Operator Overloading in C++


Operator Overloading
What is an operator?
Operators are symbolic representation of mathematical or logical operations that can be performed on one or more operands. In C++, there are following operators present:
Operator
Type
Number of operands
++,--
Unary Operator
1
+,-,*,/,%
Arithmetic operator
2
<,<=,>,>=,==,!=
Relational operator
2
&&,||,!
Logical operator
2
&,|,<<,>>,~,^
Bitwise operator
2
=,+=,-=,*=,/=,%=
Assignment operator
2
?:
Ternary operator
3

There are some special operators such as . (dot operator), :: (Scope resolution) and sizeof operator. Each of them has a special purpose such as the dot operator is used for Member resolution, :: is used to change the resolution of a assignment or Member and sizeof is a C++ compiler unary operator which is used to determine the memory size of its operand.
Operator precedence table is as follows-
OPERATOR
DESCRIPTION
ASSOCIATIVITY
()
Parentheses (function call)
left-to-right
[]
Brackets (array subscript)

.
Member selection via object name

->
Member selection via pointer

++/–
Postfix increment/decrement

++/–
Prefix increment/decrement
right-to-left
+/-
Unary plus/minus

!~
Logical negation/bitwise complement

(type)
Cast (convert value to temporary value of type)

*
Dereference

&
Address (of operand)

sizeof
Determine size in bytes on this implementation

*,/,%
Multiplication/division/modulus
left-to-right
+/-
Addition/subtraction
left-to-right
<< , >>
Bitwise shift left, Bitwise shift right
left-to-right
< , <=
Relational less than/less than or equal to
left-to-right
> , >=
Relational greater than/greater than or equal to
left-to-right
== , !=
Relational is equal to/is not equal to
left-to-right
&
Bitwise AND
left-to-right
^
Bitwise exclusive OR
left-to-right
|
Bitwise inclusive OR
left-to-right
&&
Logical AND
left-to-right
||
Logical OR
left-to-right
?:
Ternary conditional
right-to-left
=
Assignment
right-to-left
+= , -=
Addition/subtraction assignment

*= , /=
Multiplication/division assignment

%= , &=
Modulus/bitwise AND assignment

^= , |=
Bitwise exclusive/inclusive OR assignment

<>=
Bitwise shift left/right assignment

,
expression separator
left-to-right

Operator Overloading
In C++, the operators work on in-built data types without any issues but if we want to use operators for user-defined classes then we must Operator Overloading.
In overloading, a declaration which is similar (in name/operator) is declared in the same scope, and the compiler decided which definition is appropriate depending on the argument types passed with the call of the declaration. This process is known as overload resolution. Overloading can be done for functions as well as operators. For operator overloading the keyword operator and operator symbol are required as the function name. User cannot define their own operators.
In operator overloading, all above mentioned operators can be overloaded with the exceptions-
1)      .           (dot operator)
2)      ::          (Scope resolution operator)
3)      ?:         (Ternary operator)
4)      sizeof   operator.
In operator overloading, At least one operand must be a user defined class object. Also, Assignment operator creates a default operator with every class, such that it can assign right side to left side. Conversion operators can be used to convert data from one type to another.
The operator declaration is called in base class of the first operand. The second operator can be passed by reference or by value during the operator call.
Example:

Limitations on Operator overloading-
1)      The precedence and associativity of the operators cannot be changed.
2)      Number of operands for an operator cannot be changed.
3)      One operand must be of used defined class.
4)      User cannot define new operators.

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