C++ Separate Overload

In C++, each operator overload is treated as a separate function based on its parameter types and order. If the order of operands changes, the compiler expects a different function. Even when performing the same operation, C++ does not automatically reverse or convert the arguments.

This is common when working with binary operators (like +) between a class and a built-in type. For example, to support both SomeClass + someValue and someValue + SomeClass, two separate overloads must be written.

Syntax

Here’s a syntax of showing how to write two separate overloads for a binary operator when the order of operands can vary:

// Overload for: object + value
ClassName operator+(const ClassName& obj, SomeType value);

// Overload for: value + object
ClassName operator+(SomeType value, const ClassName& obj);

• The first overload allows expressions like object + value.
• The second overload supports the reverse order: value + object.
• These are treated as distinct functions in C++, so both must be defined separately if both usage orders are needed.
• SomeType can be any type like int, float, or even another class.

Example: Using the + operator in both operand orders

The following example demonstrates how to overload a binary operator in both operand orders for a class named Score. This supports operations like Score + int and int + Score:

#include <iostream>
using namespace std;

class Score {
  private:
    int points;

  public:
    Score(int p) : points(p) {}

    void display() const {
      cout << "Points: " << points << endl;
    }

    // Friend function for Score + int
    friend Score operator+(const Score& s, int extra);

    // Friend function for int + Score
    friend Score operator+(int extra, const Score& s);
};

// Definition for Score + int
Score operator+(const Score& s, int extra) {
  return Score(s.points + extra);
}

// Definition for int + Score
Score operator+(int extra, const Score& s) {
  return Score(extra + s.points);
}

int main() {
  Score s1(50);

  Score result1 = s1 + 20;
  Score result2 = 30 + s1;

  result1.display();
  result2.display();

  return 0;
}

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The above example will result in the following output:

Points: 70
Points: 80

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In this example:

• The Score class stores a private points value.
• Two separate overloads of the + operator are defined to handle different operand orders.
• Each overload is declared as a friend to allow direct access to private data.
• This approach ensures that both Score + value and value + Score expressions compile correctly, as C++ does not automatically reverse the operands.

Codebyte Example

The following codebyte example overloads the plus (+) operator using friend functions to support both Distance + value and value + Distance. It demonstrates how separate overloads are defined to handle different operand orders. Compile the code to see the output of both operations.

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