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Object Orientedj
Programming using C++
Lecture – 7
Classes and Dynamic Memory
Classes and DMA
Classes with static data:
Constructor is used to initialize the data to the desiredConstructor is used to initialize the data to the desired
values, instead of garbage
Destructor has no real use
Classes can contain dynamic data:
Constructor can be used to automatically allocate space
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Destructor’s role is critical, such that it is required to de-
allocate the memory acquired at object’s instantiation
If Not??
Memory Leak!!
Classes and DMA (contd..)
#include using namespace std;g p ; class Singer { private: char* singer_name; char* album_name; public:
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Singer(char* s_name, char* a_name); ~Singer(); void display(); };
Classes and DMA (contd..)
Singer::Singer(char* s_name, char* a_name) {{ singer_name = new char[strlen(s_name) + 1]; strcpy(singer_name, s_name);
album_name = new char[strlen(a_name) + 1]; strcpy(album_name, a_name); }
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Singer::~Singer() { delete[] singer_name; delete[] album_name; }
Friend Functions and Classes
Data Accessibility
Default visibility of data in a class is private Additionally, data and functions can bedd ll d d f b made private when required
Means it is not accessible out side the class
Only member functions can access it
Objects can provide an indirect access by passing
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object arguments to each others’ member
functions
No external function can access the private data
Data Accessibility - Exceptions
C++ provides a flexibility to access the private data of a class by an external function, making it as a friendclass by an external function, making it as a friend function.
Similarly, a class can provide an access to its private data to another class, by making it as a friend class.
f d f l d f d d h
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A friend function or a class is defined outside the scope of a class which has made them friends.
Example
my_Class and student are two different classes HoweverHowever, my_Class is made a friend of student in order my Class is made a friend of student in order to access all its private data A function display_students_from_main() is defined to display all the private data of my_Class, and hence is made friend of it An external function set_students_from_main() can easily access all the public data/functions of my Class
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easily access all the public data/functions of my_Class, just by using its reference See example hand out
THIS Pointer
How does C++ ensure that the proper object is referenced?is referenced?
C++ compiler maintains a pointer, called the this
pointer.
When a member function is called, this pointer
contains the address of the object, for which the
function is invoked
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function is invoked.
Therefore, member functions of an object can
access the local data using this pointer
THIS Pointer (contd..)
Function Definition
void Singer::display(id Si di l ( SiSi nger* this* thi ))
// Singer* this is hidden to the programmer
//automatically added by compiler
Function Call singer1.display( &singer1 ) ;
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//&singer1 is hidden to the programmer
//automatically added by compiler
THIS Pointer (contd..)
Function Definition void Singer::display()void Singer::display() { //Normal Access cout<<"Singer name is : "<<singer_name<<endl; cout<<"Album name is : "<<album_name<<endl;
//Access using this pointer
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//Access using this pointer cout<<"Singer name is : "<<this->singer_name<<endl; cout<<"Album name is : "<<this->album_name<<endl;
//BOTH CASES WILL WORK }
