Custom Deleters with std::unique_ptr

std::unique_ptr can be customized with a deleter to control how the managed resource is freed. This feature is useful for handling non-standard resource management scenarios.

What is a Custom Deleter?

A custom deleter is a function or function object that defines how a resource should be released when the std::unique_ptr is destroyed. This is particularly useful when dealing with resources that require specific cleanup actions.

Example

Here’s how you can use a custom deleter with std::unique_ptr:

1#include <iostream>
2#include <memory>
3
4// Custom deleter function
5void CustomDeleter(int* p) {
6  std::cout << "Custom delete called\n";
7  delete p;
8}
9
10void CustomDeleterExample() {
11  std::unique_ptr<int, decltype(&CustomDeleter)>
12    p(new int(10), CustomDeleter);
13}

Explanation

• Custom Deleter Function: CustomDeleter is defined to handle the deletion of int pointers. It prints a message and then deletes the pointer.
• Usage with std::unique_ptr: The std::unique_ptr is constructed with the custom deleter and a raw pointer. When the std::unique_ptr goes out of scope, CustomDeleter is called to clean up the resource.

When to Use Custom Deleters

• Non-Standard Cleanup: When the resource requires special cleanup procedures, such as closing a file handle or releasing a database connection.
• Integration with C Libraries: When working with C libraries that use their own memory management functions.

Summary

Custom deleters in std::unique_ptr provide flexibility for managing resources that need special handling upon release. By defining a custom deleter, you can ensure that the resource is properly cleaned up according to your specific requirements.