3. Objects #

Created Wednesday 08 January 2020

Syntax #

class_name object_name; // this allocates memory. variable of type student in the stack.
class_name * object_name = new class_name; 	// this creates a pointer in stack to a memory location in heap.

• This is **exactly **like we do for in-built data types.
• Memory allocated for an object = sum of the memory of the attributes. No meta data is stored in the objects, viz functions, static variables.

Q) Can we create an object anywhere we like? A) We can create anywhere after the class has been defined.

• To include classes from other files, use this syntax.

#include "absolute_path/class_file_name.extnsn" // different directory
#include "file.extnsn" // file in the current directory

• #include just copies text from the *class_file_name.extnsn *to the current file.

Accessing members of an object #

• Variable

obj.name; // access 'name' attribute of 'obj' object
obj.fact() // call fact() function of 'obj'
// . is called the selector operator

• Pointer

(*p).name;
(*p).fact();

// C++  has a better way, a simple expression. Does exactly the same thing.
p->name;
p->fact();

Concept of Access Specifier in C++ #

• Access Specifiers are keywords associated with members(attributes, functions) which modify the level of access.
• They are applicable only outside the class, i.e they have no meaning inside the class.
• There are three: public, private and protected.

Syntax:

class A{
	public:
		int a;
		int b;
	private:
		void f();
};

• We can have multiple sections of the same specifier too.

class A{
	public:
		int a;
		int b;
	private:
		void f();
	public: //allowed
		int c;
};

Notes:

• When not specified, all things are private by default in a class.

class Car {
  int a; // a is private
};

• The access modifiers work on class level, and not on object level i.e, two objects of the same class can access each others private data.