Should You Nullify Pointers After Deletion in C ?

The Debate Over Nullifying Pointers After Deletion

Smart pointers may relieve developers from concerns about pointer management, but understanding the pitfalls of manual pointer deletion remains crucial. This question examines the practice of setting pointers to NULL after deletion and its potential consequences.

The Argument for Nullifying Pointers

Setting pointers to 0 (interpreted as NULL in standard C ) aims to prevent crashes resulting from double deletions. For instance, if a pointer (e.g., foo) is not nullified after deleting the corresponding object, subsequent deletion attempts will lead to undefined behavior. Nullifying pointers avoids this by intercepting the second deletion.

Consider the following scenario:

Foo* foo = 0; // Sets the pointer to 0 (C++ NULL)
delete foo; // No action taken

Compared to:

Foo* foo = new Foo();
delete foo; // Deletes the object
delete foo; // Undefined behavior

The Counterargument against Nullifying Pointers

Opponents of pointer nullification contend that it merely masks double delete bugs instead of addressing them. Instead, they emphasize the importance of avoiding double deletions altogether. However, in complex codebases with intricate ownership semantics and object lifecycles, eliminating such bugs can be challenging.

Practical Considerations

While it is generally recommended to avoid double deletions, the decision of whether or not to nullify pointers after deletion is context-dependent. When dealing with bugs that cannot be easily eliminated, masking them with pointer nullification can be a viable option.

The Smart Pointer Alternative

As mentioned in the opening statement, std::unique_ptr and std::shared_ptr offer automated pointer management capabilities. By embracing these smart pointers, developers can mitigate the risks associated with raw pointer handling, including double deletions and other memory-related issues.

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