Page 105 - DCAP404 _Object Oriented Programming

Object-oriented Programming

Notes printx ();
}
}
2. A static object is really just an encapsulation of data and related functions.
3. A static object does not have to have a main function, but to be useful it typically has at
least one public function that can be called from somewhere else.

Task By default, an object or variable that is defined outside all blocks has static duration
and external linkage. Justify.

Self Assessment

Fill in the blanks:
6. Static duration means that the object or variable is allocated when the program starts and
is …………………………. when the program ends.
7. You cannot declare the members of a ………………… as static.
8. The threads invoking methods on static objects must wait until the object is fully
……………………. .
9. A class is a collection of ……………………….., which are variables of various types,
including other classes.
10. A member function definition begins with the name of the class, followed by two colons,
the name of the………………………………, and its parameters.

5.4 Friend Functions

Object oriented programming paradigm secures data because of the data hiding and data
encapsulation features. Data members declared as private in a class are restricted from access by
non-member functions. The private data values can be neither read nor written by non-member
functions. Any attempt made directly to access these members, will result in an error message as
“inaccessible data-type” during compilation.
The best way to access a private data member by a non-member function is to change a private
data member to a public group. But this goes against the concept of data hiding and data
encapsulation. A special mechanism available known as friend function allows non-member
functions to access private data. A friend function may be either declared or defined within the
scope of a class definition. The keyword friend informs the compiler that it is not a member
function nor the property of the class.

The general syntax of the friend function is:
friend <return_type> <function_name>(argument list);
friend is a keyword. A friend declaration is valid only within or outside the class definition. The
following code snippet shows how a friend function is defined.
class sample
{

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