Operator Overloading  «Prev  Next»
Lesson 2 Why overload operators?
Objective Understand why operator overloading is useful in C++.

Operator Overloading in C++: Utility and Significance

Abstract Operator overloading, a hallmark feature of C++, grants the ability to redefine or extend the semantics of operators for user-defined data types. By providing an intuitive and consistent interface for object interaction, operator overloading encapsulates the essence of abstraction in object-oriented programming.
  1. Introduction:
    In the realm of computer programming, the ability for languages to convey intent, not just instruction, is a testament to their evolution. C++, as an object-oriented and generic programming language, introduces several advanced features to help bridge the conceptual gap between problem domains and their representations. Among these, operator overloading stands as a significant concept that enhances the expressiveness of the language.
  2. The Principle of Operator Overloading:
    Operator overloading allows user-defined types to exhibit behavior analogous to built-in types by redefining or extending standard operators. In essence, when we define how specific operators work for our custom objects, we're "overloading" their traditional operational semantics.
  3. The Utility of Operator Overloading in C++
    Understanding the true utility of operator overloading necessitates a deeper look into its practical applications:
    1. 3.1. Intuitive Interaction: Operator overloading permits custom data types to interact using traditional operators. For instance, mathematical objects such as `Complex` numbers or `Vector` can be added using the '+' operator, yielding a syntax that closely mirrors mathematical conventions.
    2. 3.2. Consistent Syntax: It encourages a uniform interface. Instead of having disparate function names like `addMatrices()` or `concatenateStrings()`, developers can use the familiar '+' operator for both, promoting syntactic consistency.
    3. 3.3. Enhanced Abstraction: With operator overloading, one can encapsulate intricate operations behind well-understood symbols, shielding users from underlying complexities. For instance, the '<<' operator, when overloaded, allows custom objects to be streamed directly into output streams seamlessly.
    4. 3.4. Extending Language Semantics: Beyond redefining existing operators, C++ permits the creation of novel operational semantics for user-defined types. This capability empowers developers to mold the language to better fit particular domain-specific needs.
  4. Conclusion:
    Operator overloading in C++ is not merely a syntactic luxury; it's a potent tool that underpins the core tenets of object-oriented design: abstraction, encapsulation, and polymorphism. By allowing objects to interact in a manner that's intuitive, consistent, and expressive, operator overloading reinforces C++'s stance as a language that strives to merge human intent with computational rigor. As budding computer scientists, understanding and adeptly employing this concept will enable students to craft software that's not only functionally robust but also conceptually coherent.

Reason behind Operator Overloading in C++

Just as a function name, such as print(), can be given a variety of meanings that depend on its arguments, so can an operator be given additional meanings. For example, the expression a + b has different meanings depending on the types of the variables a and b. Overloading the + operator for user-defined types allows them to be used in addition expressions, in much the same way as a native type.
The expression a + b could mean string concatenation, complex number addition, or integer addition, depending on whether the variables were the ADT string, the ADT complex, or the native type int.
Although meanings can be added to operators, their associativity and precedence remain the same. For example, the multiplication operator will remain of higher precedence than the addition operator.

Some of the most commonly used operators in C++ are the arithmetic operators.
  1. the plus operator (+),
  2. minus operator (-),
  3. multiplication operator (*), and
  4. division operator (/).
All of the arithmetic operators are binary operators and all four of these operators are overloaded in the exact same way.

Operator overloading allows operators to be redefined and used where one or both of the operands are of a user-defined class. When done correctly, this can simplify the code and make user-defined types as easy to use as the primitive types.

Operator overloading example

In the example below there is a class called MyNum with an integer field and a constructor for setting that field. The class also has an addition method that adds two MyNum objects together and returns the result as a new object.

class MyNum{
  int val;
 MyNum(int i) : val(i) {}
 MyNum add(MyNum &a){ 
  return MyNum( val + a.val ); 

Two MyNum instances can be added together using this method.
MyNum a = MyNum(10), b = MyNum(5);
MyNum c = a.add(b);