Default Arguments

Overview

Default arguments allow you to omit certain arguments when calling a function, falling back to a predefined default value.

Syntax

cpp

// Default arguments must be at the END of the parameter list
void createProfile(string name, int age = 18, string country = "Unknown") {
    // ...
}

int main() {
    createProfile("Alice"); // age=18, country="Unknown"
    createProfile("Bob", 25); // country="Unknown"
}

Common Pitfalls

Putting default arguments on the left side of the parameter list (e.g., `void func(int x = 5, int y)` is illegal).

Interview Tips

Rule: If a parameter has a default argument, all subsequent parameters to its right MUST also have default arguments.
If a function is declared in a header file, place the default arguments in the declaration (prototype), not the definition.

Real-World Example

A flexible logging system.

example

cpp

#include <iostream>
using namespace std;

void log(string message, string level = "INFO") {
    cout << "[" << level << "] " << message << endl;
}

int main() {
    log("System booted"); // Uses "INFO"
    log("Database failed", "ERROR"); // Overrides default
    return 0;
}

Take C++ Quiz