructor to make a String from a char * . 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.

string1.h (2 of 3) 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 36 { 37 return right < * this ; 38 39 } // end function operator> 40 41 // test s1 <= s2 42 bool operator <=( const String &right ) const 43 { 44 return !( right < * this ); 45 46 } // end function operator <= 47 48 // test s1 >= s2 49 bool operator >=( const String &right ) const 50 { 51 return !( * this < right ); 52 53 } // end function operator>=

string1.h (3 of 3) 54 55 char & operator []( int ); // subscript operator 56 const char & operator []( int ) 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 64 char *sPtr; // pointer to start of string 65 66 void setString( const char * ); // utility function 67 68 }; // end class String 69 70 #endif Overload the function call operator () to return a substring. This operator can have any amount of operands. Two overloaded subscript operators, for const and non- const objects.

string1.cpp (1 of 8) 1 // Fig. 8.8: string1.cpp 2 // Member function definitions for class String. 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 8 #include <iomanip> 9 10 using std::setw; 11 12 #include <new> // C++ standard "new" operator 13 14 #include <cstring> // strcpy and strcat prototypes 15 #include <cstdlib> // exit prototype 16 17 #include "string1.h" // String class definition 18 19 // conversion constructor converts char * to String 20 String::String( const char *s ) 21 : length( strlen( s ) ) 22 { 23 cout << "Conversion constructor: " << s << '\n' ; 24 setString( s ); // call utility function 25 26 } // end String conversion constructor

string1.cpp (2 of 8) 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 37 // destructor 38 String::~String() 39 { 40 cout << "Destructor: " << sPtr << '\n' ; 41 delete [] sPtr; // reclaim string 42 43 } // end ~String destructor 44 45 // overloaded = operator; avoids self assignment 46 const String &String:: operator =( const String &right ) 47 { 48 cout << "operator= called\n" ; 49 50 if ( &right != this ) { // avoid self assignment 51 delete [] sPtr; // prevents memory leak 52 length = right.length; // new String length 53 setString( right.sPtr ); // call utility function 54 }

string1.cpp (3 of 8) 55 56 else 57 cout << "Attempted assignment of a String to itself\n" ; 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. 65 const String &String:: operator +=( const String &right ) 66 { 67 size_t newLength = length + right.length; // new length 68 char *tempPtr = new char [ newLength + 1 ]; // create memory 69 70 strcpy( tempPtr, sPtr ); // copy sPtr 71 strcpy( tempPtr + length, right.sPtr ); // copy right.sPtr 72 73 delete [] sPtr; // reclaim old space 74 sPtr = tempPtr; // assign new array to sPtr 75 length = newLength; // assign new length to length 76 77 return * this ; // enables cascaded calls 78 79 } // end function operator+= 80

string1.cpp (4 of 8) 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 ) == 0 ; 92 93 } // end function operator== 94 95 // is this String less than right String? 96 bool String:: operator <( const String &right ) const 97 { 98 return strcmp( sPtr, right.sPtr ) < 0 ; 99 100 } // end function operator< 101

string1.cpp (5 of 8) 102 // return reference to character in String as lvalue 103 char &String:: operator []( int subscript ) 104 { 105 // test for subscript out of range 106 if ( subscript < 0 || subscript >= length ) { 107 cout << "Error: Subscript " << subscript 108 << " out of range" << endl; 109 110 exit( 1 ); // terminate program 111 } 112 113 return sPtr[ subscript ]; // creates lvalue 114 115 } // end function operator[] 116 117 // return reference to character in String as rvalue 118 const char &String:: operator []( int subscript ) const 119 { 120 // test for subscript out of range 121 if ( subscript < 0 || subscript >= length ) { 122 cout << "Error: Subscript " << subscript 123 << " out of range" << endl; 124 125 exit( 1 ); // terminate program 126 } 127 128 return sPtr[ subscript ]; // creates rvalue 129 130 } // end function operator[]

