Overloading

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KyraThompson
Published Feb 27, 2023
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Overloading allows for more than one definition of a function or operator in the same scope. Respectively, it is called function overloading and operator overloading.

Function Overloading

Function overloading begins with declaring a function with the same name as a previously declared function but with different parameters.

Note: Each declaration must have different parameters. Only changing the function’s return type will not work.

Syntax

Since a function can be overloaded multiple times, the syntax can look different case-to-case. The following is an outline of what an overloaded function could look like:

functionName(parameters1);
functionName(parameters2);

More declarations can be added as needed and a declaration has the following parts:

  • functionName: The name of the function that is the same for each definition.
  • parameters1 and parameters2: Parameters for each definition, these must be different for each definition.

Example

The following example overloads the multiply() function:

#include <iostream>
using namespace std;


void multiply(int x, int y) {
  cout << "The product of " << x << " and " << y << " is: " << (x*y) << endl;
}


void multiply(double x, double y) {
  cout << "The product of " << x << " and " << y << " is: " << (x*y) << endl;
}


int main() {
  multiply(20,10);
  multiply(80.2, 90.99);
}

This will output:

The product of 20 and 10 is: 200
The product of 80.2 and 90.99 is: 7297.4

Operator Overloading

Operator overloading redefines built-in operators for user-defined classes. When an overloaded operator is called, the compiler determines which definition to use based on the arguments provided. The following operators can be overloaded:

Category Operators Names
Arithmetic +, -, *, /, %, ++, —- add/positive, subtract/negative, multiply, divide, modulo, increment, decrement
Assignment =, +=,*=, /=,-=, %=, &=, ^=, &#124;=, <<=, >>= assign, add & assign, multiply & assign, divide & assign, subtract & assign, modulo & assign, bitwise AND & assign, bitwise exclusive OR & assign, bitwise inclusive OR & assign, shift bits left & assign, shift bits right & assign
Bitwise &, &#124;, ^, ~, <<, >> bitwise AND, bitwise inclusive OR, bitwise exclusive OR, bit inversion, shift bits left, shift bits right
Logical &&, &#124;&#124;, ! logical AND, logical OR, logical NOT
Relational ==, !=, >, <, >=, <= equal to, not equal to, greater than, less than, greater than or equal to, less than or equal to
Member Access ->, ->* member of pointer, pointer to member of pointer
Allocation/Deallocation new, new[], delete, delete[] new, new & allocate, delete, delete & allocate
Other ,, (), [] comma, function call, subscript/array index

The operators below cannot be overloaded:

Category Operators Names
Conditional (or Ternary) ? conditional
Scope :: scope access
Member Access ., .* member of object, pointer to member of object

Syntax

class className {
  public:
    returnType operator symbol (arguments) {
      // code goes here
    }
};

The operator keyword is used along with the following:

  • className: Name of the class.
  • returnType: Return type of the function.
  • symbol: Operator in which to overload.
  • arguments: Arguments to pass in.

Codebyte Example

The following codebyte example overloads the plus (+) operator within the Pyramid class and returns the volume of two pyramids added together:

Code
Output
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