default and delete with example in C++ — Rule of Five & Explicit Control
🔷 What are default and delete?
C++11 introduced these to allow explicit control over compiler-generated special member functions:
= default→ Request the compiler to auto-generate the method.= delete→ Forbid the compiler from generating or using the method.
🔶 Rule of Five – Where It Fits
In modern C++, if you define any one of the following, you should usually define all of them (the Rule of Five):
| Special Function | Purpose |
|---|---|
| Destructor | Cleanup on object destruction |
| Copy Constructor | Copy initialization |
| Copy Assignment Operator | Copy via = |
| Move Constructor | Move initialization (C++11+) |
| Move Assignment Operator | Move via = (C++11+) |
You can use = default or = delete for any of them explicitly.
🔸 Example: Rule of Five Using default and delete
class FileHandler {
public:
FileHandler() = default;
// Disable copy
FileHandler(const FileHandler&) = delete;
FileHandler& operator=(const FileHandler&) = delete;
// Allow move
FileHandler(FileHandler&&) = default;
FileHandler& operator=(FileHandler&&) = default;
~FileHandler() = default;
};✅ This says:
- Do not allow copying.
- Allow move semantics.
- Use default constructor and destructor.
🔷 = delete — Also Useful for Preventing Misuse
❌ Prevent Implicit Conversions
void print(int) = delete;
print(3.14); // ❌ Compile-time error❌ Disable default constructor
class Singleton {
public:
Singleton() = delete;
};