string1.cpp (6 of 8) 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 140 141 // determine length of substring 142 int len; 143 144 if ( ( subLength == 0 ) || ( index + subLength > length ) ) 145 len = length - index; 146 else 147 len = subLength; 148 149 // allocate temporary array for substring and 150 // terminating null character 151 char *tempPtr = new char [ len + 1 ]; 152 153 // copy substring into char array and terminate string 154 strncpy( tempPtr, &sPtr[ index ], len ); 155 tempPtr[ len ] = '\0' ;

string1.cpp (7 of 8) 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 166 int String::getLength() const 167 { 168 return length; 169 170 } // end function getLenth 171 172 // utility function called by constructors and operator= 173 void String::setString( const char *string2 ) 174 { 175 sPtr = new char [ length + 1 ]; // allocate memory 176 strcpy( sPtr, string2 ); // copy literal to object 177 178 } // end function setString

string1.cpp (8 of 8) 179 180 // overloaded output operator 181 ostream & operator <<( ostream &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 190 istream & operator >>( istream &input, String &s ) 191 { 192 char temp[ 100 ]; // buffer to store input 193 194 input >> setw( 100 ) >> temp; 195 s = temp; // use String class assignment operator 196 197 return input; // enables cascading 198 199 } // end function operator>>

fig08_09.cpp (1 of 4) 1 // Fig. 8.9: fig08_09.cpp 2 // String class test program. 3 #include <iostream> 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" ); 14 String s3; 15 16 // test overloaded equality and relational operators 17 cout << "s1 is \"" << s1 << "\"; s2 is \"" << s2 18 << "\"; s3 is \"" << s3 << '\"' 19 << "\n\nThe results of comparing s2 and s1:" 20 << "\ns2 == s1 yields " 21 << ( s2 == s1 ? "true" : "false" ) 22 << "\ns2 != s1 yields " 23 << ( s2 != s1 ? "true" : "false" ) 24 << "\ns2 > s1 yields " 25 << ( s2 > s1 ? "true" : "false" )

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 << "\n\nTesting !s3:\n" ; 35 36 if ( !s3 ) { 37 cout << "s3 is empty; assigning s1 to s3;\n" ; 38 s3 = s1; // test overloaded assignment 39 cout << "s3 is \"" << s3 << "\"" ; 40 } 41 42 // test overloaded String concatenation operator 43 cout << "\n\ns1 += s2 yields s1 = " ; 44 s1 += s2; // test overloaded concatenation 45 cout << s1; 46 47 // test conversion constructor 48 cout << "\n\ns1 += \" to you\" yields\n" ; 49 s1 += " to you" ; // test conversion constructor 50 cout << "s1 = " << s1 << "\n\n" ;

fig08_09.cpp (3 of 4) 51 52 // test overloaded function call operator () for substring 53 cout << "The substring of s1 starting at\n" 54 << "location 0 for 14 characters, s1(0, 14), is:\n" 55 << s1( 0 , 14 ) << "\n\n" ; 56 57 // test substring "to-end-of-String" option 58 cout << "The substring of s1 starting at\n" 59 << "location 15, s1(15, 0), is: " 60 << s1( 15 , 0 ) << "\n\n" ; // 0 is "to end of string" 61 62 // test copy constructor 63 String *s4Ptr = new String( s1 ); 64 cout << "\n*s4Ptr = " << *s4Ptr << "\n\n" ; 65 66 // test assignment (=) operator with self-assignment 67 cout << "assigning *s4Ptr to *s4Ptr\n" ; 68 *s4Ptr = *s4Ptr; // test overloaded assignment 69 cout << "*s4Ptr = " << *s4Ptr << '\n' ; 70 71 // test destructor 72 delete s4Ptr; 73

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 << "\n\n" ; 79 80 // test subscript out of range 81 cout << "Attempt to assign 'd' to s1[30] yields:" << endl; 82 s1[ 30 ] = 'd'; // ERROR: subscript out of range 83 84 return 0; 85 86 } // end main

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 Testing !s3: s3 is empty; assigning s1 to s3; operator= called s3 is "happy" s1 += s2 yields s1 = happy birthday s1 += " to you" yields Conversion constructor: to you Destructor: to you s1 = happy birthday to you The constructor and destructor are called for the temporary String (converted from the char * “to you” ).

