Using reset() vs Assignment

When managing resources with smart pointers, you might wonder whether to use the reset() method or directly assign a new smart pointer. Each approach has its use cases and implications.

The reset() method releases the current resource and optionally replaces it with a new one. It is useful when you want to explicitly manage the resource lifetime.

1#include <iostream>
2#include <memory>
3
4void ResetExample() {
5  std::unique_ptr<int> p{
6    std::make_unique<int>(10)};
7  std::cout << *p << '\n';
8
9  p.reset(new int(20)); 
10  std::cout << *p << '\n';
11}

Explanation

• Explicit Resource Management: Using reset() helps to clearly indicate when the resource is being released and replaced. This can be useful for debugging and ensuring resource cleanup.
• Single Ownership: reset() is particularly helpful when you want to change the managed object while maintaining the same smart pointer instance.

Direct assignment creates a new smart pointer, effectively transferring ownership and potentially releasing the old resource.

1void AssignmentExample() {
2  std::unique_ptr<int> p1{
3    std::make_unique<int>(10)};
4  std::unique_ptr<int> p2{
5    std::make_unique<int>(20)};
6
7  p1 = std::move(p2); 
8  if (p2) {
9    std::cout << *p2; 
10  }
11  std::cout << *p1 << '\n';
12}

Explanation

• Ownership Transfer: Direct assignment with std::move() transfers ownership from p2 to p1. The original p2 becomes null.
• Simpler Cases: Direct assignment is straightforward and can be more readable in simpler cases where you are replacing the entire pointer.

• Use reset() when you want to explicitly release and replace a resource while keeping the same smart pointer instance.
• Use Direct Assignment when you want to transfer ownership to a new smart pointer or when dealing with multiple smart pointers.

Both approaches are valid and can be chosen based on the specific needs of your code.