Pass by Reference

Overview

Pass by value copies the argument. Pass by reference passes the actual memory address, allowing the function to modify the original variable and avoiding expensive copying.

Syntax

cpp

// Pass by Value (Copies)
void modifyValue(int x) { x = 99; }

// Pass by Reference (Modifies original)
void modifyRef(int& x) { x = 99; }

// Pass by Const Reference (Read-only, no copy overhead)
void printBigObject(const std::string& str) { cout << str; }

Common Pitfalls

Forgetting the ampersand `&` and accidentally passing a massive vector by value, causing huge slowdowns.

Interview Tips

Always pass large objects (like std::string or std::vector) by `const reference` (const std::string&) to prevent massive performance drops from copying data.

Real-World Example

A swap function requiring pass-by-reference.

example

cpp

#include <iostream>
using namespace std;

void swapVals(int& a, int& b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int x = 10, y = 20;
    swapVals(x, y);
    cout << "x: " << x << " y: " << y << endl; // Prints x: 20 y: 10
    return 0;
}

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