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 The substring of s1 starting at location 15, s1(15, 0), is: to you Destructor: to you Copy constructor: happy birthday to you *s4Ptr = happy birthday to you assigning *s4Ptr to *s4Ptr operator= called Attempted assignment of a String to itself *s4Ptr = happy birthday to you Destructor: happy birthday to you

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

8.11 Overloading ++ and -- 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 )

8.11 Overloading ++ and -- 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

8.11 Overloading ++ and -- 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

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

date1.h (1 of 2) 1 // Fig. 8.10: date1.h 2 // Date class definition. 3 #ifndef DATE1_H 4 #define DATE1_H 5 #include <iostream> 6 7 using std::ostream; 8 9 class Date { 10 friend ostream & operator <<( ostream &, const Date & ); 11 12 public : 13 Date( int m = 1 , int d = 1 , int y = 1900 ); // constructor 14 void setDate( int , int , int ); // set the date 15 16 Date & operator ++(); // preincrement operator 17 Date operator ++( int ); // postincrement operator 18 19 const Date & operator +=( int ); // add days, modify object 20 21 bool leapYear( int ) const ; // is this a leap year? 22 bool endOfMonth( int ) const ; // is this end of month? Note difference between pre and post increment.

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 34 #endif

date1.cpp (1 of 5) 1 // Fig. 8.11: date1.cpp 2 // Date class member function definitions. 3 #include <iostream> 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 11 // Date constructor 12 Date::Date( int m, int d, int y ) 13 { 14 setDate( m, d, y ); 15 16 } // end Date constructor 17 18 // set month, day and year 19 void Date::setDate( int mm, int dd, int yy ) 20 { 21 month = ( mm >= 1 && mm <= 12 ) ? mm : 1 ; 22 year = ( yy >= 1900 && yy <= 2100 ) ? yy : 1900 ; 23

date1.cpp (2 of 5) 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 <= days[ month ] ) ? dd : 1 ; 29 30 } // end function setDate 31 32 // overloaded preincrement operator 33 Date &Date:: operator ++() 34 { 35 helpIncrement(); 36 37 return * this ; // reference return to create an lvalue 38 39 } // end function operator++ 40 41 // overloaded postincrement operator; note that the dummy 42 // integer parameter does not have a parameter name 43 Date Date:: operator ++( int ) 44 { 45 Date temp = * this ; // hold current state of object 46 helpIncrement(); 47 48 // return unincremented, saved, temporary object 49 return temp; // value return; not a reference return 50 51 } // end function operator++ 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.

date1.cpp (3 of 5) 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 61 } // end function operator+= 62 63 // if the year is a leap year, return true; 64 // otherwise, return false 65 bool Date::leapYear( int testYear ) const 66 { 67 if ( testYear % 400 == 0 || 68 ( testYear % 100 != 0 && testYear % 4 == 0 ) ) 69 return true ; // a leap year 70 else 71 return false ; // not a leap year 72 73 } // end function leapYear 74

date1.cpp (4 of 5) 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 84 85 // function to help increment the date 86 void Date::helpIncrement() 87 { 88 // day is not end of month 89 if ( !endOfMonth( day ) ) 90 ++day; 91 92 else 93 94 // day is end of month and month < 12 95 if ( month < 12 ) { 96 ++month; 97 day = 1 ; 98 } 99

date1.cpp (5 of 5) 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 110 ostream & operator <<( ostream &output, const Date &d ) 111 { 112 static char *monthName[ 13 ] = { "" , "January" , 113 "February" , "March" , "April" , "May" , "June" , 114 "July" , "August" , "September" , "October" , 115 "November" , "December" }; 116 117 output << monthName[ d.month ] << ' ' 118 << d.day << ", " << d.year; 119 120 return output; // enables cascading 121 122 } // end function operator<<

fig08_12.cpp (1 of 2) 1 // Fig. 8.12: fig08_12.cpp 2 // Date class test program. 3 #include <iostream> 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 1, 1900 13 Date d2( 12 , 27 , 1992 ); 14 Date d3( 0 , 99 , 8045 ); // invalid date 15 16 cout << "d1 is " << d1 << "\nd2 is " << d2 17 << "\nd3 is " << d3; 18 19 cout << "\n\nd2 += 7 is " << ( d2 += 7 ); 20 21 d3.setDate( 2 , 28 , 1992 ); 22 cout << "\n\n d3 is " << d3; 23 cout << "\n++d3 is " << ++d3; 24 25 Date d4( 7 , 13 , 2002 );

fig08_12.cpp (2 of 2) 26 27 cout << "\n\nTesting the preincrement operator:\n" 28 << " d4 is " << d4 << '\n'; 29 cout << "++d4 is " << ++d4 << '\n' ; 30 cout << " d4 is " << d4; 31 32 cout << "\n\nTesting the postincrement operator:\n" 33 << " d4 is " << d4 << '\n' ; 34 cout << "d4++ is " << d4++ << '\n' ; 35 cout << " d4 is " << d4 << endl; 36 37 return 0 ; 38 39 } // end main

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 Testing the postincrement operator: d4 is July 14, 2002 d4++ is July 14, 2002 d4 is July 15, 2002

8.13 Standard 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

8.13 Standard Library Classes string and vector Class string Header <string>, namespace std Can initialize string s1(“hi”); Overloaded << cout << s1 Overloaded relational operators == != >= > <= < Assignment operator = Concatenation (overloaded += )

8.13 Standard Library Classes 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)

fig08_13.cpp (1 of 4) 1 // Fig. 8.13: fig08_13.cpp 2 // Standard library string class test program. 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 8 #include <string> 9 10 using std::string; 11 12 int main() 13 { 14 string s1( "happy" ); 15 string s2( " birthday" ); 16 string s3; 17 18 // test overloaded equality and relational operators 19 cout << "s1 is \"" << s1 << "\"; s2 is \"" << s2 20 << "\"; s3 is \"" << s3 << '\"' 21 << "\n\nThe results of comparing s2 and s1:" 22 << "\ns2 == s1 yields " 23 << ( s2 == s1 ? "true" : "false" ) 24 << "\ns2 != s1 yields " 25 << ( s2 != s1 ? "true" : "false" )

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 empty 36 cout << "\n\nTesting s3.empty():\n" ; 37 38 if ( s3.empty() ) { 39 cout << "s3 is empty; assigning s1 to s3;\n" ; 40 s3 = s1; // assign s1 to s3 41 cout << "s3 is \"" << s3 << "\"" ; 42 } 43 44 // test overloaded string concatenation operator 45 cout << "\n\ns1 += s2 yields s1 = " ; 46 s1 += s2; // test overloaded concatenation 47 cout << s1; 48

fig08_13.cpp (3 of 4) 49 // test overloaded string concatenation operator 50 // with C-style string 51 cout << "\n\ns1 += \" to you\" yields\n" ; 52 s1 += " to you" ; 53 cout << "s1 = " << s1 << "\n\n" ; 54 55 // test string member function substr 56 cout << "The substring of s1 starting at location 0 for\n" 57 << "14 characters, s1.substr(0, 14), is:\n" 58 << s1.substr( 0 , 14 ) << "\n\n" ; 59 60 // test substr "to-end-of-string" option 61 cout << "The substring of s1 starting at\n" 62 << "location 15, s1.substr(15), is:\n" 63 << s1.substr( 15 ) << '\n' ; 64 65 // test copy constructor 66 string *s4Ptr = new string( s1 ); 67 cout << "\n*s4Ptr = " << *s4Ptr << "\n\n" ; 68 69 // test assignment (=) operator with self-assignment 70 cout << "assigning *s4Ptr to *s4Ptr\n" ; 71 *s4Ptr = *s4Ptr; 72 cout << "*s4Ptr = " << *s4Ptr << '\n' ; 73

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 << "\n\n" ; 82 83 // test subscript out of range with string member function "at" 84 cout << "Attempt to assign 'd' to s1.at( 30 ) yields:" << endl; 85 s1.at( 30 ) = 'd'; // ERROR: subscript out of range 86 87 return 0 ; 88 89 } // end main

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; s3 is "happy" s1 += s2 yields s1 = happy birthday s1 += " to you" yields s1 = happy birthday to you The substring of s1 starting at location 0 for 14 characters, s1.substr(0, 14), is: happy birthday

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 ) yields: abnormal program termination

8.13 Standard Library Classes 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

fig08_14.cpp (1 of 5) 1 // Fig. 8.14: fig08_14.cpp 2 // Demonstrating standard library class vector. 3 #include <iostream> 4 5 using std::cout; 6 using std::cin; 7 using std::endl; 8 9 #include <iomanip> 10 11 using std::setw; 12 13 #include <vector> 14 15 using std::vector; 16 17 void outputVector( const vector< int > & ); 18 void inputVector( vector< int > & ); 19 20 int main() 21 { 22 vector< int > integers1( 7 ); // 7-element vector< int > 23 vector< int > integers2( 10 ); // 10-element vector< int > 24

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() 34 << "\nvector after initialization:\n" ; 35 outputVector( integers2 ); 36 37 // input and print integers1 and integers2 38 cout << "\nInput 17 integers:\n" ; 39 inputVector( integers1 ); 40 inputVector( integers2 ); 41 42 cout << "\nAfter input, the vectors contain:\n" 43 << "integers1:\n" ; 44 outputVector( integers1 ); 45 cout << "integers2:\n" ; 46 outputVector( integers2 ); 47 48 // use overloaded inequality (!=) operator 49 cout << "\nEvaluating: integers1 != integers2\n" ; 50

fig08_14.cpp (3 of 5) 51 if ( integers1 != integers2 ) 52 cout << "integers1 and integers2 are not equal\n" ; 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 " 59 << integers3.size() 60 << "\nvector after initialization:\n" ; 61 outputVector( integers3 ); 62 63 64 // use overloaded assignment (=) operator 65 cout << "\nAssigning integers2 to integers1:\n" ; 66 integers1 = integers2; 67 68 cout << "integers1:\n" ; 69 outputVector( integers1 ); 70 cout << "integers2:\n" ; 71 outputVector( integers1 ); 72

fig08_14.cpp (4 of 5) 73 // use overloaded equality (==) operator 74 cout << "\nEvaluating: integers1 == integers2\n" ; 75 76 if ( integers1 == integers2 ) 77 cout << "integers1 and integers2 are equal\n" ; 78 79 // use overloaded subscript operator to create rvalue 80 cout << "\nintegers1[5] is " << integers1[ 5 ]; 81 82 // use overloaded subscript operator to create lvalue 83 cout << "\n\nAssigning 1000 to integers1[5]\n" ; 84 integers1[ 5 ] = 1000 ; 85 cout << "integers1:\n" ; 86 outputVector( integers1 ); 87 88 // attempt to use out of range subscript 89 cout << "\nAttempt to assign 1000 to integers1.at( 15 )" 90 << endl; 91 integers1.at( 15 ) = 1000; // ERROR: out of range 92 93 return 0 ; 94 95 } // end main 96

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 107 108 if ( i % 4 != 0 ) 109 cout << endl; 110 111 } // end function outputVector 112 113 // input vector contents 114 void inputVector( vector< int > &array ) 115 { 116 for ( int i = 0 ; i < array.size(); i++ ) 117 cin >> array[ i ]; 118 119 } // end function inputVector

fig08_14.cpp output (1 of 2) Size of vector integers1 is 7 vector after initialization: 0 0 0 0 0 0 0 Size of vector integers2 is 10 vector after initialization: 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 16 17 After input, the vectors contain: integers1: 1 2 3 4 5 6 7 integers2: 8 9 10 11 12 13 14 15 16 17 Evaluating: integers1 != integers2 integers1 and integers2 are not equal

fig08_14.cpp output (2 of 2) Size of vector integers3 is 7 vector after initialization: 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 16 17 Evaluating: integers1 == integers2 integers1 and integers2 are equal integers1[5] is 13 Assigning 1000 to integers1[5] integers1: 8 9 10 11 12 1000 14 15 16 17 Attempt to assign 1000 to integers1.at( 15 ) abnormal program termination

Operator overloading

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Operator overloading